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INDRA Note 1185 INDRA

Feb. 1982 Working

                                                         Paper

RFC 809

                    UCL FACSIMILE SYSTEM
                         Tawei Chang
   ABSTRACT:  This note describes the features  of
              the  computerised  facsimile  system
              developed  in  the   Department   of
              Computer  Science at UCL.  First its
              functions  are  considered  and  the
              related    experimental   work   are
              reported. Then the  disciplines  for
              system    design    are   discussed.
              Finally, the implementation  of  the
              system are described, while detailed
              description are given as appendices.
               Department of Computer Science
                 University College, London
    NOTE: Figures 5 and 6 may be obtained by sending a request to
    Ann Westine at USC-Information Sciences Institute, 4676 Admiralty
    Way, Marina del Rey, California, 90291 (or WESTINE@ISIF) including
    your name and postal mailing address.  Please mention that you are
    requesting figures 5 and 6 from RFC 809.
    OR: You can obtain these two figures online from the files
        <NETINFO>RFC809a.FAX   and   <NETINFO>RFC809b.FAX
    from the SRI-NIC online library.  These files are in the format
    described in RFC 769.

UCL FACSIMILE SYSTEM INDRA Note 1185

                          Contents
1. INTRODUCTION...........................................1
2. SYSTEM FUNCTIONS.......................................2
   2.1 Communication......................................4
   2.2 Interworking with Other Equipment..................8
      2.2.1 Facsimile machines............................8
      2.2.2 Output Devices................................9
   2.3 Image Enhancement..................................11
   2.4 Image Editing......................................15
   2.5 Integration with Other Data Types..................16
3. SYSTEM ARCHITECTURE....................................17
   3.1 System Requirements................................17
   3.2 Hierarchical Model.................................19
   3.3 Clean and Simple Interface.........................20
      3.3.1 Principles....................................21
      3.3.2 Synchronisation and Desynchronisation.........21
      3.3.3 Data Transfer.................................22
   3.4 Control and Organisation of the Tasks..............22
      3.4.1 Command Language..............................23
      3.4.2 Task Controller...............................23
   3.5 Interface Routines.................................26
      3.5.1 Sharable Control Structure....................26
      3.5.2 Buffer Management.............................27
4. UCL FACSIMILE SYSTEM...................................28
   4.1 Multi-Task Structure...............................29
   4.2 The Devices........................................29
   4.3 The Networks.......................................30
   4.4 File System........................................31
   4.5 Data Structure.....................................32
   4.6 Data Conversion....................................34
   4.7 Image Manipulation.................................35
   4.8 Data Transmission..................................39
5. CONCLUSION.............................................41
   5.1 Summary............................................41
   5.2 Problems...........................................42
   5.3 Future Study.......................................46

UCL FACSIMILE SYSTEM INDRA Note 1185

   Appendix I:   Devices
   Appendix II:  Task Controller and Task Processes
   Appendix III: Utility and Data Formats
   Reference
   1. INTRODUCTION
     The object of a  facsimile  system  is  to  reproduce
   faithfully  a document or image from one piece of paper
   onto another piece of paper  sited  remotely  from  the
   first  one.  Up  to  now,  the main method of facsimile
   communication has been via the telephone network.  Most
   facsimile  machines permit neither the storage of image
   page nor their modification before  transmission.  With
   such  machines,  it is almost impossible to communicate
   between different makes of facsimile machines. In  this
   respect,   facsimile   machines   fall   behind   other
   electronic communication services.
     Integration of  a  facsimile  service  with  computer
   communication  techniques  can bring great improvements
   in service. Not only is the reliability and  efficiency
   improved   but,  more  important,  the  system  can  be
   integrated with  other  forms  of  data  communication.
   Moreover, the computer enables the facsimile machine to
   fit into a complete message and information  processing
   environment.   The  storage  facilities provided by the
   computer system make it possible to store large amounts
   of  facsimile  data  and  retrieve  them  rapidly. Data
   conversion allows facsimile machines of different types
   to   communicate  with  each  other.  Furthermore,  the
   facsimile image is edited and/or  combined  with  other
   forms  of  data,  such  as text, voice and graphics, to
   construct a multi-media message, which  can  be  widely
   distributed over computer networks.
     In the Department  of  Computer  Science  at  UCL,  a
   computerised  facsimile  system  has  been developed in
   order to fully apply  computer  technology,  especially
   communication,  to  the facsimile field.  Some work has
   been done to improve the facsimile service  in  several
   areas.
    (1) Adaptation of the facsimile machine for  use  with
        computer networks.  This permits more reliable and
        accurate  document  transmission,   as   well   as
        improving the normal point-to-point transfers.
    (2) Storage  of  facsimile  pages.  This  permits  the
        queueing  of pages, so saving operator time. Also,
        standard documents can  be  kept  permanently  and
        transmitted at any time.
    (3) Interworking with other facsimile  machines.  This
        permits  different  makes of facsimile machines to
  1. 1 -

UCL FACSIMILE SYSTEM INDRA Note 1185

        exchange images.
    (4) Compression of the facsimile images.  This  allows
        more   efficient   transmission  to  be  achieved.
        Different compression schemes are investigated.
    (5) Display of images  on  other  devices.   A  colour
        display  is  used  so  that  the  result  of image
        processing can be shown very vividly.
    (6) Improvement of the images. The ability to  'clean'
        the  facsimile  images  not  only  allows for even
        higher  compression  ratio,  but  also  provide  a
        better result at the destination.
    (7) Editing of  facsimile  pages.  This  includes  the
        ability  to  change  pictures,  alter  the size of
        images  and  merge  two  or   more   images,   all
        electronically.
    (8) Integration of the facsimile  service  with  other
        data  types.   For the time being, coded character
        text can be converted into  facsimile  format  and
        mixed  pages  containing  pictures and text can be
        manipulated.
     This  note  first  considers  the  functions  of  the
   facsimile  system,  the related experimental work being
   reported.  Then the discipline for the system design is
   discussed.  Finally,  the  implementation  of  the  UCL
   facsimile system is described. As appendices,  detailed
   description of the system are given, namely
           I.   Devices
           II.  Task controller and task processes
           III. Utility routines and Data format
   2. SYSTEM FUNCTIONS
     The computerised facsimile system we  have  developed
   is composed of an LSI-11 micro-computer running the MOS
   operating system [14] with two AED62 floppy disk drives
   [17], a Grinnell colour display [18], a DACOM facsimile
   machine [16], and a VDU as  the  system  console.  This
   LSI-11  is also attached to several networks, including
   the ARPANET/SATNET [21], [22]  and  the  UCL  Cambridge
   Ring. A schematic of the system is shown in Fig. 1.
  1. 2 -

UCL FACSIMILE SYSTEM INDRA Note 1185

            facsimile machine  bit-map display
                   +------+    +------+
                   !      !    !      !
                   +------+    +------+
         +------+        \      /        VDU
         ! disk !      +----------+    +-----+
         +------+ ---- !  LSI-11  ! -- !     !
         ! disk !      +----------+    +-----+
         +------+           |
                         +------+
                         !  NI  !
                         +------+
                     Network Interface
          Fig. 1  Schematic of UCL facsimile system
     In this system, a  page  is  read  on  the  facsimile
   machine  and  the  image data produced is stored on the
   floppy disk. This data can be processed locally in  the
   micro-computer  and  then  sent  to  a  file store of a
   remote computer across the  computer  network.  At  the
   remote  site,  the  image  data  may  be  processed and
   printed on a facsimile machine.
     On the other hand, we can receive image data which is
   sent  by a remote host on the network. This data can be
   manipulated in the same way, including being printed on
   the local machine.
     Section 2.1  dicusses  the  problems  concerned  with
   transmission  of  facsimile  image data over a network,
   while the following sections deal with those  of  local
   manipulation of image data.
     In order to interwork with other  facsimile  machine,
   we   have   to   convert   the   image  data  from  one
   representation format  to  another.  Interworking  with
   other  output devices requires that the image be scaled
   to fit the dimension of the destination  device.  These
   are described in section 2.2.
     Being able to process the image by computer opens the
   door  to  many  possibilities.  First, as considered in
   section 2.3, an image can  be  enhanced,  so  that  the
   quality of the image may be improved and more efficient
   storage and transmission can be achieved.  Secondly,  a
   facsimile  editing  system  can  be supported whereby a
   picture can  be  changed  and/or  combined  with  other
  1. 3 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   pictures. This is described in section 2.4.
     In our system, coded character text can be  converted
   into  its  bit-map representation format so that it can
   be  handled  as  a  facsimile  image  and  merged  with
   pictures. This provides an environment where multi-type
   information can be dealt with.  This  is  discussed  in
   section 2.5.
   2.1 Communication
     The first goal of our computerised  facsimile  system
   is  to  use a computer network to transmit data between
   facsimile machines which are geographically separated.
     Normally, facsimile machines are used in  association
   with  telephone  equipment,  the  data being sent along
   telephone lines.  Placing the facsimile machines  on  a
   computer  network  presents  a problem as the facsimile
   machine does not have the ability  to  use  a  computer
   network  directly.   To  perform  the  network  tasks a
   computer is required, and so the  first  phase  was  to
   attach the facsimile machine to a computer.
     The facsimile machine is not like a standard piece of
   computer  equipment.  We  required  a  special hardware
   interface to enable communication between the facsimile
   machine  and  a small computer. This interface was made
   to appear exactly like  the  telephone  system  to  the
   facsimile   machine.   Furthermore,  the  computer  was
   programmed  to  act  exactly  as  if  it  were  another
   facsimile  machine on the end of a telephone line. Thus
   the local facsimile machine could transmit data to  the
   computer  quite happily, believing that it was actually
   talking to a remote facsimile machine on the other  end
   of  a  telephone  wire.  Because of the property of the
   DACOM 6450 used in the experiment [16],  the  interface
   could  be  identical to one developed for connecting to
   an X25 network. The binary synchronous mode of the chip
   used  (SMC  COM5025) was appropriate to drive the DACOM
   machine.
     At the other side of the computer network there was a
   similar  computer  with an identical facsimile machine.
   The problem of transmitting  a  facsimile  picture  now
   appeared  simple:  data  was  taken  from the facsimile
   machine into the computer, transmitted over the network
   as  if  it was normal computer data, and then sent from
   the computer to the facsimile  machine  at  the  remote
   end.  The  data  being  sent  over  the network appears
  1. 4 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   exactly as any other computer data;  there  is  nothing
   special  about  it  to  signify  that  it  came  from a
   facsimile machine.  The  schematic  of  such  facsimile
   transfer system is shown in Fig. 2.
   facsimile
   machine
    +---+  interface
    !   !    +--+    +-----+
    !   ! == !  ! == !     ! computer
    +---+    +--+    +-----+
                        |
                         - - - - - -    computer
                       /             \  network
                       \             /             facsimile
                         - - - - - -               machine
                                    |    interface  +---+
                                 +-----+    +--+    !   !
                        computer !     ! == !  ! == !   !
                                 +-----+    +--+    +---+
              Fig. 2  Facsimile transfer system
     The experimental system was used to perform  a  joint
   experiment  between  UCL  and  two groups in the United
   States. Pictures were exchanged via the  ARPANET/SATNET
   [21],  [22]  between UCL in London, ISI in Los Angeles,
   and  COMSAT  in  Washington   D.C.   (Fig.   3).   This
   environment  was chosen because no equivalent group was
   available in the UK.
     One  problem   concerned   with   such   image   data
   transmission  is  the  quantity of data. Even with data
   compression,  a  single  page  of  facsimile  data  can
   produce  as  much  computer  data  as would normally be
   sufficient   for   sending   over   20,000   alphabetic
   characters  -  or  over a dozen typed pages. Thus for a
   given number of pages put into the system,  an  immense
   amount  of  computer  data is produced. This means that
   the transmission will be slower than for sending  text,
   and  that far more storage will be required to hold the
   data.
     Another problem was encountered which became only too
   apparent  when we implemented this system.  The network
   we were using was often unable  to  keep  up  with  the
   speed of the facsimile machine.  When this happened the
  1. 5 -

