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C44(1)                           DjVuLibre-3.5                          C44(1)



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  val-
              ues  (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)  indi-
              cating  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-sepa-
              rated  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-sepa-
              rated 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-sepa-
              rated 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 resolu-
              tion information encoded in DjVu files determine how the decoder scales the image on a  particular  dis-
              play.  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 informa-
              tion.  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 Leon Bottou <leonbATusers.net> and was then improved by  Andrei  Erofeev
       <andrew_erofeevATyahoo.com>, Bill Riemers <docbillATsourceforge.net> and many others.

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



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