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djpeg(1)			 User Commands			      djpeg(1)

NAME
       djpeg - decompress a JPEG file to an image file

SYNOPSIS
       djpeg [options] [filename]

DESCRIPTION
       djpeg  decompresses  the	 named	JPEG file, or the standard input if no
       file is named, and produces an image file on the standard output.   The
       following output file formats are currently supported:

	 ·  BMP

	 ·  GIF

	 ·  PGM, the PBMPLUS gray-scale format

	 ·  PPM, the PBMPLUS color format

	 ·  RLE, the Utah Raster Toolkit format

	 ·  Targa

       RLE is supported only if the URT library is available.

OPTIONS
       All  options may be abbreviated. For example, -grayscale may be written
       -gray or -gr.  Upper and lower case are equivalent. For	example,  -BMP
       is  the same as -bmp. British spellings are also accepted. For example,
       -greyscale.

   Basic Options
       The following basic options are supported:

       -bmp	       Specify that the output file is in BMP format,  Windows
		       flavor.	8-bit colormapped format is displayed if -col‐
		       ors or -grayscale is specified, or if the JPEG file  is
		       grayscale.  Otherwise, 24-bit full-color format is dis‐
		       played.

       -colors N       Reduce the image to at  most  N	colors.	  This	option
		       reduces	the number of colors used in the output image,
		       so that the output image can be	displayed  on  a  col‐
		       ormapped	 display  or stored in a colormapped file for‐
		       mat. For example, if you have  an  8-bit	 display,  you
		       must reduce to 256 colors or less.

		       You can also use -quantize to specify this option. How‐
		       ever, -colors  is  the  recommended  option  name.  The
		       -quantize option is provided only for backwards compat‐
		       ibility.

       -fast	       Select the recommended  processing  options  for	 fast,
		       low-quality  output. The default options are chosen for
		       highest quality output. Currently, this	is  equivalent
		       to -dct fast -nosmooth -onepass -dither ordered.

       -gif	       Specify that the output file is in GIF format. GIF does
		       not support more than 256 colors,  so  -colors  256  is
		       assumed unless you specify a smaller number of colors.

       -grayscale      Create a monochrome image file even if the JPEG file is
		       a color file. This option is useful for viewing	images
		       on monochrome displays. djpeg runs noticeably faster in
		       this mode.

       -os2	       Specify that the output file is in BMP format, OS/2 1.x
		       flavor.	8-bit colormapped format is displayed if -col‐
		       ors or -grayscale is specified, or if the JPEG file  is
		       grayscale.  Otherwise, 24-bit full-color format is dis‐
		       played.

       -pnm	       Specify that the output file is in PBMPLUS format.  PGM
		       format  is  displayed if -grayscale is specified, or if
		       the JPEG file is grayscale. Otherwise,  PPM  format  is
		       displayed.

       -rle	       Specify	that  the  output  file is in RLE format. This
		       option requires the URT library.

       -scale M/N      Scale the output image by a factor M/N. Currently,  the
		       scale  factor must be 1/1, 1/2, 1/4, or 1/8. Scaling is
		       useful if the image is larger than  your screen.	 djpeg
		       runs much faster when scaling down the output.

       -targa	       Specify	that  the  output  file	 is  in	 Targa format.
		       Grayscale format is displayed if -grayscale  is	speci‐
		       fied,  or  if  the  JPEG file is grayscale. Colormapped
		       format is displayed if -colors is specified. Otherwise,
		       24-bit full-color format is displayed.

   Intermediate Options
       The following intermediate options are supported:

       -dct fast       Use  the	 fast  integer DCT method. This method is less
		       accurate than the integer DCT method or	the  floating-
		       point DCT method.

       -dct float      Use  the floating-point DCT method. The float method is
		       very slightly more accurate than the int method, but is
		       much slower unless your machine has very fast floating-
		       point  hardware.	 The  results  of  the	floating-point
		       method  may  vary  slightly  across machines, while the
		       integer methods should give  the	 same  results	every‐
		       where.

       -dct int	       Use the integer DCT method. This is the default method.

       -dither fs      Use Floyd-Steinberg dithering in color quantization. By
		       default,	 Floyd-Steinberg  dithering  is	 applied  when
		       quantizing  colors.  This  process  is slow but usually
		       produces the best results. This option  has  no	effect
		       unless color quantization is being done.