UCL FACSIMILE SYSTEM INDRA Note 1185

                    US               UK
                         satellite
   COMSAT                   __
   +---+    +--+           /  \
   !   ! -- !  !           /  \
   +---+    +--+          /    \
     |          \        /      \
   +---+         \      /        \           UCL
   !fax!          \+--+/          \+--+    +---+
   +---+  ARPANET  !  !   SATNET   !  ! -- !   !
                  /+--+            +--+    +---+
                 /                           |
   ISI         /                          +---+
   +---+    +--+                           !fax!
   !   ! -- !  !                           +---+
   +---+    +--+
     |
   +---+
   !fax!
   +---+
   Fig. 3. The three participants of the facsimile experiments
   computer tried to slow down the facsimile machine.  The
   facsimile  machine  would  detect  this 'slowness' as a
   communication problem (as a telephone line would  never
   act  in  this  manner),  and would abandon the transfer
   mid-way through the page.
     This is because the the  facsimile  machine  we  were
   using  was never intended for use on a computer; it was
   designed and built for use on telephone lines.  Indeed,
   being  unaware that it was connected to a computer, the
   facsimile machine transmitted data at a constant  rate,
   which exceeded the limit that the network could accept.
   In other words, the computer network we were using  was
   not  designed for the transfer rate that we were trying
   to use over it.
     Both  these  problems  are  surmountable.   Facsimile
   machines are coming on the market that are designed for
   direct communication with a computer. These machines do
   not  mind  the delays on the computer interface and are
   tolerant of the stops and re-starts. On the other hand,
   if  there were a serious use of facsimile machines on a
   computer network, the network could be designed for the
   high  data rate required. Our problem was aggravated by
  1. 6 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   using a network that was never designed  for  the  data
   rates required in our mode of usage.
     Despite the problems we encountered being a result of
   the  experimental  equipment  we  were working with, we
   still had to  improve  the  situation  to  permit  more
   extensive communications to take place. The easiest way
   to do this was to introduce a local storage area in our
   computer   where  the  data  could  be  held  prior  to
   transmission.  The transfer of a page is  now  done  in
   three  stages.   First, the facsimile data is read from
   the facsimile machine and stored on a local disk.  This
   takes  place  at  high  speed  as  this is just a local
   operation.  When this is complete,  the  data  is  sent
   over  the  network  to  a  disk on the remote computer.
   Finally, the data from  that  disk  is  output  to  the
   remote  facsimile  machine.   This  improved  system is
   shown in Fig. 4.
                   computer network
    fax    computer    - - - -     computer   fax
   +---+   +-----+   /         \   +-----+   +---+
   !   ! = !     ! =     ==>     = !     ! = !   !
   +---+   +-----+   \         /   +-----+   +---+
      - - - + |        - - - -        | + - - >
            | | + - - - - - - - - - + | |
            | | |                   | | |
            V | |                   V | |
            +---+                   +---+
            !   !                   !   !
            !   !                   !   !
            +---+                   +---+
            disk                    disk
       Fig. 4.  The improved facsimile transfer system
     The idea  behind  this  method  is  to  decouple  the
   facsimile  machine from the network communications. The
   data is read from the facsimile machine at full  speed,
   without  the  delays  caused  by  the computer network.
   This also has the effect of being  more  acceptable  to
   the human operators: each page is now read in less than
   a minute.  The transmission over the network then takes
   place  at  whatever speed the network can sustain. This
   does not affect the facsimile machines at all; they are
   not involved in the sending or receiving. Only when all
   the data has been received at the remote  disk  is  the
   remote  facsimile  machine told that the data is ready.
  1. 7 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   The facsimile machine is then given the data as fast as
   it will accept it.
     The disadvantage of such a system is that the  person
   sending  the  pages  does  not know how long it will be
   before they are actually printed at the other side.  If
   several  pages  are  input  in  quick succession by the
   operator, they will be stored on disk; it may  then  be
   some time before the last page is actually delivered to
   the destination. This is  not  always  a  disadvantage;
   where  many  operators  are  sending  data  to the same
   destination, it is a definite advantage to be  able  to
   input  the  pages and have the system deliver them when
   the  destination  becomes  free.  Such  a   system   is
   preferable to use of the current telephone system where
   the  operator  has  to  keep  re-dialing   the   remote
   facsimile machine until the call is answered.
   2.2 Interworking with Other Equipment
   2.2.1 Facsimile machines
     As was mentioned earlier, facsimile machines  produce
   a large amount of data per page due to the way in which
   the pages are encoded.  To reduce the data that has  to
   be  transmitted,  various  compression  techniques  are
   employed.  The manufacturers of facsimile machines have
   developed   proprietary  ways  in  which  the  data  is
   compressed and encoded.  Unfortunately this  has  meant
   that  interworking  of different facsimile machines has
   been impossible.  In the system described in  the  last
   section, exchange of pictures was only possible between
   sites that had identical facsimile  machines.  The  new
   set  of CCITT recommendations will reduce the extent to
   which differences in equipment persist.
     Having  the  data  on  a  computer   gives   us   the
   opportunity  to manipulate data in any way we wish.  In
   particular we could convert the data from the form used
   in  one  facsimile machine to that required by another.
   This means that interworking between different types of
   facsimile machines can be achieved.
     The development of this  system  took  place  in  two
   stages:  the  decompression  of the facsimile data from
   the coded form used in our  machine  into  an  internal
   data  form  and  the  recompression  of the data in the
   internal form into the encoded form  required  for  the
   destination  machine.  Two  programs  were developed to
   perform these two operations.
  1. 8 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     At the same time we were developing  compression  and
   decompression  programs  for  machines  that  use other
   techniques.  In particular, we  developed  programs  to
   handle  the  recently approved CCITT recommendation for
   facsimile compression [15]. The CCITT came up with  two
   varieties of compression, depending upon the resolution
   being used.
     Unfortunately there were no facsimile machines on the
   network  that  use  the  CCITT  compression  technique.
   However, the programming of the  new  methods  achieved
   two  goals:  it proved that the data could be converted
   inside a small computer, so that machines of  different
   types could be supported on the network, and it enabled
   us  to  compare  the  compression  results.  These  are
   described  in  more detail in [13].  Essentially, these
   show that the DACOM technique  used  by  our  facsimile
   machine  is  comparatively  poor, and that considerably
   less data need be transmitted if some other  method  is
   used.  This  brings  up  another  possibility: we could
   change the compression of the data to reduce the volume
   for transmission and then change the data back again at
   the   destination.   This   may    save    considerable
   transmission  time,  especially  if  fast  computers or
   special hardware was easily available.   This  has  not
   been  tried  yet  in  our  system, as none of the other
   users on the network have the  capability  of  changing
   the  data  format  back  into  that  required  by their
   machines.
     There  are  many  other  more  efficient  compression
   schemes,  e.g.   block  compression  [7] and predictive
   compression [8], but we have not yet incorporated  them
   into our system.
   2.2.2 Output Devices
     One area that we have explored is the use of  devices
   other  than facsimile machines for outputting the data.
   Facsimile  machines  are  both  expensive  to  buy  and
   relatively  slow  to  operate. We have investigated the
   use of a TV-like screen to display the  data,  just  as
   character VDUs are commonly used to display text.  This
   activity requires bit-map displays, with an address  in
   memory  for each postion on the screen. Full colour and
   multiple shades can be used  with  appropriately  large
   bit-map  storage.   Although  simple  in principle, the
   implementation  of   the   relevant   techniques   took
   considerable effort.
  1. 9 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     The problems arise in  the  way  that  the  facsimile
   image  is encoded. Raw facsimile images consist of rows
   of small dots, each dot recorded as a  black  or  white
   space. When these dots are arranged together they build
   up a picture in a similar manner to the way in which  a
   newspaper  picture is made up. Unfortunately the number
   of dots used in a facsimile page is not the same as the
   number  used  on  most screens. For instance, the DACOM
   facsimile machine uses 1726 dots across each page,  but
   across  a  screen there are usually just 512 dots. Thus
   to show the picture on the screen the 1726 dots must be
   'squeezed' into just 512 dots; stated another way, 1214
   dots must be thrown away without losing the picture!
     It is in reducing the number of picture elements that
   the  problem  arises.  We could just every third dot or
   so from the facsimile  page  and  just  display  those.
   Alternatively,  we  could  take three or more at a time
   and try to convert the group  of  them  into  a  single
   black  or  white  dot.   Unfortunately,  in  both these
   cases, data can get  lost  that  is  necessary  to  the
   picture.   For  instance,  a  facsimile  encoding of an
   architect drawing could easily end up with  a  complete
   line  removed,  radically  changing the presentation of
   the image.
     After much experimentation, we developed a method  of
   reducing  the  number  of  dots  without destroying the
   picture. This is  a  thinning  technique,  whereby  key
   elements  of  the picture are thinned, but not removed.
   Occasionally, when  the  detail  gets  too  fine,  some
   elements  are merged, but under these circumstances the
   eye would not have been able to see the detail  anyway.
   The  details of this technique are described in [3] and
   [4].
     It may also be required that a picture  be  enlarged.
   This enlargement can be done by simply duplicating each
   pixel in the picture.  For a  non-integral  ratio,  the
   picture  can  be expanded up to the nearest integer and
   then shrunk to the correct size.  However, this  method
   may degrade the image quality, e.g. the oblique contour
   may become stepped,  especially  when  the  picture  is
   enlarged  too much. This problem can be solved by using
   an iterative enlargement algorithm. Each time  a  pixel
   is  replaced  with a 2x2 array of pixels, whose pattern
   depends  on  the  original   pixel   and   the   pixels
   surrounding  it.  This  procedure is repeated until the
   requested ratio is reached. If  the  ration  is  not  a
   power  of 2's, the same method as that for non-integral
   ratios is used.
  1. 10 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     As a side effect of  developing  this  technique,  we
   could  freely  change  the  size and shape of an image.
   The picture can be expanded or shrunk,  or  it  can  be
   distorted.   Distortion,  whereby  the  horizontal  and
   vertical dimensions of the  image  may  be  changed  by
   different amounts, is often useful in image editing.
     The immediate consequence of this ability  to  change
   the image size meant that we could display the image on
   a screen as well as output the  image  on  a  facsimile
   machine.  To  a user of a computerised facsimile system
   this could be a very  useful  feature:  images  can  be
   displayed  on  screen  much  faster than on a facsimile
   machine, and displays are  significantly  cheaper  than
   the  facsimile machines as well. It is possible that an
   installation could have many screen displays where  the
   image  could  be viewed, but perhaps only one facsimile
   machine would be available for hard copy. This would be
   similar to many computer configurations today where the
   number of printers is limited due to  their  cost,  and
   display screens are far more numerous.
   2.3 Image Enhancement
     One aspect of computer processing that we  wanted  to
   investigate  was  that  of image enhancement. Enhancing
   the image is a  very  tricky  operation;  as  the  name
   implies  it  means  that  the image is improved in some
   sense.  Under program  control  this  is  difficult  to
   achieve: what the program thinks is an improvement, the
   human might judge to be distinctly worse.
     Our enhancement attempts were aimed  particularly  at
   printed  documents  and  other forms of typed text. The
   experiment was double pronged: we  hoped  to  make  the
   image  easier  to  read by humans while also making the
   image easier for the computer to handle.
     In our earlier experiments we had  noticed  that  the
   encoding  of  printed  matter was often very poor. This
   was especially noticeable when we  enlarged  an  image.
   Rather  than  each  character having smooth edges as on
   the original  document,  the  edges  were  very  rough,
   unexpected notches and excrescences being caused by the
   facsimile scanner.  They not  only  degrade  the  image
   quality but also decrease the compression efficiency. A
   typical enlargement of several characters is  shown  in
   Fig. 5.
  1. 11 -

UCL FACSIMILE SYSTEM INDRA Note 1185

           Fig 5.  An enlargement of an typed text
     The enhancement method we adopted was first  employed
   at  Loughborough  University  [5].  This method has the
   effect of smoothing the edges of the dark areas on  the
   image.  The  technique consists of considering each dot
   in the image in turn. The dot is either left as  it  is
  1. 12 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   or changed to the opposite colour (white  to  black  or
   black  to  white)  depending  upon  the eight dots that
   surround it. The particular pattern of surrounding dots
   that  are  required to change the inner dot's colour is
   used to control the harshness  of  the  algorithm  [6],
   [8].
     In our  first  set  of  experiments  the  result  was
   definitely  worse  than  the original. Although square-
   like characters such as H, L, and T came out very well,
   anything  with slope (M, V, W, or S) became so bad that
   the oblique  contours  were  stepped.  The  method  was
   subsequently  modified to produce a result that was far
   more acceptable; the image looked a  lot  cleaner  than
   the  original.  Fig.  6  shows the same text as that in
   Fig. 5, but after it has been cleaned.
  1. 13 -

UCL FACSIMILE SYSTEM INDRA Note 1185

                   Fig. 6  A cleaned text
     The effect of these can be difficult to see  clearly.
   We have used the colour on our Grinnell display to show
   the original picture and the outcome of various picture
   processing  operations superposed in different colours.
   This brings out  the  effect  of  the  operations  very
  1. 14 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   vividly.
     It was mentioned above that the enhancement was  done
   not  only to improve the image for reading but also for
   easier  processing  by  the  computer.   As   described
   earlier,  the  image  from  the  facsimile  machine  is
   compressed in order to reduce the amount of data.   The
   cleaning  allows a higher compression rate so that more
   efficient transmission and/or storage can be achieved.
     We  learned   some   important   lessons   from   the
   enhancement  exercise.   Originally we thought that the
   main attraction in enhancement would be to improve  the
   readability.  In  the  end, we found that improving the
   readability was very difficult, especially because  the
   facsimile  image was so poor. Instead we found that the
   effect of  reducing  the  compressed  output  was  more
   important.  By reducing the data to be transmitted by a
   quarter, significant savings could be made. But  before
   such  a  technique  could be used in a live system, the
   time it  takes  to  produce  the  enhancement  must  be
   weighed  against  the  time  that  would  be  saved  in
   transmission.
   2.4 Image Editing
     By editing we mean that the facsimile picture can  be
   changed,  or  combined with other pictures, while it is
   stored inside the computer.  In  previous  sections  it
   was  mentioned  that we could change the size and shape
   of a facsimile image. This technique was later combined
   with  an  overlaying method that enabled one picture to
   be combined with another [12].
     In order to perform any editing it  is  necessary  to
   have  the picture displayed for the user to see. In our
   case we displayed the picture on  the  bit-map  screen.
   The image took up the left-hand side of the screen, the
   right side being reserved  for  the  picture  that  was
   being  built.   The  user  could  select an area of the
   left-hand screen and move  it  to  a  position  on  the
   right-hand  screen.   Several images could be displayed
   in succession on the left, and areas selected and moved
   to  the right.  Finally, the right-hand screen could be
   printed on the facsimile machine.
     The selection of an area of the picture was  done  by
   the   use   of   a   coloured  rectangular  subsection,
   controlled by a program in the computer, that could  be
   moved  around on the screen. The rectangular subsection
  1. 15 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   was moved with instructions typed in by  the  operator;
   it  could  be  moved  up  or  down,  and  increased  or
   decreased in size. When the  appropriate  area  of  the
   screen  had  been  selected, the program remembered the
   coordinates  and   moved   the   coloured   rectangular
   subsection  to  the  right-hand side of the screen. The
   user then selected an area again, in a similar  manner.
   When the user finished the editing, the program removed
   the part of the picture  selected  from  the  left-hand
   screen  and  converted  it  to  fit  the  shape  of the
   rectangular subsection on the  right-hand  screen.  The
   result was then displayed for the user to see.
     When an image was being edited,  the  editor  had  to
   keep  another  scaled  copy for display. This is due to
   the fact that the screen had a different  dimension  to
   that  of the facsimile machine. The editing operations,
   e.g.  chopping  and  merging,  were  performed  on  the
   original  image  data  files  with  the full resolution
   available on the facsimile machine.
   2.5 Integration with Other Data Types
     The facsimile  machine  can  be  viewed  in  a  wider
   context than merely a facsimile input/output device. It
   can work as a printer  for  other  data  representation
   types,  such  as  coded  character  text  and geometric
   graphics.  At  present,  text  can  be  converted  into
   facsimile  format and printed on the facsimile machine.
   Moreover, mixed pages containing pictures and text  can
   be  manipulated  by  our  system.  The  integration  of
   facsimile images with geometric graphics is a topic  of
   future research.
     In order to  convert  a  character  string  into  its
   facsimile  format,  the  system maintains a translation
   table whereby the patterns of the characters  available
   in  the  system  can  be retrieved. The input character
   string is translated into a set of scan lines, each  of
   which  is  created  by  concatenating the corresponding
   patterns of the characters in the string.
     The translation table is in  fact  a  software  font,
   which  can be edited and modified. Even though only one
   font is available in our system for the time being,  it
   is  quite  easy  to  introduce  other  character fonts.
   Furthermore, it is also  possible  for  a  font  to  be
   remotely  loaded  from a database via the communication
   network.
  1. 16 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     This allows for more interesting applications of  the
   facsimile  machine.  For  example,  it could serve as a
   Teletex printer, provided that  the  Teletex  character
   font  is included in our system. In this case, the text
   images may be distorted to fit the presentation  format
   requested  by  the Teletex service.  Similarly, Prestel
   viewdata pages  could  be  displayed  on  the  Grinnell
   screen.
     Moreover,  pictures  can  be  mixed  with   text   by
   combining   this   text  conversion  with  the  editing
   described in  the  previous  section.  This  should  be
   regarded   as   a   notable   step  towards  multi-type
   processing.
     Not  only  does  this  support  a  local   multi-type
   environment   but   multi-type   information   can   be
   transmitted over a network. So far  as  this  facsimile
   system  is  concerned, a mixed page containing text and
   pictures can be sent only when it has been  represented
   in  a  bit-map  format.  However,  much  more efficient
   transmission would be achieved if  one  could  transmit
   the text and pictures separately and reproduce the page
   at the destination site. This requires  that  a  multi-
   type  data structure be designed which is understood by
   the two communication sites.
   3. SYSTEM ARCHITECTURE
     Now let us discuss the general disciplines for design
   and  implementation  of a computerised facsimile system
   which  carries  out  the  functions  described  in  the
   previous  sections.   Having discussed the requirements
   of the system, a hierarchical model  is  introduced  in
   which  the  modules of different layers are implemented
   as separate processes.  The Clean and Simple interface,
   which  is  adopted  for inter-process communication, is
   then  described.   The  task   controller,   which   is
   responsible  for  organising  the  tasks  involved in a
   requested job, is discussed in  detail.   Some  efforts
   have  been  made  in our experimental work to provide a
   more convenient user programming environment and a more
   efficient   data   transfer  method.  This  is  finally
   described.
   3.1 System Requirements
     In a computerised facsimile system,  the  images  are
   represented  in  a  digital  form.  To  carry  out this
  1. 17 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   conversion, a page is scanned by the optical scanner of
   the  facsimile machine, a digital number being produced
   to represent  the  darkness  of  each  pixel.  As  high
   resolution  has to be adopted to keep the detail of the
   image, the facsimile  data  files  are  usually  rather
   large.  In  order  to  achieve  efficient  storage  and
   transmission, the facsimile data must be compressed  as
   much as possible.
     Currently, the facsimile machines made  by  different
   manufacturers   h different  properties,  such  as
   different compression methods and different resolution.
   There   are   also  some  international  standards  for
   facsimile data compression, which are employed for  the
   facsimile  data  to be transferred over the public data
   network. These  require  that  the  facsimile  data  be
   converted  from  one representation form to another, so
   that users who are  separated  geographically  and  use
   different  machines  can  communicate  with each other.
   More sophisticated applications,  e.g.  image  editing,
   request processing facilities of the system as well.
     When being processed, the facsimile image  should  be
   represented   in  a  common  format  or  internal  data
   structure,  which  is  used  to  pass  the  information
   between  different processing routines. For the sake of
   convenience and efficiency, the internal data structure
   should  be fairly well compressed and its format should
   be  easy  for  the  computer  to  manipulate.  In   our
   experimental  work,  the  line  vector  is  chosen as a
   standard unit, a simple  run-length  compression  being
   employed  [3].  Some  processing routines may use other
   data   formats,   e.g.   bit-map,   but   it   is   the
   responsibility   of   such   routines  to  perform  the
   conversion between those formats and the standard one.
     The  system   should   contain   several   processing
   routines,  each  of  which performs one primitive task,
   such  as  chopping,  merging,  and  scale-changing.  An
   immense variety of processing operations can be carried
   out as long as those  task  modules  can  be  organised
   flexibly. The capability for flexible task organisation
   should be thought of  as  one  of  the  most  important
   requirements of the system.
     One  possibility  is  for  the  processing   routines
   involved  to  be  executed  separately, temporary files
   being used as communication media. Though very  simple,
   this method is far too inefficient.
  1. 18 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     As described above,  the  information  unit  for  the
   communication  between  the  processing routines is the
   line vector, so that the routines can be  organised  as
   embedded  loops,  where  a processing routine takes the
   input line from its source routine located in the inner
   loop,  and  passes  the  output line to the destination
   routine located in the outer loop [3].  Obviously  this
   method  is quite efficient. But it is not realistic for
   our system, because it is very difficult  to  build  up
   different  processing  loops  at  run-time and flexible
   task organisation is impossible.
     In a  real-time  operating  system  environment,  the
   primitive   tasks   can   be  implemented  as  separate
   processes. This method, which is discussed in detail in
   the   following   sections,   provides   the   required
   flexibility.
   3.2 Hierarchical Model
     As shown in Fig. 7, the modules in a single  computer
   fall into three layers.
                     +---------+
                     !         ! task controller
                     +---------+
                            tasks
              +---+  +---+  +---+  +---+  +---+
              !   !  ! !   !  !   !  !   !
              +---+  +---+  +---+  +---+  +---+
                |      |                    |
              +---+  +---+                +---+
              !   !  !   ! device drivers !   !
              +---+  +---+                +---+
          - - - | - -  |  - - - - - - - - - | - - - -
              +---+  +---+                +---+
              !   !  !   !    physical    |   !
              !   !  !   !    devices     !   !
              +---+  +---+                +---+
               Fig. 7  The hierarchical model
     These are:
    (1) Device Drivers, which constitute the lowest  layer
        in the model.  The modules in this layer deal with
        I/O activities of the physical  devices,  such  as
  1. 19 -

