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pbmtojbg(1)





NAME

       pbmtojbg - portable bitmap to JBIG1 file converter


SYNOPSIS

       pbmtojbg [ options ] [ input-file | -  [ output-file ]]


DESCRIPTION

       Reads  in  a  portable bitmap (PBM) from a file or standard input, com-
       presses it, and outputs the image as  a  JBIG1  bi-level  image  entity
       (BIE) file.

       JBIG1 is a highly effective lossless compression algorithm for bi-level
       images (one bit per pixel), which is particularly suitable for  scanned
       document pages.

       A JBIG1 encoded image can be stored in several resolutions (progressive
       mode).  These resolution layers can be stored all in one single BIE  or
       they  can be stored in several separate BIE files.  All resolution lay-
       ers except the lowest one are stored merely as differences to the  next
       lower  resolution layer, because this requires less space than encoding
       the full image completely every time. Each resolution layer  has  twice
       the number of horizontal and vertical pixels than the next lower layer.
       JBIG1 files can also store several bits per pixel  as  separate  bitmap
       planes, and pbmtojbg can read a PGM file and transform it into a multi-
       bitplane BIE.


OPTIONS

       -             A single hyphen instead of an input file name will  cause
                     pbmtojbg  to  read  the  data from standard input instead
                     from a file.

       -q            Encode the image in one single resolution layer  (sequen-
                     tial  mode).  This is usually the most efficient compres-
                     sion method. By default, the number of resolution  layers
                     is  chosen automatically such that the lowest layer image
                     is not larger than 640 x 480 pixels.

       -x number     Specify the maximal horizontal size of the lowest resolu-
                     tion layer.  The default is 640 pixels.

       -y number     Specify  the  maximal vertical size of the lowest resolu-
                     tion layer.  The default is 480 pixels.

       -l number     Select the lowest resolution layer that will  be  written
                     to  the  BIE. It is possible to store the various resolu-
                     tion layers of a JBIG1 image  in  progressive  mode  into
                     different  BIEs.  Options  -l  and -h allow to select the
                     resolution-layer interval that will appear in the created
                     BIE. The lowest resolution layer has number 0 and this is
                     also the default value. By default  all  layers  will  be
                     written.

       -h number     Select  the highest resolution layer that will be written
                     to the BIE. By default all layers will  be  written.  See
                     also option -l.

       -b            Use  binary values instead of Gray code words in order to
                     encode pixel values in multiple  bitplanes.  This  option
                     has only an effect if the input is a PGM file and if more
                     than one bitplane is produced. Note that the decoder  has
                     to  make the same selection but cannot determine from the
                     BIE, whether Gray or binary code words were used  by  the
                     encoder.

       -d number     Specify  the total number of differential resolution lay-
                     ers into which the input image will be split in  addition
                     to  the  lowest  layer. Each additional layer reduces the
                     size of layer 0 by 50 %. This option overrides options -x
                     and  -y  which  are  usually  a  more  comfortable way of
                     selecting the number of resolution layers.

       -s number     The JBIG1 algorithm splits each image into  a  number  of
                     horizontal  stripes.  This  option  specifies  that  each
                     stripe shall have number lines in layer  0.  The  default
                     value  is  selected so that approximately 35 stripes will
                     be used for the whole image.

       -m number     Select the maximum horizontal offset of the adaptive tem-
                     plate  pixel.   The JBIG1 encoder uses a number of neigh-
                     bour pixels in order to get statistical a  priori  knowl-
                     edge  of  the probability, whether the next pixel will be
                     black or white. One single pixel out of this template  of
                     context  neighbor  pixels can be moved around. Especially
                     for dithered images it can be a significant advantage  to
                     have one neighbor pixel which has a distance large enough
                     to cover the period of a dither function. By default, the
                     adaptive template pixel can be moved up to 8 pixels away.
                     This  encoder  supports  up  to  23  pixels,  however  as
                     decoders are only required to support at least a distance
                     of 16 pixels by the standard, no higher value than 16 for
                     number is recommended in order to maintain interoperabil-
                     ity with other JBIG1 implementations. The maximal  verti-
                     cal offset of the adaptive template pixel is always zero.

       -t number     Encode only the specified number of most significant  bit
                     planes.  This  option  allows  to  reduce the depth of an
                     input PGM file if not all bits per pixel  are  needed  in
                     the output.

