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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 sug‐
       gested 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 coeffi‐
       cients.	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 com‐
       pression 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"  con‐
       taining	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  num‐
       ber 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) indi‐
	      cating 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  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	 cumu‐
	      lative  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-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 differ‐
	      ent according to the format of the input image (raw or JPEG com‐
	      pressed).

       -decibel n,...,n
	      Specify quality targets for each chunk expressed as a comma-sep‐
	      arated list of increasing decibel values.	 Decibel values	 range
	      from 16 (very low quality) to 48 (very high quality).  This cri‐
	      terion should not be relied upon when re-encoding an image  pre‐
	      viously  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 speci‐
       fication options are allowed.  The program outputs a file  whose	 total
       number  of chunks is the largest number of chunks of all quality speci‐
       fications.  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 argu‐
	      ments 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)
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