UCL FACSIMILE SYSTEM INDRA Note 1185

        facsimile machine, display and floppy  disk.  This
        layer  frees  the task modules of upper layer from
        the burden of I/O programming.
    (2) Tasks, which perform all processing primitives and
        handle different data structures. Above the driver
        of each physical device, there  are  one  or  more
        such  device-independent  modules,  which  work as
        information source or sink in the task chain  (see
        below).  A file system module allows other modules
        to store and retrieve information on the secondary
        storage  device such as floppy disk. Decompression
        and recompression routines convert data structures
        of   facsimile   image  information  so  that  the
        facsimile machines can communicate with  the  rest
        of   the   system.   Processing  primitives,  e.g.
        chopping, merging,  scaling,  are  implemented  as
        task modules in this layer. They are designed such
        that they can be concatenated to  carry  out  more
        complex  jobs.  So far as the system is concerned,
        the protocols for data transmission over  computer
        networks are also regarded as task modules in this
        layer.
    (3)  Task  Controller,  which   organises   the   task
        processes   to   perform  the  specified  job.  It
        provides the users of the application layer with a
        procedure-oriented  language whereby the requested
        job can be defined as a  chain  of  task  modules.
        Literally, the chain is represented by a character
        string:
           <source_task>|{<processing_task>|}<sink_task>
          According to such a command, the task controller
        selects the relevant task modules and concatenates
        them in proper order by means  of  logical  links.
        Then the tasks on the chain are executed under its
        control, so that the data taken  from  the  source
        are processed and the result is put into the sink.
   3.3 Clean and Simple Interface
     It is important, in this application, to develop  the
   software  in  a  modular  way.  It  is desirable to put
   together a set of modules to carry  out  the  different
   image   processing  tasks.  Another  set  of  transport
   modules must be developed for shipping  data  over  the
  1. 20 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   different networks to which the UCL system is attached.
   In   our  computerised  facsimile  system,  these  task
   modules are  implemented  as  separate  processes.  The
   operation  of  the  system  relies on the communication
   between these processes.  The interface which  is  used
   for   such   communication  has  been  designed  to  be
   universal; it is independent of these modules, and  has
   been  termed  the Clean and Simple interface [20]. This
   interface is discussed in this section.
   3.3.1 Principles
     The Clean and Simple interface is concerned with  the
   synchronisation   and   transfer  of  full-duplex  data
   streams between two communicating processes.  Thus  the
   interface   has   three  major  components:  connection
   synchronisation,   data   transfer    and    connection
   desynchronisation.   These   components  are  discussed
   below.
     The connection between two processes is initiated  by
   one  of  them,  which, generally speaking, belongs to a
   higher  layer.  For  example,  the  interface   between
   protocols  of  different  layers is always initiated by
   the higher layer, though, sometimes, the connection  is
   initiated  passively by the primitive 'listen'. It will
   be seen in the next section  that  task  processes  can
   communicate  with each other via the connections to the
   higher  layer  (task  controller)  and  this  makes  it
   possible to achieve flexible task organisation.
     The process initiating the connection is  called  the
   'master' process, while the other is called the 'slave'
   process. The 'master' process is also  responsible  for
   resource   allocation   for   the   two   communicating
   processes. Here 'resource' refers mainly to the  memory
   areas  for  the message structure and data buffer. This
   asymmetric definition of the interface  eliminates  any
   possible confusion in resource allocation.
     The interface is implemented by using the signal-wait
   mechanism  provided  by  the  operating  system. A data
   structure called CSB (Clean and  Simple  Block),  which
   contains  function, data buffer, and other information,
   is sent as the event message, when one process  signals
   another [20].
  1. 21 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   3.3.2 Synchronisation and Desynchronisation
     The  procedure  for  connection  synchronisation   is
   composed   of  two  steps.  First,  the  two  processes
   exchange their identifiers for the specific  connection
   by  means  of a getcid primitive.  Usually, the pointer
   to the task control structure of the process is used as
   the connection identifier.
     Then, the 'master' sends an open CSB with appropriate
   parameter    string    passing    the    initialisation
   information. This information, which can also be called
   open   parameter,   is   process   dependent,  or  more
   accurately, task dependent. For example, the parameters
   for  the  file  system  should be the file name and the
   access mode. Provided the 'slave' accepts the  request,
   the connection is established successfully and data can
   be transferred via the interface.
     In  order  to  desynchronise  the   connection,   the
   'master' initiates a 'close' action. On the other hand,
   an error state or  EOF  (end  of  file)  state  can  be
   reported   by  the  'slave'  to  request  a  connection
   desynchronisation.
     The listen primitive in our system  is  reserved  for
   the  processes  that  receive a request from the remote
   hosts on the networks.
   3.3.3 Data Transfer
     While the Clean and Simple interface is asymmetric in
   relation  to  connection synchronisation, data transfer
   is completely symmetric so long as the  connection  has
   been  established.  Data  flows  in both directions are
   permitted, though the operations are quite different.
     The  interface  provides  two  primitives  for   data
   transfer  --  read  and write. To transfer some data to
   the  'slave',  the  'master'  signals  it  with  a  CSB
   containing  the write function and a buffer filled with
   the data to be transferred.  Having consumed the  data,
   the 'slave' returns the CSB to report the result status
   of the transmission.
     On the other hand, in order to receive some data from
   the 'slave', the 'master' uses a read CSB with an empty
   buffer. Having received the CSB, the 'slave' fills  the
   buffer  with  the data requested and, then, returns the
   CSB.
  1. 22 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   3.4 Control and Organisation of the Tasks
     Another  important  aspect   of   the   multi-process
   architecture  of  the UCL facsimile system, is the need
   to systematise the  control  and  organisation  of  the
   tasks.  This  activity  is  the  function  of  the task
   controller, whose  operations  are  discussed  in  this
   section.
   3.4.1 Command Language
     As mentioned earlier, the task controller supports  a
   procedure-oriented  language by means of which the user
   or the routines of the upper layers can define the jobs
   requested.  A  command  should  contain  the  following
   information:
     1. the names of the task processes which are involved
        in the job.
     2. the open parameters for these task processes.
     3. the order in which the tasks are to be linked.
     The last item is quite  important,  though,  usually,
   the same order as that given in the command is used.
     A command in this language is presented  as  a  zero-
   ended  character  string.  In the task name strings and
   the attribute strings of the open parameters, '|', '"',
   and  ','  must  be  excluded as they will be treated as
   separators. The definition is shown below,  where  '|',
   which  is  the  separator of the command strings in the
   language, does not mean 'OR'.
   <command_string> ::= <task_string>
   <command_string> ::= <task_string>|<command_string>
   <task_string> ::= <task_name>
   <task_string> ::= <task_name>"<open_parameter>
   <open_parameter> ::= <attribute>
   <open_parameter> ::= <attribute>,<open_parameter>
   3.4.2 Task Controller
     In our experimental work, the task controller  module
   is  called  fitter.   This  name which is borrowed from
   UNIX hints how the  module  works.   According  to  the
   command  string,  it  links  the specified tasks into a
   chain, along which the data is processed to fulfil  the
  1. 23 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   job requested (Fig. 8).
                          tasks
              +-----+    +-----+    +-----+
              !  a  ! -> !  b  ! -> !  c  !
              +-----+    +-----+    +-----+
                   Fig. 8  The task chain
     Since  all  modules,  including  fitter  itself,  are
   implemented   as  processes,  the  connections  between
   modules should be via the Clean and Simple  interfaces.
   Upon  receiving  the  command string, the fitter parses
   the string to find each task process involved and opens
   a  connection  to  it. Formally, the task processes are
   chained directly, but, logically, there  is  no  direct
   connection  between  them. All of them are connected to
   the fitter (Fig. 9).
                         fitter
                     +-------------+
                 +-- !             ! --+
                 |   +-------------+   |
                 |          |          |
                 V          V          V
              +-----+    +-----+    +-----+
              !  a  !    !  b  !    !  c  !
              +-----+    +-----+    +-----+
        Fig. 9 The connection initiated by the fitter
     For each of the processes  it  connects,  the  fitter
   keeps  a  table called pipe. When the command string is
   parsed, the pipe tables are double-linked to  represent
   the specified order of data flow. So far as one process
   is concerned, its pipe table contains two  pointers:  a
   forward  one pointing to its destination and a backward
   one pointing to its sources. Besides the  pointers,  it
   also  maintains  the  information  to identify the task
   process and the corresponding connection.
  1. 24 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     Fig. 10 illustrates the chain of the pipe tables  for
   the  job "a|b|c".  Note that the forward (output) chain
   ends at the sink, while the backward (input) chain ends
   at  the  source.  In this sense, the task processes are
   chained in the specified order  via  the  fitter  (Fig.
   11). The data transfer along the chain is initiated and
   controlled by the  fitter,  each  process  getting  the
   input  from  its  source  and putting the output to its
   destination.
             +-----+    +-----+    +-----+
             !  * -+--> !  * -+--> !  0  !
             +-----+    +-----+    +-----+
             !  0  ! <--+- *  ! <--+- *  !
             +-----+    +-----+    +-----+
             !  a  !    !  b  !    !  c  !
             +-----+    +-----+    +-----+
             !     !    !     !    !     !
             !     !    !     !    !     !
             +-----+    +-----+    +-----+
                   Fig. 10  The pipe chain
                         fitter
                     +-------------+
                 +-> ! * -> * -> * ! --+
                 |   +-------------+   |
                 |         | A         |
                 |         V |         V
              +-----+    +-----+    +-----+
              !  a  !    !  b  !    !  c  !
              +-----+    +-----+    +-----+
                   Fig. 11  The data flow
     This strategy makes the task organisation so flexible
   that  only the links have to be changed when a new task
   chain is to be built up. In such an  environment,  each
   task process can be implemented independently, provided
   the Clean and Simple interface is supported. This  also
   makes the system extension quite easy.
  1. 25 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     The fitter manipulates one job at a time. But it must
   maintain  a  command  queue  to cope with the requests,
   which come simultaneously from either the  upper  level
   processes or other hosts on the network.
   3.5 Interface Routines
     In a modular, multi-process system such  as  the  UCL
   facsimile   system,  the  structure  of  the  interface
   routines is very important. The CSI of section  3.3  is
   fundamental  to the modular interface; a common control
   structure is also essential. This  section  gives  some
   details  both  about the sharable control structure and
   the buffer management.
   3.5.1 Sharable Control Structure
     Though the CSI specification is straightforward,  the
   implementation   of   the  inter-process  communication
   interface may be  rather  tedious,  especially  in  our
   system,  where  there  are  many  task  processes to be
   written. Not only does each process have  to  implement
   the  same  control  structure  for signal handling, but
   also the buffer management routines must be included in
   all the processes.
     For the sake of simplicity and efficiency, a  package
   of  standard  interface  routines is provided which are
   shared by the  task  processes  in  the  system.  These
   routines  are re-entrant, so that they can be shared by
   all processes.
     The 'csinit' primitive is called for a  task  process
   to check in.  An information table is allocated and the
   pointer to the table is returned to the caller  as  the
   task  identifier,  which is to be used for each call of
   these interface routines.
     Then,  each  task  process  waits  by  invoking   the
   'csopen'  primitive  which  does  not  return until the
   calling process  is  scheduled.   When  the  connection
   between  the process and the fitter is established, the
   call returns the pointer to the open  parameter  string
   of  the  task,  the corresponding task being started. A
   typical structure of the task process (written in c) is
   shown  below.  After  the task program is executed, the
   process calls the 'csopen' and waits again. It  can  be
   seen  that  the  portability  of  the  task routines is
   improved to a great extent. Only the interface routines
  1. 26 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   should be changed if  the  system  were  to  run  in  a
   different operating environment.
   static int mytid;       /* task identifier */
   task()
   {
           char *op;       /* open parameter */
           mytid = csinit();
           for(;;) {
                   op = csopen(mytid);
                   ...     /* the body of the task */
           }
   }
   3.5.2 Buffer Management
     The package of the interface routines also provides a
   universal buffer management, so that the task processes
   are freed from this burden. The allocation of the  data
   buffers  is  the  responsibility  of  the  higher level
   process, the fitter. If the  task  processes  allocated
   their own buffers, some redundant copying would have to
   be  done.  Thus,  the  primitives  for  data  transfer,
   'csread' and 'cswrite', are designed as:
           char *csread(tid, need);
           char *cswrite(tid, need);
   where 'tid' is the identifier of the task and 'need' is
   the  number  of  data  bytes  to  be  transferred.  The
   primitives return the pointer to  the  area  satisfying
   the  caller's requirement. The 'csread' returns an area
   containing  the  data  required  by  the  caller.   The
   'cswrite'  returns  an  area  into which the caller can
   copy the data to be transferred. The copied  data  will
   be  written to its destination at a proper time without
   the caller's interference.  Obviously  the  unnecessary
   copy  operations can be avoided. It is recommended that
   the data buffer returned  by  the  primitives  be  used
   directly to attain higher performance.
  1. 27 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     In order to implement  this  strategy,  each  time  a
   piece  of  data  is  required,  the  size of the buffer
   needed is compared with that of the unused buffer  area
   in  the current CSB. If the latter is not less than the
   former,  the  current  buffer  pointer   is   returned.
   Otherwise,  a  temporary buffer has to be employed. The
   data is copied into the buffer until the requested size
   is  reached.  In  this  case,  instead of a part of the
   current buffer, the temporary buffer will be returned.
     A 'cswrite' call with the 'need' field  set  to  zero
   tells  the  interface routine that no more data will be
   sent. It causes  a  'close'  CSB  to  be  sent  to  the
   destination routine.
     If there  is  not  enough  data  available,  'csread'
   returns zero to indicate the end of data.
   4. UCL FACSIMILE SYSTEM
     Now we discuss the implementation of the computerised
   facsimile   system   developed  in  the  Department  of
   Computer Science at UCL.
     This system has several components. Since  the  total
   system  is  a modular and multi-process one, a specific
   system must be built up for a specific application. The
   way  that this is done is discussed in section 4.1. The
   specific devices and their  drivers  are  described  in
   section  4.2. The system can be attached to a number of
   networks.  In  the  UCL  configuration,   the   network
   interface  can be direct to SATNET [22], SERC NET [23],
   PSS [24], and the Cambridge Ring. The form  of  network
   connection  is  discussed  further  in section 4.3. The
   system must transfer data between the facsimile devices
   and  the disks, and between the networks and the disks.
   For this a filing system is required which is discussed
   in section 4.4.
     A key aspect of the  UCL  system  is  flexibility  of
   devices, networks, and data formats. The flexibility of
   device is achieved by the modular nature of the  device
   drivers  (section  4.2).  The flexibility of network is
   discussed in section 4.8. The additional flexibility of
   data   structure  is  described  in  section  4.5.  The
   flexibility can be utilised by incorporating conversion
   routines  as in section 4.6. An important aspect of the
   UCL system is the ability to provide local manipulation
   facilities  for  the  graphics  files.   The facilities
   implemented for the local manipulation are discussed in
  1. 28 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   section 4.7.  In  order  to  transfer  files  over  the
   different  networks  of  section 4.3. a high level data
   transmission protocol must be defined.  The  procedures
   used in the UCL system are discussed in section 4.8.
   4.1 Multi-Task Structure
     The  task  controller  and   processing   tasks   are
   implemented  as  MOS  processes.  A  number  of utility
   routines are provided  for  users  to  build  new  task
   processes and modules at application level.
     In the environment of MOS, a process is included in a
   system  by  specifying a Process Control Table when the
   system is built up. The macro  'setpcte'  is  used  for
   this  purpose,  the  meaning  of  its  parameters being
   defined in [14].
   #define setpcte(name,entry,pridev,prodev,stklen,
       relpid,relopc)
     {0,name,entry,pridev,prodev,stklen,relpid,relopc}
     A Device Control Table (DCT) has to be specified  for
   each  device  when the system is built up. A DCT can be
   defined anywhere as devices are referenced by  the  DCT
   address.  The  macro  'setdcte'  is designed to declare
   devices, the meanings of its parameters being specified
   in   [14].    This   method   is  used  in  the  device
   descriptions.
   #define setdcte(name,intvec,devcsr,devbuf,devinit,
       ioinit,intrpt,mate)
     {04037,intrpt,0,0,name,mate,intvec,devinit,
       devcsr,devbuf,ioinit}
   4.2 The Devices
     As mentioned in section 2,  apart  from  the  general
   purpose  system console, there are three devices in the
   system to support the facsimile service. These are:
    (1) AED62 Floppy Disk, which is used as the  secondary
        memory storing the facsimile image data. Above its
        driver, a file system is implemented to manage the
        data  stored  on  the disks, so that an image data
  1. 29 -

