Provided by: djvulibre-bin_3.5.27.1-13_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).