       -o number     JBIG1 separates an image into several horizontal stripes,
                     resolution layers and planes, were  each  plane  contains
                     one  bit  per  pixel.  One single stripe in one plane and
                     layer is encoded as a data unit called stripe data entity
                     (SDE)  inside  the  BIE.  There are 12 different possible
                     orders in which the SDEs can be stored inside the BIE and
                     number  selects which one shall be used. The order of the
                     SDEs is only  relevant  for  applications  that  want  to
                     decode  a JBIG1 file which has not yet completely arrived
                     from e.g. a slow network connection.  For  instance  some
                     applications prefer that the outermost of the three loops
                     (stripes, layers, planes) is over all layers so that  all
                     data of the lowest resolution layer is transmitted first.
                     The  following  values  for  number  select  these   loop
                     arrangements for writing the SDEs (outermost loop first):

                        0      planes, layers, stripes
                        2      layers, planes, stripes
                        3      layers, stripes, planes
                        4      stripes, planes, layers
                        5      planes, stripes, layers
                        6      stripes, layers, planes

                     All loops count starting with zero, however by  adding  8
                     to  the  above order code, the layer loop can be reversed
                     so that it counts down to zero and then higher resolution
                     layers will be stored before lower layers.  Default order
                     is 3 which writes at first all planes of the first stripe
                     and  then  completes  layer  0 before continuing with the
                     next layer and so on.

       -p number     This option allows  to  activate  or  deactivate  various
                     optional  algorithms  defined in the JBIG1 standard. Just
                     add the numbers of the following options which  you  want
                     to activate in order to get the number value:

                        4      deterministic prediction (DPON)
                        8      layer 0 typical prediction (TPBON)
                       16      diff. layer typ. pred. (TPDON)
                       64      layer 0 two-line template (LRLTWO)

                     Except  for special applications (like communication with
                     JBIG1 subset implementations) and for debugging  purposes
                     you  will  normally not want to change anything here. The
                     default  is  28,  which  provides  the  best  compression
                     result.

       -c            Determine  the  adaptive  template pixel movement as sug-
                     gested in annex C of the standard. By  default  the  tem-
                     plate change takes place directly in the next line, which
                     is most effective. However, a few conformance test  exam-
                     ples in the standard require the adaptive template change
                     to be delayed until the first line of  the  next  stripe.
                     This  option selects this special behavior, which is nor-
                     mally not required except in order to pass  some  confor-
                     mance tests.

       -Y number     A  long  time  ago, there were fax machines that couldn't
                     even hold a single page in  memory.  They  had  to  start
                     transmitting  data  before  the  page was scanned in com-
                     pletely and the length  of  the  image  was  known.   The
                     authors  of  the standard added a rather ugly hack to the
                     otherwise beautiful JBIG1 format  to  support  this.  The
                     NEWLEN  marker  segment  can  override  the  image height
                     stated in the BIE  header  anywhere  later  in  the  data
                     stream.  Normally  pbmtojbg never generates NEWLEN marker
                     segments, as it knows the correct image  height  when  it
                     outputs  the  header.  This option is solely intended for
                     the purpose of generating test files with  NEWLEN  marker
                     segments.  It  can  be  used  to specify a higher initial
                     image height for use in the BIE header, and pbmtojbg will
                     then  add  a NEWLEN marker segment at the latest possible
                     opportunity to the data  stream  to  signal  the  correct
                     final height.

       -v            After  the  BIE has been created, a few technical details
                     of the created file will be listed (verbose mode).


BUGS

       Using standard input and standard output for binary data works only  on
       systems  where  there  is no difference between binary and text streams
       (e.g., Unix). On other systems (e.g., MS-DOS), using standard input  or
       standard  output  may  cause  control  characters  like  CR or LF to be
       inserted or deleted and this will damage the binary data.


STANDARDS

       This program implements the JBIG1 image coding algorithm  as  specified
       in ISO/IEC 11544:1993 and ITU-T T.82(1993).


AUTHOR

       The  pbmtojbg  program  is part of the JBIG-KIT package, which has been
       developed by Markus Kuhn.  The most recent  version  of  this  portable
       JBIG1     library     and     tools     set     is    available    from
       <http://www.cl.cam.ac.uk/~mgk25/jbigkit/>.


SEE ALSO

       pbm(5), pgm(5), jbgtopbm(1)

                                  2003-06-04                       PBMTOJBG(1)

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