UCL FACSIMILE SYSTEM INDRA Note 1185

        file can be accessed through the Clean and  Simple
        interface.  This file system is dicussed in detail
        in the next section. For some processing jobs, the
        image  data  has  to  buffered on a temporary file
        lest time-out occurs on the facsimile machine.
    (2) DACOM Facsimile Machine, which is  used  to  input
        and  output  image  data.  It  reads  an image and
        creates the corresponding data  stream.  On  other
        hand, it accepts the image data and reproduces the
        corresponding image. Above its driver, there is  a
        interface  task  to fit the facsimile machine into
        the system, the Clean and Simple  interface  being
        supported.   The  encoding algorithm for the DACOM
        machine is described in [19].
    (3) Grinnell Colour Display,  which  is  used  as  the
        monitor  of  the  system.  Above  its  driver,  an
        interface task is implemented so  that  the  image
        data  in  standard  format can be accepted through
        the Clean and Simple interface.
     The detailed description  of  these  devices  can  be
   found  in  Appendix  1.  The  interface  task  and  the
   description for each device are listed in the following
   table. The interface tasks can be directly used as data
   source or sink in a task string.
         Device       Interface Task  Description
   AED62 Floppy Disk        fs()      aed62(device)
   DACOM fax Machine       fax()      dacom(device)
   Grinnell Display   grinnell()      grinnell(device)
     Note that the DCTs  for  the  facsimile  machine  and
   Grinnell    display   have   been   included   in   the
   corresponding interface tasks, so that there is no need
   to declare them if these tasks are used.
   4.3 The Networks
     There   are   three   relevant   wide-area   networks
   terminating  in  the  Department of Computer Science at
   the end of 1981. These are:
    (1) A British Telecom X25 network (PSS, [24]).
    (2) A private X25 network (SERC NET, [23])
  1. 30 -

UCL FACSIMILE SYSTEM INDRA Note 1185

    (3) A Defence network (ARPANET/SATNET, [21], [22])
     In addition there is a  Cambridge  Ring  as  a  local
   network.
     For the time  being,  the  UCL  facsimile  system  is
   directly  attached to the various networks at the point
   NI (Network Interface) of Fig. 1.
     As mentioned earlier, pictures can be  exchanged  via
   the  SATNET/ARPANET,  between UCL in London, ISI in Los
   Angeles, and COMSAT in  Washington  D.C..  The  Network
   Independent File Transfer Protocol (NIFTP, [9]) is used
   to transfer the image data.   This  protocol  has  been
   implemented  on LSI under MOS [10].  In addition, we at
   UCL have put NIFTP on an ARPANET  TOPS-20  host,  which
   can  act  as  an Internet File Forwader (IFF).  In this
   case, TCP/IP ([28], [29]) is employed as the underlying
   transport   service.   Since   TCP   provides  reliable
   communication channels, the  provision  of  checkpoints
   and  error-recovery  procedures are not included in our
   NIFTP implementations.
     In  the  X25  network,  the  transport  procedure  is
   NITS/X25   ([25],   [26]).    Though  pictures  can  be
   transferred to the X25 networks, no  experimental  work
   has been done, because:
    (1) There is at present no  collaborative  partner  on
        these networks.
    (2) The LSI-11, on which our  system  is  implemented,
        has no direct connection to these networks.
     Locally,  image  data  can  be  transmitted  to   the
   PDP11-44s   running  the  UNIX  time-sharing  operating
   system. At present, the SCP ring-driver  software  uses
   permanent   virtual  circuits  (PVCs)  to  connect  the
   various computers on the ring.
   4.4 File System
     A file system has been designed, based on  the  AED62
   double  density  floppy  disk, for use under MOS. It is
   itself implemented as  a  MOS  process  supporting  the
   Clean  and  Simple  interface.  The description of this
   task, fs(fax), can be found in Appendix 2.
  1. 31 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     In a command string, the file system  task  can  only
   serve  as  either  data  source  or data sink. In other
   words, it can only appear at the first or last position
   on  a  command  string.  In  the  former case, the file
   specified is to be  read,  while  the  file  is  to  be
   written in the latter case.
     Three access modes are allowed which are:
  • Read a file
  • Create a file
  • Append a file
     The file name and access mode are  specified  as  the
   open parameters.
     Let us consider an example.  If a document is  to  be
   read  on  the  facsimile  machine  and  the data stream
   created is to be stored on the file system, the command
   string required is:
           fax"r|fs"c,doc
   where:  fax - interface task for facsimile machine
           r   - read from facsimile machine
           fs  - file system task
           c   - create a new file
           doc - the name of the file to be created.
     In order to dump a  file,  a  task  process  od()  is
   provided  which  works  as  a  data  sink  in a command
   string.
   4.5 Data Structure
     Facsimile  image  data  is  created  using  a   high-
   resolution raster scanner, so that the original picture
   can  be  reproduced  faithfully.  The  facsimile   data
   represents  binary  images,  in  monochrome,  with  two
   levels of intensity, belonging  to  the  data  type  of
   bit-mapped graphics.
     The simplest representation is  the  bit-map  itself.
   The bits, each of which corresponds to a single picture
   element, are arranged in the  same  order  as  that  in
   which  the original picture is scanned, 1s standing for
  1. 32 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   black pixels and 0s for white ones. Operations  on  the
   picture are easily carried out. For example, two images
   represented  in  the  bit-map  format  can  be   merged
   together  by  using  a  simple  logic OR operation. Any
   specific  pixel  can   be   retrieved   by   a   simple
   calculation. However, its size is usually large because
   of  the  high  resolution.   This   makes   it   almost
   unrealistic for storage or transmission.
     Facsimile image data should therefore  be  compressed
   to reduce its redundancy, so that the efficient storage
   and transmission can be achieved.
     Run-length encoding is a useful  compression  scheme.
   Instead of the pattern, the counts of consecutive black
   and white runs are used to represent the image.
     Vector representation, in which the  run-lengths  are
   coded  as  integers  or  bytes,  is  a  useful internal
   representation of images. Not  only  is  it  reasonably
   compressed,  but  it is also quite easy for processing.
   Chopping, scaling and mask-scanning are examples of the
   processing   operations   which   may   be   performed.
   Furthermore, a conversion between different compression
   schemes  may  have to be carried out in such a way that
   the data is first decompressed into the  vector  format
   and  then recompressed. The difficulty in retrieval can
   be overcome by means of line  index,  which  gives  the
   pointers to each lines of the image.
     A higher compression rate leads to a  more  efficient
   transmission.  But  this  is  at the expense of ease of
   processing.  An example of this is the use  of  Huffman
   Code  in  the  CCITT  1-dimensional compression scheme.
   While the data can be compressed more  efficiently,  it
   is rather difficult to manipulate the data direcltly.
     Taking the correlation between  adjacent  lines  into
   account,  2-dimensional compression can achieve an even
   higher   compression    rate.    CCITT    2-dimensional
   compression  and  the  DACOM facsimile machine use this
   method.
     It is desirable to integrate  facsimile  images  with
   other  data types, such as text and geometric graphics;
   the  structure  of  these  other  types  must  then  be
   incorporated  in  the  system.  At  present,  only text
   structure  is  available,  while  the   structure   for
   geometric graphics is a topic for the further study.
  1. 33 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     In  the  facsimile   system,   the   following   data
   structures    are    supported.    The    corresponding
   descriptions, if any, are listed as well and  they  can
   be found in Appendix 3 (except of dacom(device)).
   type    structure       compression     description
   bit-map  bit-map               -              -
           vector          1D run-length   vector(fax)
           dacom block     2D run-length   dacom(device)
           CCITT T4        1D run-length   t4(fax)
                           2D run-length   t4(fax)
   text    text                  -         text(fax)
     As an  internal  data  structure,  vector  format  is
   widely  used  for data transfer between task processes.
   The set of interface  routines  has  been  extended  by
   introducing  two subroutines, namely getl() and putl(),
   which read and write line vectors directly through  the
   Clean  and  Simple interface. These two routines can be
   found in Appendix 3 (getl(fax) and putl(fax))
     In order to check the validity of a  vector  file,  a
   check task process check() is provided which works as a
   data sink in a command string. It  can  also  dump  the
   vector elements of the specific lines.
   4.6 Data Conversion
     In order to convert one data structure into  another,
   several conversion modules are provided in this system.
   These modules fall into two categories, task  processes
   and  subroutines.  The task processes are MOS processes
   which can only be used in the environment described  in
   this note, while the subroutines which are written in c
   and compatible under UNIX are more generally usable.
     Character strings  or  text  can  be  converted  into
   vector  format,  so  that an integrated image combining
   picture and text can be formed.
     The following table lists these  conversion  modules,
   including  their  functions and descriptions (which can
   be found in Appendix 3).
  1. 34 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   module  type          from          to      description
   decomp  process       dacom         vector   decomp(fax)
   recomp  process       vector        dacom    recomp(fax)
   ccitt   process       vector        t4       ccitt(fax)
                         t4            vector
   bitmap  subroutine    vector        bitmap    bit-map(fax)
   tovec   subroutine    bitmap        vector    tovec(fax)
   ts      subroutine    ASCII string  vector   ts(fax)
   string  process       ASCII string  vector   string(fax)
   tf      process       text          vector   tf(fax)
     Since each DACOM block contains a  Cyclic  Redundancy
   Check  (CRC)  field,  the  system supplies a subroutine
   crc()  to  calculate  or  check  the  CRC  code.   (see
   crc(fax))
     If a vector file  is  to  be  printed  on  the  DACOM
   facsimile   machine,  the  image  data  should  be  re-
   compressed into the DACOM-block  format,  the  required
   command string being shown below.
   fs"e,pic|recomp|fax"w
   where   fs     - file system task
           e      - read an existing file
       ic    - file name
           recomp - re-compression task
           fax    - interface task for facsimile machine
           w      - print an image on facsimile machine
   4.7 Image Manipulation
     Four processing task processes are  provided  in  the
   system.  These are:
    (1) Chop, which applies a defined window to the  input
        image.
    (2) Scale, which enlarges or shrinks the  input  image
        to the defined dimensions.
    (3) Merge, which puts the input image on the specified
        area of a background image.
  1. 35 -

