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OpenSolaris 2009.06 - man page for djpeg (opensolaris section 1)

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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 cur-
       rently supported:

	 o  BMP

	 o  GIF

	 o  PGM, the PBMPLUS gray-scale format

	 o  PPM, the PBMPLUS color format

	 o  RLE, the Utah Raster Toolkit format

	 o  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 col-
		       ormapped format is displayed if -colors 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 colormapped display or stored in a colormapped file format. For exam-
		       ple, if you have an 8-bit display, you must reduce to 256 colors or less.

		       You can also use -quantize to specify this option. However, -colors is the
		       recommended option name. The -quantize option is provided only  for  back-
		       wards compatibility.

       -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 col-
		       ormapped format is displayed if -colors 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 dis-
		       played if -grayscale is specified, or if the JPEG file is grayscale.  Col-
		       ormapped  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 everywhere.

       -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 dithering is  fast  but  is
		       usually	of poor quality. This option has no effect unless color quantiza-
		       tion is being done.

       -dither ordered Use ordered dithering in color quantization. Ordered dither is  a  compro-
		       mise  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  predefined 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 processing 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 out-
		       put.

       -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 specify  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  recom-
       mended settings.

       The -dct fast and -nosmooth options gain speed for a small sacrifice in quality. When pro-
       ducing 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 seldom 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 theoretical accuracy advantage is too small to be  significant
       in practice.

EXAMPLES
       Example	1: Decompressing the JPEG File test.jpg, Quantizing to 256 Colors, 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 specified as described for the -maxmem-
			       ory 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		     |SUNWjpg			   |
       +-----------------------------+-----------------------------+
       |Interface stability	     |Uncommitted		   |
       +-----------------------------+-----------------------------+

SEE ALSO
       Wallace, Gregory K., The JPEG Still Picture Compression	Standard  Communications  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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