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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 com-
       pression 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 render-
       ing and smooth scrolling of large images with limited memory requirements.  Decoding func-
       tions  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 vari-
       ous  state-of-the-art  wavelet  compression  schemes.   Although these schemes may achieve
       slightly smaller file sizes, the decoding functions did not  even  approach  our  require-
       ments.	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 specifica-
       tion.  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-sep-
	      arated 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 photo-
	      graphic image with three progressive refinements.  More quality  and  more  refine-
	      ments 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  sug-
	      gested 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 tar-
	      gets 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-sepa-
	      rated and plus-separated specifications are accepted.  Option -bpp 0.25,0.5,1  usu-
	      ally 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-repre-
	      sented blocks of 32 x 32 pixels.	This option is useful with composite images  con-
	      taining solid color features (e.g. an image with a large white border).

       Providing  no quality specification options automatically selects a default quality speci-
       fication -slice 74,89,99.  Multiple quality specification options are allowed.	The  pro-
       gram  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  photo-
	      graphic images.

       -gamma n
	      Specify  the  gamma correction information encoded into the output file.	The argu-
	      ment 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 techni-
	      cal 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  pro-
       duces larger files with a better quality.  Quality can be lowered using the quality selec-
       tion options!

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

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

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

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