UCL FACSIMILE SYSTEM INDRA Note 1185

    (4) Clean, which removes the noise on the input image.
     The Clean and  Simple  interfaces  are  supported  in
   these processing tasks so that the tasks can be used in
   command strings.  However, these tasks can  be  neither
   source  nor  sink in a command string.  The data format
   of their input and output is vector.
     For example, a facsimile page can be cleaned and then
   printed  on  the facsimile machine. Note that the image
   data must be recompressed  before  being  sent  to  the
   facsimile  machine. If the original data is the form of
   DACOM  block,  it  has  to  be  decompressed   as   the
   processing   tasks   only  accept  line  vectors.   The
   required command string is shown below.
   fs"e,page|clean|recomp|fax"w
   where   fs     - file system task
           e      - read an existing file
           page   - file name
           clean  - cleaning task
           recomp - re-compression task
           fax    - interface task for facsimile machine
           w      - print an image on facsimile machine
     The descriptions of these  processing  tasks  can  be
   found in Appendix 2 (chop(fax), scale(fax), merge(fax),
   and clean(fax)).
     In tasks 'chop' and  'merge',  a  window  is  set  by
   giving  the coordinates of its vertices. However, it is
   usually rather difficult for a human user to decide the
   exact  coordinates.  The  system  supplies a subroutine
   choice() which specifies a rectangular subsection of an
   image  by  interactive  manipulations  of a rectangular
   subsection  on  the  screen  of  the  Grinnell  display
   displaying the image.  It provides a set of interactive
   commands whereby a user can intuitively choose an  area
   he  is interested in. Note that this subroutine must be
   called by a MOS process and the Grinnell  display  must
   be included in the system.
     By means of these image processing modules, the image
   editing  described  in  section 2.4 can be carried out.
   Let us consider an example. An image abstracted from  a
   picture  'a'  is  to be merged onto a specified area of
   another picture 'b'. First of all, the two pictures 'a'
  1. 36 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   and 'b' should be displayed on the left half and  right
   half  of  the screen, respectively. Assume that the two
   pictures are standard DACOM pages whose dimensions  are
   1726x1200.  They have to be shrunk to fit the dimension
   of the half screen (256x512).  Note that  if  the  data
   format  is not vector, conversion should be carried out
   first.  the required command strings are:
 e,a|scale"1726,1200,256,512|grinnell"0,511,255,0,z,g
   fs"e,b|scale"1726,1200,256,512|grinnell"256,511,511,0,z,b
   where   fs            - file system task
           e             - read an existing file
           a             - file name
           b             - file name
           scale         - scale task
           1726,1200     - old dimension
           256,512       - new dimension
           grinnell       - grinnell display interface task
           0,511,255,0   - presentation area (the left half)
           256,511,511,0 - presentation area (the right half)
           z             - zero write mode
           g             - green
           b             - blue
     In an application process, the subroutine choice() is
   called in the following ways for the user to choose the
   areas on both pictures.
  1. 37 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   choice(r, 1726, 1200, 1, 0, 0);
           /* choice the area on 'a' */
           /* r    - red
              1726 - width of the original picture
              1200 - height of the original picture
              1    - left half of the screen
              0    - the subsection can be of any width
              0    - the subsection can be of any height
            */
   choice(r, 1726, 1200, 2, 0, 0);
           /* choice the area on 'b' */
           /* r    - red
              1726 - width of the original picture
              1200 - height of the original picture
              2    - right half of the screen
              0    - the subsection can be of any width
              0    - the subsection can be of any height
            */
     When the user finishes editing,  the  coordinates  of
   the  chosen  rectangular areas are returned. An example
   is given in the table below.  The  widths  and  heights
   listed  in  the  table are actually calculated from the
   coordinates returned and they indicate that the  source
   image has to be enlarged to fit its destination.
            (0, 0)
              +-------------------------------> x
              |
              |  (x0, y0)     w
              |     +--------------------+
              |     !                    !
              |     !                    !
              |     !                    ! h
              |     !                    !
              |     !                    !
              |     +--------------------+
              |                       (x1, y1)
              V
              y
   original   x0      y0      x1      y1      w       h
      a       30      40     100     120      70      80
      b      100     100    1100    1100    1000    1000
  1. 38 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     At this stage, our final  goal  can  be  achieved  by
   performing  a  job  specified below. It is assumed that
   the result image is to be stored as a new file 'c'.
   fs"e,a|chop"30,40,100,120|scale"70,80,1000,1000
       |merge"b,0,100,100,1100,1100|fs"c,c
   where   fs                - file system task
           e                 - read an existing file
           a                 - file name
           chop              - chop task
           30,40,100,120     - the area to be abstracted
           scale             - scale task
           70,80             - old dimension
           1000,1000         - new dimension
           merge             - merge task
           b                 - file name of the background image
           0                 - to be overlaid
           100,100,1100,1100 - the area to be overlaid
           fs                - file system task
           c                 - create a new file
           c                 - the name of the file to be
                               created
   4.8 Data Transmission
     In  order  to  transmit  facsimile  image  data  over
   computer  networks,  using the configuration of Fig. 1,
   the Network Independent File Transfer Protocol  [9]  is
   implemented as a MOS task process, the Clean and Simple
   interface of section 3.3  being  supported  [10].  Thus
   this  module  can be used in a command string directly.
   In this case, the module always works in the  initiator
   mode,  though the server mode is supported as well. Its
   description can be found in Appendix 2 (ftp(fax)).
     As  a  network-independent  protocol,  it  employs  a
   transport  service  to communicate across the networks.
   The Clean and Simple interface is  also  used  for  the
   communication  between the module and transport service
   processes.
     Suppose that an image file stored in  a  remote  file
   system is to be printed on the local facsimile machine.
   Assume that the data is  transmitted  via  the  ARPANET
   [21],  Transport Control Protocol (TCP) [28] being used
   as the underlying transport service. As  was  described
  1. 39 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   before, since the  delay  caused  by  the  network  may
   result  in  a  time-out on the local facsimile machine,
   the job should be divided into two subjobs.
    (1) The remote file  is  transmitted  by  using  NIFTP
        module.   However,  instead  of  being  put on the
        facsimile machine directly, the received  data  is
        store in a temporary file.
        ftp"r,b,ucl,fax,pic;tcp:1234,10,3,3,42,4521|fs"c,tmp
        where   ftp - NIFTP task
                t   - receive
                b   - binary
                ucl - remote user name
                fax - remote password
                pic - remote file name
                tcp - transport service process
                parameters for the transport service:
                    1234      - local channel number
                    10,3,3,42 - remote address
                    4521      - channel reserved for the
                                remote server
                fs  - local file system task
                c   - create a new file
                tmp - the name of the file to be created
    (2) The temporary file is read and the image  is  sent
        to  the facsimile machine for printing. Here it is
        assumed the data received is in the form of  DACOM
        block so that no conversion is needed.
        fs"e,tmp|fax"w
        where   fs     - file system task
                e      - read an existing file
                tmp    - file name
                fax    - interface task for facsimile machine
                w      - print an image on facsimile machine
     We are able to  exchange  image  data  with  ISI  and
   COMSAT.  At present DACOM block is the only format that
   can be used as  all  the  three  participants  in  this
   experiment  possess  DACOM  facsimile  machines  and no
  1. 40 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   other data format is available in both ISI and  COMSAT.
   However,  it  is  the  intention  of the ARPA-Facsimile
   community to adopt the CCITT standard for future  work.
   As mentioned earlier, UCL already has this facility.
     Above NIFTP, a simple protocol was  used  to  control
   the  transmission  of facsimile data. In this protocol,
   the format of a facsimile  data  file  was  defined  as
   follows:  Each  DACOM  block was recorded with a 2-byte
   header at the front. This  header  was  composed  of  a
   length-byte   indicating   the   length  of  the  block
   (including the header) and a code-byte  indicating  the
   type  of  the  block.  This  is  shown in the following
   diagram.
           |<--- header ---->|<------ 74 bytes ------->|
           +--------+--------+-------------------------+
           ! length !  code  !       DACOM block       !
           +--------+--------+-------------------------+
     The Length-byte is 76 (decimal) for all DACOM blocks.
   The  code-byte for a setup block is 071 (octal) and 072
   for a data block. A  special  EOP  block  was  used  to
   indicate  the  end  of  a page. This block had only the
   header with the length-byte set to 2 and the  code-byte
   undefined.  A facsimile data file could contain several
   pages, which were separated by EOP blocks.
   5. CONCLUSION
   5.1 Summary
     Though techniques  for  facsimile  transmission  were
   invented  in  1843,  it  was not until the recent years
   that integration with  computer  communication  systems
   gave rise to "great expectation".  The system described
   in  this  note   incarnates   the   compatibility   and
   flexibility of computerised facsimile systems.
     In this system, facsimile no longer refers simply  to
   the  transmission device, but rather to the function of
   transferring hard copy from one place to another.   Not
   only  does  the  system  allow  for  more  reliable and
   accurate document transmission over  computer  networks
   but  images  can  also  be  manipulated electronically.
   Image is converted from one  representation  format  to
   another,  so that different makes of facsimile machines
   can communicate with each other.  It is possible for  a
  1. 41 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   picture to be presented on different  bit-map  devices,
   e.g.  TV-like  screen,  as it can be scaled to overcome
   the incompatibilities.  Moreover, the  system  provides
   windowing   and   overlaying   facilities   whereby   a
   sophisticated editor can be supported.
     One of the most important aspects of this  system  is
   that   text   can  be  converted  into  its  bit-mapped
   representation format  and  integrated  with  pictures.
   Geometric  graphics  could  also  be  included  in  the
   system. Thus, the facsimile  machine  may  serve  as  a
   printer  for  multi-type  documents.  It  is clear that
   facsimile  will  play  an  important  role  in   future
   information processing system.
     As far  as  the  system  per  se  is  concerned,  the
   following  advantages  can  be  recognised.  Though our
   discussion is concentrated  on  the  facsimile  system,
   many  features  developed  here  apply  equally well to
   other information-processing systems.
    (1)  Flexibility:  The  user  jobs   can   be   easily
        organised.  The  only  thing  to  be done for this
        purpose is to  make  the  logical  links  for  the
        appropriate task processes.
    (2) Simplicity: The interface routines are responsible
        for  the  operations  such  as signal handling and
        buffer management.  By avoiding this  burden,  the
        implementation  of the task processes becomes very
        "clean and simple".
    (3) Portability: The interface routines also makes the
        task   processes   totally   independent   of  the
        operating environment.  Only these routines should
        be modified if the environment were changed.
    (4) Ease of extension: The power of the system can  be
        simply  and infinitely extended by adding new task
        processes.
    (5) Distributed  Environment:  This  approach  can  be
        easily  extended  to  a  distributed  environment,
        where limitless hardware  and  software  resources
        can be provided.
   5.2 Problems
     As discussed earlier, the network we were  using  for
   the  experimental  work was not designed for image data
  1. 42 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   transmission.  The data transfer  is  so  slow  that  a
   time-out may be caused on the facsimile machine. Though
   this problem was solved by means of local buffering and
   pictures  were successfully exchanged over the network,
   the slowness is rather  disappointing  because  of  the
   quantity of image data. The measurement showed that the
   throughput was around 500 bits/sec. In other words,  it
   took  at  least  5 minutes to transfer a page. This was
   caused by the network but not our system. The situation
   has been improved recently. However, It is nevertheless
   required that more  efficient  compression  schemes  be
   developed.
     At present, the system must be directly  attached  to
   the  network to be accessed. However, the network ports
   are much demanded, so that frequent reconfiguration  is
   required.
     The facsimile system can be  connected  only  to  the
   local  network,  the  Cambridge Ring, while the foreign
   networks are connected via gateways to the  ring.  This
   is shown in Fig. 12. Now the X25 network is attached to
   the Ring via an X25 gateway, XG [25], while  SATNET  is
   connected by another gateway, SG [25]. Both network are
   at the transport level; XG and SG support the  relevant
   transport  procedures.  In  the  case  of  XG,  this is
   NITS/X25 ([26], [27]); in the case  of  SATNET,  it  is
   TCP/IP ([28], [29]).
   UCL facsimile
     system          - - - - - - - -
   +--------+      /                 \      +------+
   !        ! ----    Cambridge Ring   ---- !  PE  !
   +--------+      \                 /      +------+
                     - - - - - - - -            |
                       /         \              |
                 +------+       +------+        |
                 !  XG  !       !  SG  ! --- SATNET
                 +------+       +------+
                 /       \
               PSS    SERC NET
        Fig. 12  Schematic of UCL network connection
     When the network software runs in the same machine as
   the   application   software,   the  Clean  and  Simple
   interface of section  3.5  was  used  as  an  interface
   between  the  modules.  When  the  gateway software was
   removed to a separate machine, an Inter-Processor Clean
  1. 43 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   and  Simple  [30]  was   required.    The   appropriate
   transport   process  is  transferred  to  the  relevant
   gateway, and appropriate facilities are implemented for
   addressing   the   relevant   gateway.  Otherwise,  the
   software has to be little  altered  to  cater  for  the
   distributed case.
     In our experimental work, the following problems were
   also encountered.
    (1) The primary memory of the LSI-11 is so small  that
        we  cannot  build  up  a system to include all the
        modules we have developed.  In order  to  transfer
        an  edited picture using the NIFTP module, we have
        to first  load  an  editor  system  to  input  and
        process  the  picture, and then an NIFTP system is
        then loaded to transmit it.
    (2) The execution of  an  image  processing  procedure
        becomes  very  slow. For example, it takes several
        minutes to shrink a picture to fit the  screen  of
        the  Grinnell  display.  This  prevents the system
        from being widely used in its present form.
    (3) As secondary storage, floppy disks  are  far  from
        adequate  to keep image data files. At present, we
        have two double-density floppy  disk  drives,  the
        capacity  of  each  disk  being  about 630K bytes.
        However, an image page contains at least 50K bytes
        and,  sometimes,  this number may be doubled for a
        rather complex picture.  Only a limited number  of
        pages can be stored.
     On the other hand, in our  department,  we  have  two
   PDP11-44s   running  UNIX  together  with  large  disks
   supplying abundant file storage. Their processing speed
   is  much  higher  than  that of the LSIs. The UNIX file
   system  supports   a   very   convenient   information-
   management environment. This inspired the idea that the
   UNIX file system could pretend  to  be  a  file  server
   responsible for storing and managing the image data, so
   that all the processing tasks may  be  carried  out  on
   UNIX. Not only does this immediately solve the problems
   listed above, but the following  additional  advantages
   immediately accrue.
    (1) UNIX provides a  far  better  software-development
        environment than LSI MOS ever can or will.
    (2) The facsimile service can be enhanced to  be  able
  1. 44 -

UCL FACSIMILE SYSTEM INDRA Note 1185

        to support many users at a time.
    (3) The UNIX file system is so sophisticated that more
        complex data entities can be handled.
     In  fact  the  44s  and  the  LSI-11,  to  which  the
   facsimile  machine  and  Grinnell display are attached,
   are  all  connected  to  the  UCL  Cambridge  Ring.   A
   distributed  processing  environment  can  be  built up
   where a job in one computer can be initiated by another
   and  then the job will be carried out by cooperation of
   both computers.
     In such  a  distributed  system,  the  LSI-11  micro-
   computer,   together   with   the   facsimile  machine,
   constitutes  a   totally   passive   facsimile   server
   controlled  by  a  UNIX  user.  A  page  is read on the
   facsimile machine and the image data stream produced is
   transmitted to the UNIX via the ring. The image data is
   stored  as  a  UNIX  file  and  may  be  processed   if
   necessary.  It  can  also  be  sent via the ring to the
   facsimile server where it  will  be  reprinted  on  the
   facsimile machine.
     In order to build up such a distributed  environment,
   IPCS  [30] is far from adequate for this purpose, as it
   does not provide any facility for a remote  job  to  be
   organised.  In  our  system, the task controller can be
   modified so that the command strings  can  be  supplied
   from  a remote host on the network. Having accepted the
   request, the task  controller  organises  the  relevant
   task  chain and the requested job is executed under its
   control.  The execution  of  the  distributed  job  may
   require  synchronisation  between  the  two  computers.
   These problems are discussed in detail in [31].
     Generally speaking, a distributed system based  on  a
   local network, which supplies cheap, fast, and reliable
   communication, could be the ultimate  solution  of  the
   operational problems discussed in this section. In such
   a system, different system operations are  carried  out
   in the most suitable places.
     For the time being, only a  procedure-oriented  task-
   control  language  is  available  in  this system.  The
   command string of the fitter  can  be  typed  from  the
   system  console  directly,  the corresponding job being
   organised and executed.  Theoretically, this  is  quite
   enough   to  cope  with  any  requirement  of  a  user.
   However,  when  the  job  is  complex,  command  typing
   becomes very tedious and prone to error.
  1. 45 -

UCL FACSIMILE SYSTEM INDRA Note 1185

     Above the task-controller, a job-controller layer  is
   required  which  provides  a  problem-oriented language
   whereby the user can easily put forward his requirement
   to  the  system.  On receipt of such a command, the job
   controller translates it into a command string  of  the
   task  controller  and  passes  the  string  to the task
   controller so  that  operation  request  can  be  done.
   Sometimes,  one  job  has  to  be  divided into several
   subjobs, which are to be dealt  with  separately.   The
   job  controller  should  be  also  responsible for high
   level calculation and management, so that the user need
   not be concerned with system details.
     In the  system  supporting  facsimile  service  under
   UNIX,  a  set  of high-level command is provided, while
   the command  strings  for  the  facsimile  station  are
   arranged automatically and they are totally hidden from
   a UNIX user.
   5.3 Future Study
     At the next stage, our attention should be moved to a
   higher-level,  more sophisticated system which supports
   a multi-type environment. In such a  system,  not  only
   does   the  facsimile  machine  work  as  an  facsimile
   input/output device, but it should also play  the  role
   of  a  printer  for  the  multi-type  document. This is
   because other data types, e.g. coded character text and
   geometric  graphics  can  be easily converted into bit-
   mapped graphics format which the facsimile  machine  is
   able to accept.
     First of all, a data structure should be designed  to
   represent  multi-type  information.  In  a  distributed
   environment, such a structure should be understood  all
   over  the  system,  so  that multi-media message can be
   exchanged.
     In a future  system,  different  services  should  be
   supported,   including  viewdata,  Teletex,  facsimile,
   graphics,  slow-scan  TV  and  speech.  The  techniques
   developed  for facsimile will be generalised for use of
   other bit-mapped image representations, such  as  slow-
   scan TV.
     To improve the performance of the  facsimile  system,
   we  are  investigating  how  we  could use an auxiliary
   special purpose processor to perform some of the  image
   processing   operations.   Such  a  processor  will  be
   essential for the higher data rate  involved  in  slow-
  1. 46 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   scan TV.
  1. 47 -