       -dither none    Do  not use dithering in color quantization. No dither‐
		       ing is fast but is usually of poor quality. This option
		       has no effect unless color quantization is being done.

       -dither ordered Use  ordered  dithering	in color quantization. Ordered
		       dither is  a  compromise	 between  speed	 and  quality.
		       Ordered dither is only available in -onepass mode. This
		       option has no effect unless color quantization is being
		       done.

       -map file       Quantize	 to  the  colors  used	in the specified image
		       file. This option  is  useful  for  producing  multiple
		       files  with identical color maps, or for forcing a pre‐
		       defined set of colors to be used. file must be a GIF or
		       PPM   file.  This  option  overrides  the  -colors  and
		       -onepass options.

       -maxmemory N    Set the limit for the amount of memory to use  in  pro‐
		       cessing	large  images.	N is specified in thousands of
		       bytes, or in millions of bytes if "M" is specified with
		       the number. For example, -max 4m selects 4000000 bytes.
		       If more space is needed, temporary files are used.

       -nosmooth       Use a faster, lower-quality upsampling routine.

       -onepass	       Use one-pass instead of	two-pass  color	 quantization.
		       The one-pass method is faster and requires less memory,
		       but produces a lower-quality image. The -onepass option
		       is  ignored  unless  you	 also  specify	the  -colors N
		       option.	The  one-pass  method  is  always   used   for
		       grayscale  output,  the	two-pass  method  provides  no
		       improvement for such output.

       -outfile name   Send the output image to the named file, instead of  to
		       the standard output.

       -verbose	       Display	version	 information  at  startup,  and enable
		       debug printout. The -vv option  displays	 more  verbose
		       output than the -v option. The -vvv option displays the
		       most verbose output.  You can also use -debug to	 spec‐
		       ify the verbose option.

OPERANDS
       The following operands are supported:

       filename	       The name of the JPEG file to be decompressed.

EXTENDED DESCRIPTION
   Hints
       To  get	a  quick  preview  of  an  image, use the -grayscale or -scale
       options, or a combination of  both  options.  For  example,  -grayscale
       -scale 1/8 is the fastest case.

       Several	options	 trade	image  quality to gain speed. The -fast option
       configures the recommended settings.

       The -dct fast and -nosmooth options gain speed for a small sacrifice in
       quality.	 When  producing  a  color-quantized  image,  -onepass -dither
       ordered is fast but much	 lower	quality	 than  the  default  behavior.
       -dither	none may give acceptable results in two-pass mode, but is sel‐
       dom tolerable in one-pass mode.

       If you have very fast floating point hardware, -dct float may  be  even
       faster  than -dct fast. However, on most machines, -dct float is slower
       than -dct int. In such cases, do not use -dct float, because the	 theo‐
       retical accuracy advantage is too small to be significant in practice.

EXAMPLES
       Example 1: Decompressing the JPEG File test.jpg, Quantizing to 256 Col‐
       ors, and Saving the Output in 8-bit BMP Format as test.bmp

       example% djpeg -colors 256 -bmp test.jpg > test.bmp

ENVIRONMENT VARIABLES
       djpeg uses the following environment variables:

       JPEGMEM		       The value of this environment variable, if set,
			       is the default memory limit. The value is spec‐
			       ified as described for the  -maxmemory  option.
			       JPEGMEM	overrides  the default value specified
			       when the program was compiled, and is  in  turn
			       overridden by an explicit -maxmemory option.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌─────────────────────────────┬─────────────────────────────┐
       │      ATTRIBUTE TYPE	     │	    ATTRIBUTE VALUE	   │
       ├─────────────────────────────┼─────────────────────────────┤
       │Availability		     │image/library/libjpeg	   │
       ├─────────────────────────────┼─────────────────────────────┤
       │Interface stability	     │Uncommitted		   │
       └─────────────────────────────┴─────────────────────────────┘

SEE ALSO
       Wallace, Gregory K., The JPEG Still Picture Compression Standard Commu‐
       nications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.

       cjpeg(1), jpegtran(1), rdjpgcom(1), wrjpgcom(1)

NOTES
       Arithmetic coding is not supported.  djpeg  produces  uncompressed  GIF
       files. These large files are readable by standard GIF decoders.

       This  man  page	was  originally written by the Independent JPEG Group.
       Updated by Breda McColgan, Sun Microsystems Inc., 2004.

SunOS 5.11			  26 Mar 2004			      djpeg(1)
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