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C44(1)				 DjVuLibre-3.5				C44(1)

       c44 - DjVuPhoto encode.

       c44 [options] inputfilename [outputfilename]

       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.

       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

       -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

       -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 op-
	      tion  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  ac-
	      cepted.  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-

       -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  de-
       fault quality specification -slice 74,89,99.  Multiple quality specifi-
       cation 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.

       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	   for
	      technical	details.)

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

	      Selects  half  resolution	chrominance encoding.  Chrominance in-
	      formation	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.

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

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

       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!

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

       This program was	written	by Leon	 Bottou	 <>
       and  was	 then  improved	 by Andrei Erofeev <>,
       Bill Riemers <> and many others.

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

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


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