UCL FACSIMILE SYSTEM INDRA Note 1185

                          Reference
    [1] P. T. Kirstein, "The Role of Facsimile in Business
        Communication", INDRA Note 1047, Jan. 1981.
    [2]  T.  Chang,  "A  Proposed  Configuration  of   the
        Facsimile station", INDRA Note 922, May, 1980.
    [3] T.  Chang,  "Data  Structure  and  Procedures  for
        Facsimile Signal Processing", INDRA Note 923, May,
        1980.
    [4] S. Treadwell,  "On  Distorting  Facsimile  Image",
        INDRA Note No 762, June, 1979.
    [5] M. G. B. Ismail and R.  J.  Clarke,  "A  New  Pre-
        Processing   Techniques   for   Digital  Facsimile
        Transmission", Dept.  of  Electronic  Engineering,
        University of Technology, Loughborough.
    [6]  T.  Chang,  "Mask  Scanning  Algorithm  and   Its
        Application", INDRA Note 924, June, 1980.
    [7] M. Kunt and O. Johnsen, "Block Coding of Graphics:
        A  Tutorial  Review",  Proceedings  of  the  IEEE,
        special issue on  digital  encoding  of  graphics,
        Vol. 68, No 7, July, 1980.
    [8]  T.  Chang,   "Facsimile   Data   Compression   by
        Predictive  Encoding",  INDRA  Note  No  978, May.
        1980.
    [9] High Level Protocol Group, "A Network  Independent
        File  Transfer  Protocol",  HLP/CP(78)1, alos INWG
        Protocol Note 86, Dec. 1978.
   [10] T. Chang, "The Implementation of NIFTP on LSI-11",
        INDRA Note 1056, Mar. 1981.
   [11] T. Chang, "The  Design  and  Implementation  of  a
        Computerised  Facsimile  System",  INDRA  Note No.
        1184, Apr. 1981.
   [12] T. Chang, "The Facsimile Editor", INDRA Note 1085,
        Apr. 1981.
   [13]  K.  Jackson,  "Facsimile   Compression",  Project
        Report,  Dept.  of  Computer  Science,  UCL, June,
        1981.
  1. 48 -

UCL FACSIMILE SYSTEM INDRA Note 1185

   [14] R. Cole and S. Treadwell, "MOS User Guide",  INDRA
        Note 1042, Jan. 1981.
   [15] CCITT,  "Recommendation  T.4,  Standardisation  of
        Group   3   Facsimile   Apparatus   for   Document
        Transmission", Geneva, 1980.
   [16]  "DACOM  6450  Computerfax  Transceiver   Operator
        Instructions", DACOM, Mar. 1977.
   [17] "AED 6200LP Floppy Disk Storage System", Technical
        Manual,  105499-01A,  Advanced Electronics Design,
        Inc. Feb. 1977.
   [18] "The User Manual for Grinnelll Colour Display".
   [19] D. R. Weber,  "An  Adaptive  Run  Length  Encoding
        Algorithm", ICC-75.
   [20] R. Braden and P. L. Higginson, "Clean  and  Simple
        Interface  under  MOS",  INDRA Note No. 1054, Feb.
        1981.
   [21] L. G. Roberts et al, "The ARPA Computer  Network",
        Computer  Communication  Networks,  Prentice Hall,
        Englewood, pp485-500, 1973.
   [22] I. M. Jacobs et  al:  "General  Purpose  Satellite
        Network",   Proc.   IEEE,   Vol.   66,   No.   11,
        pp1448-1467, 1978.
   [23] J.  W.  Burren  et  al,  "Design  fo  an  SRC/NERC
        Computer   Network",   RL   77-0371A,   Rutherford
        Laboratory, 1977.
   [24] P. T. F.  Kelly,  "Non-Voice  Network  Services  -
        Future     Plans",     Proc.     Conf.    Business
        Telecommunications, Online, pp62-82, 1980.
   [25] P. T. Kirstein, "UK-US  Collaborative  Computing",
        INDRA Note No. 972, Aug. 1980.
   [26] "A Network  Independent  Transport  Service",  PSS
        User   Forum,  Study  Group  3,  British  Telecom,
        London, 1980.
   [27] CCITT, Recommendation X3,  X25,  X28  and  X29  on
        Packet Switched Data Services", Geneva 1978.
   [28]  "DoD  Standard  Transmission  Control  Protocol",
        RFC761,  Information  Sciences  Inst.,  Marina del
  1. 49 -

UCL FACSIMILE SYSTEM INDRA Note 1185

        Rey, 1979.
   [29]  "DoD   Standard   Internet   Protocol",   RFC760,
        Information Sciences Inst., Marina del Rey, 1979.
   [30] P. L. Higginson, "The Orgainisation of the Current
        IPCS System", INDRA Note No. 1163, Oct. 1981.
   [31] T. Chang, "Distributed Processing for  LSIs  under
        MOS", INDRA Note No. 1199, Jan. 1982.
  1. 50 -

UCL FACSIMILE SYSTEM INDRA Note 1185

                   Appendix I: Devices

AED62(DEV) AED62(DEV)

NAME

   aed62 - double density floppy disk

SYNOPSIS

   DCT aed62
   setdct("aed62", 0170, 0170450, 0170450,
           aedini, aedsio, aedint, 0);

DESCRIPTION

   The Double Density disks contain 77 tracks numbered  from  0
   to  76.  There  are 16 sectors (sometimes called blocks) per
   track, for a total of 1232 sectors on each side of the disk.
   These  are  numbered  0  to  1231.  Each sector contains 512
   bytes, for a total of 630,784 bytes  on  each  side  of  the
   floppy.
   Only one side of the floppy can be accessed at a time. There
   is  only one head per drive, and it is located on the under-
   side of the disk. To access the other side, the disk must be
   manually removed and inserted the other way up.
   Each block is actually two blocks on the disk:  an  adddress
   ID  block  and the data block.  The address ID block is used
   by the hardware and contains the  track  number,  the  block
   number and the size of the data block that follows.  When an
   operation is to take place, the seek mechanism first locates
   the  block  by  reading  the address ID blocks and literally
   'hunting' for the correct one. It will  hunt  for  up  to  2
   seconds before reporting a failure.
   Both the address ID and the data blocks are  followed  by  a
   checksum word that is maintained by the hardware and is hid-
   den from the user. On writing, the  checksum  is  calculated
   and  appended  to the block. On reading it is verified (both
   on reading the ID and data blocks) and any error is reported
   as  a  Data Check. No checking on the data block takes place
   on a write, and the hardware has no idea if it  was  written
   correctly. The only way to verify it is to read it.
   Although there are two drives in the unit,  they  cannot  be
   used  simultaneously. If an operation is in progress on one,
   no access can be made to the other until the first operation
   is  complete. The driver will queue requests for both drives
   however, and ensure that are performed in order.
   The MOS driver is called aed62.obj. It operates on the  fol-
   lowing IORB entries:

AED62(DEV) AED62(DEV)

   irfnc
        The operation to be performed, as follows:
                        0 - Read
                        1 - Write
                        2 - Verify
                        3 - Seek
        Read and Write cause data to be transferred to and from
        disk.  Verify does a hardware read without transferring
        the data to memory and is used for verifying  that  the
        data  can be successfully read. The checksum at the end
        of  the  block  of  each  sector  is  verified  by  the
        hardware.  The  seek  command  is used to move the disk
        heads to a specified track.
   irusr1
        The drive number. Only Zero or One is accepted. This is
        matched  against the number dialed on the drive. If the
        number is specified  on  both  drives,  or  neither,  a
        hardware error will be reported.
   irusr2
        The Sector or Block Number. Must be in the range  0  to
        1231 inclusive.  irusr2 specifies the block number that
        the transfer is to begin at for Read and Write, the be-
        ginning  of  the  verified area for the Verify command,
        and the position of the head for the Seek  command.  In
        the  latter  case  the  head  will be positioned to the
        track that contains the block.
   iruva
        This specifies the data  adress,  which  must  be  even
        (word  boundary).   If an odd address is given, the low
        order bit is set to zero to make it even. Not  required
        for the Seek or Verify commands.
   irbr
        Transfer length as a positive number of bytes. Not  re-
        quired for the seek command, bit IS used by Verify com-
        mand so that the correct number of blocks may be  veri-
        fied.  The disk is only capable of transferring an even
        number of bytes. If an odd length is given the low ord-
        er  bit  is made zero to reduce the length to the lower
        even value.  The length is NOT restricted to the sector
        size  of  512 bytes. If the length is greater than 512,
        successive blocks are read/written until  the  required
        transfer

AED62(DEV) AED62(DEV)

        length has been satisfied. If the length is not an  ex-
        act  multiple  of  512 bytes, only the specified length
        will be read/written. Note  that  the  hardware  always
        reads  and  writes  a  complete sector, so specifying a
        shorter length on a read will cause  the  remainder  of
        the  block to be skipped. On a write, the hardware will
        repeat the last specified  word  until  the  sector  is
        full.
   The driver will attempt to recover  from  all  soft  errors.
   There  is no automatic write/read verify as on mag tapes, so
   that data that is incorrectly written will not  be  detected
   as such until a read is attempted. For this reason, the ver-
   ify feature can be used (see above) to force the checking of
   written  data.  When an error is detected while performing a
   read, the offending block will be re-read up to 16 times and
   disk  resets  will be attempted during this time too. If all
   fails a hardware error indication is returned to  the  user.
   Other errors possible are Protection Error (attempt to write
   to a read-only disk) and User Error,  which  indicates  that
   the  parameters  in  the IORB were incorrect. Errors such as
   there being no disk loaded, or the drive door being open are
   NOT  detectable  by the program. The interface sees these as
   Seek Errors (i.e. soft errors), and thus the driver will re-
   try  several times before returning a Hardware Error indica-
   tion to the user. It should be noted that error recovery can
   take  a  long  time. As mentioned above, there is a 2 second
   delay before a seek error is reported by the  hardware,  for
   instance.

GRINNELL(DEV) GRINNELL(DEV)

NAME

   grinnell - colour display

SYNOPSIS

   DCT grndout
   setdct("grndout", 03000, 0172520, 0172522,
           grnoi, grnot, grnoti, &grndin);
   DCT grndin
   setdct("grndin", 03000, 0172524, 0172526,
           grnoi, grnot, grnoti, &grndout);

DESCRIPTION

   The Grinnell colour display has a screen  of  512x512  pels.
   Three colours (red, green and blue) can be used, but no grey
   scale is supported.  Three  graphics  modes  are  available.
   These are:
    (1) Alphanumeric: The input ASCII characters are  displayed
        at the selected positions on the screen.
    (2) Graphic: Basic geometric elements,  such  as  line  and
        rectangle, are drawn by means of graphics commands.
    (3) Image: The input data is interpreted as  bit  patterns,
        the corresponding images being illustrated.
   The values used to construct commands are described  in  the
   Grinnell User Manual. They are also listed below.
    #define LDC     0100000   /* Load Display Channels */
    #define LSM     0010000   /* Load Subchannel Mask */
    #define   RED   0000010   /* Read Subchannel */
    #define   GREEN 0000020   /* Green subchannel */
    #define   BLUE  0000040   /* Blue subchannel */
    #define WID     0000000   /* Write Image Data */
    #define WGD     0020000   /* Write Graphic Data */
    #define WAC     0022000   /* Write AlphanumCh */
    #define LWM     0024000   /* Load Write Mode */
    #define   REVERSE  0200   /* Reverse Background */
    #define   ADDITIVE 0100   /* Additive (not Replace) */
    #define   ZEROWRITE 040   /* Dark Write */
    #define   VECTOR    020   /* Select Vector Graph */
    #define   DBLEHITE  010   /* Double Height write */
    #define   DBLEWIDTH 004   /* Double Width write */
    #define   CURSORAB  002   /* Cursor (La+Lb,Ea+Eb) */

GRINNELL(DEV) GRINNELL(DEV)

    #define   CURSORON  001   /* Cursor On */
    #define LUM     0026000   /* Load Update Mode */
    #define   Ec        001   /* Load Ea with Ec */
    #define   Ea_Eb     002   /* Load Ea with Ea + Eb */
    #define   Ea_Ec     003   /* load Ea with Ea + Ec */
    #define   Lc        004   /* Load La with Lc */
    #define   La_Lb     010   /* Load La with La + Lb */
    #define   La_Lc     014   /* Load La with La + Lc */
    #define   SRCL_HOME 020   /* Scroll dsiplay to HOME */
    #define   SRCL_DOWN 040   /* Scroll down one line */
    #define   SCRL_UP   060   /* Scroll up one line */
    #define ERS     0030000   /* Erase */
    #define ERL     0032000   /* Erase Line */
    #define SLU     0034000   /* Special Location Update */
    #define   SCRL_ZAP 0100   /* unlimited scroll speed */
    #define EGW     0036000   /* Execute Graphic Write */
    #define LER     0040000   /* Load Ea relative */
    #define LEA     0044000   /* Load Ea */
    #define LEB     0050000   /* Load Eb */
    #define LEC     0054000   /* Load Ec */
    #define LLR     0060000   /* Load La Relative */
    #define LLA     0064000   /* Load La */
    #define LLB     0070000   /* Load Lb */
    #define LLC     0074000   /* Load Lc */
    #define   LGW     02000   /* perform write */
    #define NOP     0110000   /* No-Operation */
    #define SPD     0120000   /* Select Special Device */
    #define LPA     0130000   /* Load Peripheral Address */
    #define LPR     0140000   /* Load Peripheral Register */
    #define LPD     0150000   /* Load Peripheral Data */
    #define RPD     0160000   /* ReadBack Peripheral Data */
    #define MEMRB     00400   /* SPD - Memory Read-Back */
    #define DATA      01000   /* SPD - Byte Unpacking */
    #define   ALPHA   06000   /* LPR - Alphanumeric data */
    #define   GRAPH   04000   /* LPR - Graphic data */
    #define   IMAGE   02000   /* LPR - Image data */
    #define   LTHENH  01000   /* take lo byte then hi byte */
    #define   DROPBYTE 0400   /* drop last byte */
    #define INTERR    02000   /* SPD - Interrupt Enable */
    #define TEST      04000   /* SPD - Diagnostic Test */
   The MOS driver is called grin.obj. It operates on  the  fol-
   lowing IORB entries.
   iruva
        This is a pointer to  the  buffer  where  the  data  is
        stored.

GRINNELL(DEV) GRINNELL(DEV)

        This data must be ready formtatted  for  the  Grinnell,
        since no conversion is performed by the driver.
   irbr
        This transfer length as a positive number of bytes.
   Addressing the grinnell. Rows consist of elments numbered  0
   to 511 running left to right. The lines are number from 0 to
   511 running from bottom to top. It is thus  addressed  as  a
   conventional  X-Y  coordinate system. Note that this coordi-
 e system is different the one used for the image.
      X A
        |
        |                                 (511, 511)
    511 +-------------------------------+
        |                               |
        |                               |
        |                               |
        |                               |
        |             (x, y)            |
        |            +                  |
        |                               |
        |                               |
        |                               |
        |                               |
        |                               |
        +-------------------------------+----->
       0                               511    Y

SEE ALSO

   grinnell(fax)

DACOM(DEV) DACOM(DEV)

NAME

   dacom - facsimile machine

SYNOPSIS

   DCT faxinput
   setdct("faxin", 0350, 0174750, 0174740,
           faxii, faxin, faxini, &faxoutput);
   DCT faxoutput
   setdct("faxout", 0354, 0174752, 0174742,
           faxoi, faxot, faxoti, &faxinput);

DESCRIPTION

   The DACOM facsimile machine can read  a  document,  creating
   the  corresponding image data blocks. It can also accept the
   data of relevant format, printing the correponding image.
   Each data block consists of 585 bits, and  is  stored  in  a
   block  of  74 bytes starting on a byte boundary. The final 7
   bits of the last byte are not used and they  are  undefined.
   The  585 bits in each block need to be read as a bit stream:
   the bits in each byte run from the high  orger  end  of  the
   byte  to the low order end. The last 12 bits of the 585 bits
   in each block consistute the CRC field whereby the block can
   be validated.
   There are two kinds of blocks: SETUP blocks and DATA blocks.
   The  first of block of an image data file should be a single
   SETUP block. All following blocks in the file must  be  DATA
   blocks. Note that the second block is a DATA block that con-
   tains ZERO samples, i.e. a dummy data blocks. Form the third
   block, the DATA blocks store the reall image data.
   A standard dacom page contains about 1200 scan  lines,  each
   of which has 1726 pels. One can choose

UCL FACSIMILE SYSTEM INDRA Note 1185

        Appendix II: Task Controller and Task Processes

CCITT(FAX) CCITT(FAX)

NAME

   ccitt - conversion between vector and CCITT T4 format

SYNOPSIS

   ccitt() - a MOS task
   command string (task name is defined as ccitt):
   ccitt"<function>

DESCRIPTION

   This routine operates as a MOS pipe task to convert the vec-
   tors to CCITT T4 format or inversely.
   The parameter function specifies what the task is to do.
    value           function
     1c             one-dimensional compression
     1d             one-dimensional decompression
     2c[<k>]        two-dimensional compression
     2d             two-dimensional decompression
   Note k is the maximun number  of  lines  to  be  coded  two-
   dimensionally  before  a one-dimensionally coded line is in-
   serted. If k is omitted, the default value 2 is adopted.

