Provided by: djvulibre-bin_3.5.28-2ubuntu0.24.04.1_amd64 bug

NAME

       c44 - DjVuPhoto encode.

SYNOPSIS

       c44 [options] inputfilename [outputfilename]

DESCRIPTION

       Produces a DjVuPhoto encoded image.  The input image file inputfilename can be either a portable gray-map
       (PGM)  or  a  portable pix-map (PPM).  Input images compressed with JPEG are also accepted. It is however
       suggested to only use high quality JPEG files (low compression ratio, large  size)  because  the  wavelet
       compression will increase the defects already present in highly compressed JPEG files.

       The  program  produces  a  DjVuPhoto  file  outputfilename.   If the output file name is not specified, a
       default file name will be generated by replacing the input file name suffix by suffix djvu.

       The main design objective for the DjVu wavelets consisted of allowing progressive  rendering  and  smooth
       scrolling  of  large  images with limited memory requirements.  Decoding functions process the compressed
       data and update a memory efficient representation of the wavelet coefficients.  Imaging function then can
       quickly render an arbitrary segment of the image using the available data.  Both process can  be  carried
       out  in  two  threads  of  execution.   This  design  plays  an  important  role  in the DjVu system.  We
       investigated various state-of-the-art wavelet compression schemes.  Although these  schemes  may  achieve
       slightly  smaller  file  sizes,  the decoding functions did not even approach our requirements.  The IW44
       wavelets reach these requirements today and may in the future implement more modern refinements if  these
       refinements can be implemented within our constraints.

QUALITY SELECTION OPTIONS

       DjVuPhoto files are logically composed of a sequence of "slices" containing successive image refinements.
       Slices  are  grouped  in  "chunks"  defining  the  progressive rendering sequence.  The viewer is able to
       display an intermediate image after processing each chunk.  A typical DjVuPhoto files contains 80 to  120
       slices grouped into 1 to 4 chunks.

       The  quality  selection  options  provide  various ways to specify the number of chunks and the number of
       slices per chunk.  The c44 program adds slices to the current chunk until exceeding a  target  number  of
       slices,  a target file size, or a target quality specification.  The following options define targets for
       each chunk.  The option argument contain several numerical values (one per  chunk)  separated  by  either
       commas or pluses.

       -slice n+...+n
              Specify the number of slices in each chunk.  The option argument contains plus-separated numerical
              values  (one  per  chunk)  indicating the number of slices per chunk.  Option -slice 74+13+10, for
              instance, would be appropriate  for  compressing  a  photographic  image  with  three  progressive
              refinements.  More quality and more refinements can be obtained with option -slice 72+11+10+10.

       -slice n,...,n
              Specify  the cumulative number of slices for each chunk.  Since the final quality is determined by
              the total number of slices, it is often more convenient to use  comma-separated  values  (one  per
              chunk)  indicating the cumulative number of slices for each chunk (i.e. including those encoded in
              all previous chunks).  The values suggested above can also be expressed  as  -slice  74,87,97  and
              -slice 72,83,93,103.

       -size n,...,n
              Specify size targets for each chunk expressed in bytes.  The option argument can be either a plus-
              separated  list  specifying a size for each chunk, or a comma separated list specifying cumulative
              sizes for each chunk and all previous chunks.  Size targets  are  approximates.   Slices  will  be
              added to each chunk until exceeding the specified target.

       -bpp n,...,n
              Specify  size  targets for each chunk expressed in bits-per-pixel.  Both comma-separated and plus-
              separated specifications are accepted.  Option -bpp 0.25,0.5,1 usually provides good results.

       -percent n,...,n
              Specify size targets for each chunk expressed as a percentage of the input file size.  Both comma-
              separated and plus-separated specifications are accepted.  Results can  be  drastically  different
              according to the format of the input image (raw or JPEG compressed).

       -decibel n,...,n
              Specify  quality  targets for each chunk expressed as a comma-separated list of increasing decibel
              values.  Decibel values range from 16  (very  low  quality)  to  48  (very  high  quality).   This
              criterion  should  not  be  relied upon when re-encoding an image previously compressed by another
              compression scheme.  Selecting this option significantly increases the compression time.

       -dbfrac frac
              Indicate that the decibel values specified in option -decibel should be computed by averaging  the
              mean  squared  errors  of  only  the  fraction  frac of the most mis-represented blocks of 32 x 32
              pixels.  This option is useful with composite images containing  solid  color  features  (e.g.  an
              image with a large white border).

       Providing  no  quality specification options automatically selects a default quality specification -slice
       74,89,99.  Multiple quality specification options are allowed.  The program outputs a  file  whose  total
       number of chunks is the largest number of chunks of all quality specifications.  Slices are added to each
       chunk until reaching any of the quality target for this chunk.

OTHER OPTIONS

       The following additional options are supported:

       -dpi n Specify  the  resolution  information encoded into the output file expressed in dots per inch. The
              resolution information encoded in DjVu files determine how the  decoder  scales  the  image  on  a
              particular  display.   Meaningful  resolutions range from 25 to 1200.  The default value, 100 dpi,
              should be suitable for most photographic images.

       -gamma n
              Specify the gamma correction information encoded into the output file.  The argument  n  specified
              the  gamma  value  of the device for which the input image was designed. The default value is 2.2.
              This is appropriate for images designed for a standard computer monitor.

       -mask pbmfilename
              The design of the IW44 wavelets allows for compressing partially masked images.  This  option  can
              be  used  when  certain pixels of a background image are going to be covered by foreground objects
              like text or drawings.  File pbmfile must be a PBM file whose size matches the size of  the  input
              file.   Each  black  pixel in pbmfile means that the value of the corresponding pixel in the input
              file is irrelevant.  The IW44 encoder will replace the masked pixels by a color value whose coding
              cost  is  minimal  (see  http://www.djvuzone.org/djvu/techpapers/mask/index.djvu   for   technical
              details.)

       -crcbnormal
              Select  normal chrominance encoding.  Chrominance information is encoded at the same resolution as
              the luminance.  This is the default.

       -crcbhalf
              Selects half resolution chrominance encoding.  Chrominance information  is  encoded  at  half  the
              luminance resolution.

       -crcbdelay n
              This  option  can  be used with -crcbnormal and -crcbhalf to modify the quality of the chrominance
              information.  The option arguments specifies a parameter n, expressed in slices, that reduces  the
              bit-rate associated with the chrominance.  The default chrominance encoding delay is 10 slices.

       -crcbfull
              Select  the  highest possible quality for encoding the chrominance information. This is equivalent
              to specifying -crcbnormal and -crcbdelay 0.

       -crcbnone
              Disable the encoding of the chrominance.  Only the luminance  information  will  be  encoded.  The
              resulting image will show in shades of gray.

REMARKS

       The default quality setting of the DjVuLibre version of c44 has been increased.  It produces larger files
       with a better quality.  Quality can be lowered using the quality selection options!

BUGS

       The encoder requires more memory than necessary.
       The rechunking capability is currently broken.

CREDITS

       This  program  was  written  by Léon Bottou <leonb@users.sourceforge.net> and was then improved by Andrei
       Erofeev <andrew_erofeev@yahoo.com>, Bill Riemers <docbill@sourceforge.net> and many others.

SEE ALSO

       djvu(1), pnm(5), cjpeg(1).

DjVuLibre-3.5                                      10/11/2001                                             C44(1)