SEE ALSO

   vector(fax), t4(fax), fitter(fax)

CHECK(FAX) CHECK(FAX)

NAME

   check - check the validity of a vector file.

SYNOPSIS

   check() - a MOS task
   command string (the task name is defined as check):
   check"<function>,<width>,<height>,[<from>,<to>]

DESCRIPTION

   This routine operates as a MOS pipe task checking the  vali-
   dity of the input vector file.
   The number of lines to be checked is specified by the param-
   eter  height.   If  the height of the image is less than the
   parameter, the actual height is printed. Thus, one  can  set
   the  parameter  height to a big number in order to count the
   number of lines of the input image.
   The run lengths in each of these lines are  accumulated  and
   the sum is compared with the parameter width.
   These are the basic functions which are  performed  whenever
   the  task is invoked. However, there are several options one
   can choose by setting the one-character parameter function.
    value         function
     'n'          basic function only
     'c'          print the count of each line
     'l'          print all lines
     's'          print the lines in the interval
                  specified by parameter from and to

DIAGNOSTICS

   A bad line will be reported and it will cause the job abort-
   ed.

SEE ALSO

   vector(fax), getl(fax), fitter(fax)

CHOP(FAX) CHOP(FAX)

NAME

   chop - extract a designated rectangular area from an image

SYNOPSIS

   chop() - a MOS task
   command string (task name is defined as chop):
   chop"<x0>,<y0>,<x1>,<y1>

DESCRIPTION

   This routine operates as a MOS pipe task extracting a desig-
   nated  rectangular area from an input image.  Input and out-
   put are image data files in the form of vectors.
   The following diagram  shows  the  coordinate  system  being
   used.  Note that the lengths are measured in number of pels.
        (0, 0)                     width  X
           +-------------------------+---->
           |                         |
           |                         |
           |   (x0, y0)              |
           |     +---------+         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     +---------+         |
           |            (x1, y1)     |
           |                         |
           |                         |
           |                         |
           |                         |
    height +-------------------------+
           |
           |
         Y V
   As can be seen in the diagram, the rectangular  area  to  be
   extracted  is  specified  by  the parameters x0, x1, y0, y1,
   which are decimal strings.

BUGS

   One has to make sure that

CHOP(FAX) CHOP(FAX)

           0 < x0 < width
           0 < y0 < height
           0 < x1 < width
           0 < y1 < height

SEE ALSO

   vector(fax), getl(fax), putl(fax), fitter(fax)

CLEAN(FAX) CLEAN(FAX)

NAME

   clean - clean an image.

SYNOPSIS

   clean() - a MOS task
   command string (task name is defined as clean):
   clean"<width>,<height>

DESCRIPTION

   This routine operates as a MOS pipe task cleaning  an  image
   by  means of mask scanning.  Input and output are image data
   files in the form of vectors.
   The width and height should be given as the parameters.

SEE ALSO

   vector(fax), getl(fax), putl(fax), fitter(fax)

DECOMP(FAX) DECOMP(FAX)

NAME

   decomp - decompress DACOM blocks

SYNOPSIS

   decomp() - a MOS task
   command string (task name is defined as decomp):
   decomp

DESCRIPTION

   This task takes DACOM blocks from the Clean and  Simple  in-
   terface,  and  decompresses them into vector format. Then it
   writes the vectors to the Clean and Simple interface.

SEE ALSO

   dacom(dev), vector(fax), fitter(fax)

FAX(FAX) FAX(FAX)

NAME

   fax - interface process for DACOM facsimile machine

SYNOPSIS

   fax() - a MOS task
   command string (task name is defined as fax):
   fax"<function>

DESCRIPTION

   This task uses the Clean and Simple  interface  to  read  or
   write facsimile image data.
   The one character parameter function specifies  whether  the
   data  is  to be read or written. Character w is for writing.
   In this case, 74 byte DACOM  blocks  contaning  correct  CRC
   fields  are  expected. On the other hand, character r is for
   reading. In this case, a document is read on  the  facsimile
   machine, the DACOM blocks being created.

SEE ALSO

   dacom(dev), fitter(fax)

FITTER(FAX) FITTER(FAX)

NAME

   fitter - fit processes together to form a data pipe

SYNOPSIS

   fitter() - the MOS task controller

DESCRIPTION

   According to the command string typed on the console, fitter
   links the specified processes together to form a task chain.
   The name of the processes is the name given in the PCB.  The
   processes must communicate using the C+S interface. Only one
   C+S interface is opened per process - data is pushed in with
   a cswrite and pulled out with a csread.  The fitter does not
   inspect the data in any way but merely passes  it  from  one
   process to another.
   The format of command string is:
           A | B | C.
   The fitter takes data from the process called A, write it to
   the  process  called  B,  reads  data from the process B and
   write that data to the process  C.   Note  that  all  middle
   processes  are both read and written, while the first one in
   the list is only read from and the last in the list is  only
   written to.
   A double quote is used as the  separator  between  the  task
   name and the open parameter string, e.g.
           A"500 | B"n,xyz | C,
   where the strings '500' and 'n,xyz' are the  open  parameter
   stings  for  tasks  A  and  B,  respectively.  The parameter
   stirng is passed to the corresponding task routine when  the
   csopen call returns.

DIAGNOSTICS

   The command string containing undefined task will be reject-
   ed.

SEE ALSO

   csinit(fax), csopen(fax), csread(fax), cswrite(fax)

FS(FAX) FS(FAX)

NAME

   fs - file system for use under MOS

SYNOPSIS

   fs() - a MOS task
   command string (task name is defined as fs):
   fs"<funciton>,<file_name>

DESCRIPTION

   This is a file system, based on the  Double  Density  floppy
   disk,  for use under MOS. The fs task is used for manipulate
   the files, managed by the file system. This  task  can  only
   appear at the first or last position on a command string. In
   the former case, the file specified is to be read, while the
   file is to be written in the latter case.
   The <function> field contains only one character  indicating
   the function to be performed. The possible values are:
           e - open an existing file (for reading).
           c - open an existing file, and set the length
                     to zero (for rewriting).
           a - append to an existing file.
   If the capitals A, C, and E are used, the functions are  the
   same as described above but the specified file is created if
   it does not exist.

BUGS

   This task is for reading and writing only. As for the  other
   facilities,  e.g.  seek, delete, status and sync, one has to
   use C+S interface directly.
   Note that only 15 files are permitted per disk, only drive 0
   is  supported  at  present, and no hierarchical directory is
   allowed.

SEE ALSO

   aed62(dev), fitter(fax)

FTP(FAX) FTP(FAX)

NAME

   ftp, pftp - NIFTP task processes

SYNOPSIS

   ftp(), pftp() - MOS tasks
   command string (task name is defined as ftp):
   ftp"<function>,<code>,<user_name>,<password>,<file_name>;
       <trasport_service_process>:<transport_service_parameters>

DESCRIPTION

   These tasks are implementation of Network  Independent  File
   Transfer  Protocol (NIFTP) for LSIs under MOS. They employ a
   transport service for communication with a  remote  host  on
   the network, where the same protocol must be supported. They
   communicate with the  user  process  and  transport  service
   processes  thourgh  the  Clean and Simple interface, so that
   they can be used in a fitter command chain directly.
   The code is available in two versions: ftp which  is  a  P+Q
   version supporting both server and intitiator and pftp which
   is a P version working only as an initiator.  Both  of  them
   are capable of sending and receiving.
   This implementation of NIFTP is just a subset of the  proto-
   col  as its main purpose is to provided the facsimile system
   with a data transmission mechanism. For the sake of  simpli-
   city,  only  the  necessary  facilities  are included in the
   module, while more complex facilities, such as data compres-
   sion  and  error recovery are not implemented. The following
   table shows the transfer control parameters being used.
    Attribute       Value Mod. Remarks
    Mode of access  0001  EQ   Creating a new file
                    8002  EQ   Retrieving file
    Codes            -    -    Text file, any parity
                    1002  EQ   Binary file
    Format effector 0000  EQ   No interpretation
    Binary mapping  0008  EQ   Default byte size
    Max record size 00FC  EQ   Default record size
    Transfer size   0400  LE   Default transfer size
    Facilities      0000  EQ   Minimum service
   The meanings of the parameters in  the  command  string  are
   listed below:
   function is the NIFTP function of our site. Any ASCII string
   beginning

FTP(FAX) FTP(FAX)

   beginning with 't' means the file is to  be  transmitted  to
   the remote site.  Otherwise, the file will be retrieved from
   the remote site.
   code specifies the type of the file to be  transferred.  Any
   ASCII  string  beginning with 'b' means it is a binary file,
   while others mean text file.
   user_name is the login name of the server site.
   password is the password of the server site.
   file_name is the name of the file to be transmitted.
   transport_service_process is the process name of  the  tran-
   sport service to be used.
   transport_service_parameters are the  parameter  string  re-
   quired by the transport service.  They are network dependent
   and specified by the corresponding transport service.

SEE ALSO

   fitter(fax)

GRINNELL(FAX) GRINNELL(FAX)

NAME

   grinnell - task to convert and display fax vector data

SYNOPSIS

   grinnell() - a MOS task
   command string (task name is defined as string):
   grinnell"<x0>,<y0>,<x1>,<y1>,<mode>,<colour>

DESCRIPTION

   This task takes the vector data from a Clean and Simple  in-
   terface and displays it on the Grinnell screen. The Grinnell
   screen is viewed as an X-Y plane with (0,0) being the  lower
   left  hand  corner,  (512,  0)  being  the  lower right hand
   corner, etc.
   The parameters x0, y0, x1, y1 are decimal  strings  defining
   the rectangular space on the screen where the image is to be
   displayed. If the image is smaller than this area, it is ar-
   tificially  expanded  to the size of this area. If the image
   is larger than this area it is truncated to the size of  the
   area.
   The colour field consists of any combination of the  charac-
   ters  r,g  or  b  to  define the colours red, green and blue
   respectively. For instance "gb" would  write  the  image  as
   yellow.
   The mode defines how the image is to be displayed. Any  com-
   bination  of  the  characters  r,a and z may be used, to the
   following effect:
           r = reverse image
           a = additive image
           z = zerowrite image.
   There are three bit planes to define the three colours. Nor-
   mally  the  bit planes corresponding to the selected colours
   have either zero bits or one bits written to them  depending
   upon  whether  the image or the background is being written.
   For zerowrite, all non-selected bit planes  (i.e.   colours)
   are  always set to zero, thus erasing any unselected colours
   in the area. Additive mode means that in the selected colour
   planes  the  new bits are ORed in, rather than just written.
   Thus the image is added to. In reverse mode, the image writ-
   ten as one bits is written as zero bits and the bits written
   as zero bits are written as one  bits,  i.e.  the  bits  are
   flipped before being used.

GRINNELL(FAX) GRINNELL(FAX)

SEE ALSO

   grinnell(dev), vector(fax), fitter(fax)

MERGE(FAX) MERGE(FAX)

NAME

   merge - merge two images together

SYNOPSIS

   merge() - a MOS task
   command string (task name is defined as merge):
   merge"<file_name>,<action>,<x0>,<y0>,<x1>,<y1>

DESCRIPTION

   This routine operates as a MOS pipe task merging two  images
   together to form the result image.  Input and output are im-
   age data files in the form of vectors.
   One of the two input images is called background which is to
   be  copied  directly.  This  is  specified  by the parameter
   file_name.  The image data of the back ground is read via  a
   'tunnel',  maintained  by  this task. Another input image is
   taken form the Clean and Simple  interface  managed  by  the
   fitter.   As  shown  in  the following diagram, the position
   where it is to be put on the background image  is  specified
   by the parameters x0, y0, x1, y1, which are decimal strings.
   This implies that the dimension of the image is x1 - x0  and
   y1 -y0.
        (0, 0)                     width  X
           +-------------------------+---->
           |                         |
           |   (x0, y0)              |
           |     +---------+         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     |         |         |
           |     +---------+         |
           |            (x1, y1)     |
           |                         |
           |                         |
           |       (back ground)     |
    height +-------------------------+
           |
           |
         Y V
   The parameter  action  indicates  how  the  two  images  are
   merged.  If it set to 0, The second image is simply overlaid
   on the back ground image. On the  other  hand  any  non-zero
   value

MERGE(FAX) MERGE(FAX)

   causes the second image to replace the specified area of the
   back ground image.

BUGS

   One has to make sure that
           0 < x0 < width_of_back_ground
           0 < y0 < height_of_back_ground
           0 < x1 < width_of_back_ground
           0 < y1 < height_of_back_ground
   In addition, x0, y0, x1, y1 must be consistent with the  di-
   mension of the image

SEE ALSO

   vector(fax), getl(fax), putl(fax), chop(fax), fitter(fax)

OD(FAX) OD(FAX)

NAME

   od - dump the input data

SYNOPSIS

   od() - a MOS task
   command string (task name is defined as od):
   od"<format>

DESCRIPTION

   This routine operates as a MOS pipe task dumping  the  input
   data in a selected format.  The input data is taken from the
   Clean and Simple interface.
   The meanings of the one character parameter format are:
          value          format
           'd'           words in decimal
           'o'           words in octal
           'c'           bytes in ASCII
           'b'           bytes in octal

SEE ALSO

   fitter(fax)

RECOMP(FAX) RECOMP(FAX)

NAME

   recomp - compress the vectors to form the DACOM blocks

SYNOPSIS

   recomp() - a MOS task
   command string (task name is defined as recomp):
   recomp

DESCRIPTION

   This task takes vectors from the Clean and Simple interface,
   and  recompresses them into DACOM blocks. Then it writes the
   blocks to the Clean and Simple interface.

SEE ALSO

   dacom(dev), vector(fax), fitter(fax)

SCALE(FAX) SCALE(FAX)

NAME

   scale - scale an image to a specified dimension

SYNOPSIS

   scale() - a MOS task
   command string (task name is defined as scale):
   scale"<old_width>,<old_height>,<new_width>,<new_height>

DESCRIPTION

   This routine operates as a MOS pipe task scaling  the  input
   image  to the specified dimension.  Input and output are im-
   age data files in the form of vectors.
   The dimension of the input image is given by the  parameters
   old_width  and old_height, while the dimension of the output
   is specified by the parameters new_width and new_height.

SEE ALSO

   vector(fax), getl(fax), putl(fax), fitter(fax)

STRING(FAX) STRING(FAX)

NAME

   string - convert an ASCII string to the vector format

SYNOPSIS

   string() - a MOS task
   command string (task name is defined as string):
   string"<s>

DESCRIPTION

   This routine operates as a  MOS  pipe  task  converting  the
   parameter string s to the corresponding vectors.

SEE ALSO

   vector(fax), ts(fax)

TF(FAX) TF(FAX)

NAME

   tf - convert a text to the vector format.

SYNOPSIS

   tf() - a MOS task
   command string (task name is defined as tf):
   tf"<width>,<line_sp>,<upper>,<left>

DESCRIPTION

   This routine operates as a MOS pipe task converting the  in-
   put text to the corresponding vectors. The input text, taken
   from the Clean and Simple interface should be in the  format
   defined in text(fax).
           +-------------------------+
           |                         |
           |            upper        |
           |                         |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |  left   XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |         XXXXXXXXXXXX    |
           |            width        |
           |                         |
           +-------------------------+
   As shown in the diagram, the parameters give the information
   for  the formating. The parameter width is the maximum width
   of the text lines.
   Every vector will be padded to fit this  width.  White  pels
   may be padded to the left of each vectors, and the number of
   pel to be padded is specified by the parameter left.
   Empty lines may also be inserted. They are defined by param-
   eters  upper  and  line_sp, the number of pels being used as
   the unit.

SEE ALSO

   vector(fax), text(fax), ts(fax), fitter(fax)

UCL FACSIMILE SYSTEM INDRA Note 1185

        Appendix III: Utility Routines and Data Formats

BITMAP(FAX) BITMAP(FAX)

NAME

   bitmap - convert vector format to core bit map

SYNOPSIS

   int  bitmap(ivec, cnt, buff);
   int  *ivec;
   int  cnt;
   char *buff;

DESCRIPTION

   Bitmap converts the fax vector format into a bit map,  using
   each bit of the area pointed to by buff.  The number of ele-
   ments in ivec is given by cnt, and the first element of ivec
   is  taken  as  a  white pel count, the second as a black pel
   count, etc. The resultant bit map  is  placed  in  the  area
   pointed  to by buff. The actual number of bits stored is re-
   turned from the function.  The bits in buff  are  stored  in
   byte  order, with the highest value bit of the byte taken as
   the first bit of the byte.

BUGS

   You have to make sure that buff is big enough  for  all  the
   bits.

SEE ALSO

   vector(fax), tovec(fax)

TOVEC(FAX) TOVEC(FAX)

NAME

   tovec - convert bitmap to vector format

SYNOPSIS

   int  *tovec(buff, nbits);
   char *buff;
   int  nbits;

DESCRIPTION

   The bitmap in the buffer pointed to by buff is converted  to
   vector format. The length of the bitmap in bits is passed in
   nbits.  As the caller would normally not know how many  vec-
   tor elements are going to be needed, the tovec routine allo-
   cates this area for the user.
   Buff is assumed to be  organised  in  byte  order  with  the
   highest  value  bit  of each byte being the first bit of the
   byte. The counts of white and black pels are placed into  an
   integer  vector, the first element of which is the length of
   the rest of the vector. The vector information proper starts
   in  the  second  element which is the count of the number of
   leading white pels.  This is followed by the  count  of  the
   numbr of black pels, etc.
   The routine goes to great lengths to make sure  only  enough
   vector  storage is allocated. Temporary storage is allocated
   in small chunks and then, when the length of the whole  vec-
   tor  is known, the chunks are contacenated into a contiguous
   vector.  The pointer to this vector is returned to the user.

SEE ALSO

   vector(fax), bitmap(fax)

CHOICE(FAX) CHOICE(FAX)

NAME

   choice - specify a rectangular area on Grinnell

SYNOPSIS

   struct  square  {
           int  x0, y0;
           int  x1, y1;
   };
   struct  square  *choice(colour, height, width, area, fw, fh)
   char colour;
   int  height, width, area, fw, fh;

DESCRIPTION

   This subroutine is called by a MOS task.  to specify a  rec-
   tangular  area  of  an image by manipulating a square on the
   Grinnel display being illustrating the image. The  dimension
   of  the  original image is defined as height and width.  The
   area on which the original image is shown  is  specified  by
   the parameter area.
    value       area           dimension    coordinates
      0     the whole screen    512x512     0,511,511,0
      1     the left half       256x512     0,511,255,0
      2     the right half      256x512     256,511,511,0
   The square will be drwan in a colour defined by the  parame-
   ter colour, which can only be:
           value   colour
            'r'     red
            'g'     green
            'b'     blue
   There are two modes being supported:
    (1) Fixed: The square will have a fixed dimension specified
        by the parameters fw and fh.  The operator can move the
        square around as a whole within the predetermined  area
        by  using  following commands, each of which is invoked
        by typing the corresponding characer on the keyboard of
        the system console.

CHOICE(FAX) CHOICE(FAX)

         command         function
           'u'           move the square up one step
           'd'           move the square down one step
           'l'           move the square one step left
           'r'           move the square one step right
           'f'           move fast - set the step to 8 pel
           'o'           move slowly - set the step to 1 pel
           <CR>          ok - the area has been chosen, and
                        return its coordinates
    (2) Arbitrary: This mode is set up when the  subroutine  is
        called  with  the  parameters  fw and fh set to 0.  Any
        edge of the square can be selected to be moved  on  its
        own  by  using  the  same commands described above. The
        following commands are required to select the  relevant
        edge as well as switching the operation mode.
         command         function
           'e'           select the right ('east') edge.
           'w'           select the left ('west') edge.
           'n'           select the upper ('north') edge.
           's'           select the lower ('south') edge.
           'a'           move the square as a whole
   As soon as the user  types  <CR>,  the  coordinates  of  the
   current  square,  which  are accommodated in a square struc-
   ture, are returned. Note these are concerned with the  coor-
   dinate  system  defined  for the image but not for the grin-
   nell.

BUGS

   Currently, only three working areas can be used.

SEE ALSO

   vector(fax), grinnell(dev), grinnell(fax)

CRC(FAX) CRC(FAX)

NAME

   crc - calculate or check the DACOM CRC code

SYNOPSIS

   int  crc(buff, insert);
   char *buff;
   int  insert;

DESCRIPTION

   This routine will check/insert the 12-bit  CRC  code  for  a
   DACOM  block,  pointed  to  by buff.  The block contains 585
   bits, the last 12 bits being the  CRC  code.  The  block  is
   checked  only  when the parameter insert is set to 0, other-
   wise the CRC code is created and inserted  into  the  block.
   When the block is checked, the routine returns the result: 0
   means OK and any non-zero value means the block is  bad.  On
   the  other  hand, when the CRC code is inserted, the routine
   returns the CRC code it has created.
   This routine uses a tabular approach to  determine  the  CRC
   code,  processing  a whole byte at a time and resulting in a
   high throughput.

BUGS

   Do not forget to supply enough space  when  the  12-bit  CRC
   code is to be inserted.

SEE ALSO

   dacom(dev)

CSINIT(FAX) CSINIT(FAX)

NAME

   csinit - initiate the Clean and Simple interface

SYNOPSIS

   int  csinit();

DESCRIPTION

   This routine is called to initiate the Clean and Simple  in-
   terface for the calling process.  Its code is re-entrant, so
   that only one copy is needed for all processes in a system.
   This routine returns the task identifier, which must be used
   on all subsequent interface calls.

SEE ALSO

   csopen(fax), csread(fax), cswrite(fax), fitter(fax)

CSOPEN(FAX) CSOPEN(FAX)

NAME

   csopen - establish the Clean and Simple connection

SYNOPSIS

   char *csopen(tid);
   int  tid;

DESCRIPTION

   A process calls this routine, waiting to be scheduled.   Its
   code  is re-entrant, so that only one copy is needed for all
   processes in a system.
   The task identifier tid is the word returned from the csinit
   call.  When the fitter process has established the Clean and
   Simple connection for the process, this routine returns  the
   pointer  to  the  parameter string of the corresponding task
   command.

SEE ALSO

   csinit(fax), csread(fax), cswrite(fax), fitter(fax)

CSREAD(FAX) CSREAD(FAX)

NAME

   csread - read data from the Clean and Simple interface

SYNOPSIS

   char *csread(tid, need);
   int  tid, need;

DESCRIPTION

   This routine is called to read data from the Clean and  Sim-
   ple interface. Its code is re-entrant, so that only one copy
   is needed for all processes in a system.
   The task identifier tid is the word returned from the csinit
   call.  The need parameter indicates the number of bytes that
   are required. This routine returns a  pointer  to  a  buffer
   with this much data in it. This is usually more efficient as
   it means that the data does not have to be reblocked.

DIAGNOSTICS

   If the returned value is 0, the end of data is reached.

BUGS

   Funnies happen at the end of data to be read.  The  csread()
   call  has  no  way of saying that the final buffer is partly
   filled.  Thus if you ask for more data,  you  hang  forever.
   But  if  the  data  structures  are  working correctly, this
   should never happen.

SEE ALSO

   csinit(fax), cswrite(fax), fitter(fax)

CSWRITE(FAX) CSWRITE(FAX)

NAME

   cswrite - write data to the Clean and Simple interface

SYNOPSIS

   char *cswrite(tid, need);
   int  tid, need;

DESCRIPTION

   This routine is call to write data to the Clean  and  Simple
   interface.  Its code is re-entrant, so that only one copy is
   needed for all processes in a system.
   The task identifier tid is the word returned from the csinit
   call.  The need parameter indicates the number of bytes that
   are to be written. This routine returns a  write  buffer  of
   the  required  length, to which the user data can be copied.
   The subsequent cswrite()  call  automatically  releases  the
   previous write buffer.
   The cswrite() call with need set to 0 indicates the  end  of
   data, closing the current Clean and Simple connection.

BUGS

   As indicated, the write buffer must be filled up before  the
   next cswrite() call.

SEE ALSO

   csinit(fax), csread(fax), fitter(fax)

GETL(FAX) GETL(FAX)

NAME

   getl - get a line vector from the Clean and Simple interface

SYNOPSIS

   int  *getl(tid);
   int  tid, need;

DESCRIPTION

   This routine is called to read a line vector from the  Clean
   and  Simple  interface. Its code is re-entrant, so that only
   one copy is needed for all processes in a system.
   The task identifier tid is the word returned from the csinit
   call.  The  routine  returns the pointer to the buffer where
   the line vector is stored.

DIAGNOSTICS

   0 will be returned when end of file is reached.

BUGS

   Any memory violation causes  the  whole  task  chain  to  be
   aborted.

SEE ALSO

   vector(fax), putl(fax), fitter(fax)

PUTL(FAX) PUTL(FAX)

NAME

   putl - put a line vector to the Clean and Simple Interface

SYNOPSIS

   putl(tid, buf);
   int  tid, *buf;

DESCRIPTION

   This routine is called to write a line vector to  the  Clean
   and  Simple  interface. Its code is re-entrant, so that only
   one copy is needed for all processes in a system.
   The task identifier tid is the word returned from the csinit
   call. The line vector is stored in a buffer pointed by buf.

SEE ALSO

   vector(fax), getl(fax), fitter(fax)

T4(FAX) T4(FAX)

NAME

   t4 - the data format defined in CCITT recommendation T4

DESCRIPTION

   Dimension and Resolution: In vertical direction the  resolu-
   tion is defined below.
           Standard resolution:            3.85 line/mm
           Optional higher resolution:     7.70 line/mm
   In horizontal direction, the standard resolution is  defined
   as  1728 black and white picture elements along the standard
   line length of 215 mm.  Optionally, there  can  be  2048  or
   2432 picture elements along a scan line length of 255 or 303
   mm, respectively. The input documents up to a minimum of ISO
   A4 size should be accepted.
   One-Dimensional Coding: The one-dimensional run length  data
   compression  is accomplished by the popular modified Huffman
   coding scheme. In this scheme, black and white runs are  re-
   placed  by  a  base  64 codes representation. Compression is
   achieved since the code word lengths are invertly related to
   the  probability  of  the  occurrence of a particular run. A
   special code (000000000001), known as  EOL  (End  of  Line),
   follows  each  line  of data. This code starts the facsimile
   message phase, while the control phase is restored by a com-
   bination  of six contiguous EOLs (RTC). The data format of a
   facsimile message is shown below.
    start of the facsimile data
    |
    v
    +---+------+---+------+-/
    !EOL! DATA !EOL! DATA !
    +---+------+---+------+-/
                  end of the facsimile data
                                          |
                                          v
     /-+---+------+---+---+---+---+---+---+
       !EOL! DATA !EOL!EOL!EOL!EOL!EOL!EOL!
     /-+---+------+---+---+---+---+---+---+
                  |<------   RTC  ------->|
   Two-Dimensional Coding: The two-dimensional coding scheme is
   labeled  as  the  Modified READ Code. It codes one line with
   reference to the line above,correlation  between  adja-
   cent lines allowing for more efficient compression. In order
   to limit the disturbed area in the event of transmission er-
   rors,

T4(FAX) T4(FAX)

   a one-dimensionally coded line is transmitted after  one  or
   more  two-dimensionally  coded  lines.  A bit, following the
   EOL, indicates whether one-  or  two-dimensional  coding  is
   used for the next line:
           EOL1: one-dimensional coding;
           EOL0: two-dimensional coding.
    start of the facsimile data
    |
    v
    +----+--------+----+--------+-/
    !EOL1!DATA(1D)!EOL0!DATA(2D)!
    +----+--------+----+--------+-/
                           end of the facsimile data
                                                   |
                                                   v
     /-+----+--------+----+----+----+----+----+----+
       !EOL0!DATA(2D)!EOL1!EOL1!EOL1!EOL1!EOL1!EOL1!
     /-+----+--------+----+----+----+----+----+----+
                     |<---------   RTC   --------->|

TEXT(FAX) TEXT(FAX)

NAME

   text - the text format for use in the facsimile system

DESCRIPTION

   This is the representation  structure  for  coded  character
   text.  It is used in the facsimile system.
   The  text  structure  consists  of  a  series  of  character
   strings,  each  of  which represents a text line. However no
   control characters, e.g. <CR> and  <LF>,  are  used  in  the
   structure. Each text line is proeeded by a count byte, indi-
   cating the number of characters on the line.  The  character
   sting  follows  after the the count byte. A zero count indi-
   cates the end of file.

EXAMPLES

   Here is an example text shown below:
           This is a text.
           This is a picture.
   It can be represented as:
    <017> T  h  i  s <040> i  s <040> a <040> t  e  x  t  .
    <022> T  h  i  s <040> i  s <040> a <040> p  i  c  t  u
    r e  . <0>

TS(FAX) TS(FAX)

NAME

   ts - translate an ASCII string into vector format

SYNOPSIS

   ts(ar_in, left, right, tid)
   char *ar_in;
   int  left, right, tid;

DESCRIPTION

   This routine will convert a zero-ended ASCII string  pointed
   to  by  ar_in  into  the corresponding vecter format. As the
   character font being used is a set of 12x20 matrices,  there
   will  be  20 line vectors created. These vectors are written
   to the Cleans and Simple interface by calling cswrite.   The
   callers task identifier tid has to be provided.
   At the two ends of the text line, blanks can be padded  that
   are  specified  as left and right.  Note that they are meas-
   ured in pels.
   Consequently, the result should be a image, whose  dimension
   is:
           width  = left + 12*length + right;
           height = 20;
   where length is  the  number  of  characters  in  the  input
   string.
   As an intermediate result the bitmap is first created  which
   is then converted into the vector format, by calling tovec.

BUGS

   The input string must be ended with a zero field.

SEE ALSO

   vector(fax),    tovec(fax),    csinit(fax),    cswrite(fax),
   fitter(fax)

VECTOR(FAX) VECTOR(FAX)

NAME

   vector - the internal data structure for a facsimile image

DESCRIPTION

   This is the representation structure for  binary  images,  a
   simple  run length compression algorithm being used. Most of
   the image files are kept in vector format for ease  of  pro-
   cessing.
   The vector format consists of a series of  integer  vectors,
   one vector for each row of pels in the image. Each vector is
   proceeded by a count word which indicates the number of  in-
   teger  words  in the vector.  The next element of the vector
   after the count field is the number of  white  pels  in  the
   first  run  of  the  line.   The  second word then gives the
   number of pels that follow the initial white run, and so  on
   t  the  end of the vector. Note the first run length element
   must refer to a white run. It should be  set  to  0  if  the
   first run is black.

EXAMPLES

   A line consists of 20 pels as follows:
           00011111111011100000
   It can be represented as:
           5, 3, 8, 1, 3, 5
   The inverse of the line:
           11100000000100011111
   should be represented as:
           6, 0, 3, 8, 1, 3, 5
/data/webs/external/dokuwiki/data/pages/rfc/rfc809.txt · Last modified: 1991/10/17 17:55 by 127.0.0.1

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