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

cjpeg(1)				  User Commands 				 cjpeg(1)

NAME
       cjpeg - compress an image file to a JPEG file

SYNOPSIS
       cjpeg [options] [filename]

DESCRIPTION
       cjpeg compresses the named image file, or the standard input if no file is named, and pro-
       duces a JPEG/JFIF file on the standard output.  The following input file formats are  cur-
       rently supported:

	 o  BMP

	 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:

       -grayscale	       Create  a  monochrome  JPEG  file from color input. You should use
			       this switch when compressing a grayscale BMP file,  because  cjpeg
			       cannot  detect  whether	a  BMP	file uses only shades of gray. By
			       specifying the -grayscale option, you create a smaller  JPEG  file
			       that takes less time to process.

       -optimize	       Optimize  the  entropy  encoding parameters. If you do not specify
			       this option, default encoding parameters are used. -optimize  usu-
			       ally  makes  the  JPEG  file a little smaller, but cjpeg runs more
			       slowly and needs much more memory.  Image  quality  and	speed  of
			       decompression are unaffected by the -optimize option.

       -progressive	       Create  a  progressive  JPEG  file. For more information about the
			       -progressive option, see the Extended Description section.

       -quality N	       Scale the quantization tables to adjust image  quality.	N  ranges
			       from  0	(worst)  to 100 (best). The default value is 75. For more
			       information about the -quality option, see the  Extended  Descrip-
			       tion section.

       -targa		       Specify	that  the input file is in Targa format. Targa files that
			       contain an "identification" field are not automatically recognized
			       by  cjpeg.  For	such files, you must specify -targa to make cjpeg
			       treat the input as Targa format. For most Targa files, you do  not
			       need this switch.

   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.

       -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.

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

       -restart N	       Emit a JPEG restart marker every N MCU rows, or every N MCU blocks
			       if "B" is specified with the number. The default value is -restart
			       0, which means no restart markers. For more information about  the
			       -restart option, see the Extended Description section.

       -smooth N	       Smooth the input image to eliminate dithering noise. N ranges from
			       1 to 100, and indicates the strength of	smoothing.   The  default
			       value  is  -smooth 0, which means no smoothing.	For more informa-
			       tion about the -smooth option, see the Extended	Description  sec-
			       tion.

       -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 this option.

   Advanced Options
       The following advanced options are supported for advanced users only:

       -baseline	       Force  baseline-compatible  quantization  tables  to be generated.
			       This clamps the quantization values to 8 bits, even at low quality
			       settings.  This option is poorly named, because -baseline does not
			       ensure that the output is actually  baseline  JPEG.  For  example,
			       you can use the -baseline and -progressive options together.

       -qslots N[,...]	       Select which quantization table to use for each color component.

       -qtables file	       Use the quantization tables provided in the specified text file.

       -sample HxV[,...]       Set the JPEG sampling factors for each color component.

       -scans file	       Use the scan script provided in the specified text file.

OPERANDS
       The following operands are supported:

       filename 	       The name of the image file to be compressed.

EXTENDED DESCRIPTION
   The -quality Option
       The  -quality  option enables you to trade compressed file size against the quality of the
       reconstructed image: the higher the quality setting, the larger the  JPEG  file,  and  the
       greater	the similarity between the output image and the original input. Normally, you use
       the lowest quality setting that decompresses into an output image that is visually  indis-
       tinguishable  from  the	original  image.  For this purpose, the quality setting should be
       between 50 and 95. The default value of 75 is often just right.	If  you  see  defects  at
       -quality  75,  increase	the  quality  by 5 until you are happy with the output image. The
       optimal setting varies from one image to another.

       A value of -quality 100 generates a quantization table of ones. This minimizes loss in the
       quantization  step,  but  information  is  still  lost in subsampling, as well as roundoff
       error. The -quality 100 setting is mainly of interest for experimental  purposes.  Quality
       values  above 95 are not recommended for normal use, as the compressed file size increases
       dramatically for very little gain in output image quality.

       Quality values below 50 produce very small files of low image quality.  Settings of  5  to
       10  might  be  useful in preparing an index of a large image library, for example. Quality
       values below 25 generate 2-byte quantization tables, which are considered optional in  the
       JPEG  standard.	cjpeg  emits  a  warning  message  when you specify such a quality value,
       because some other JPEG programs might be unable to decode the resulting file. Use  -base-
       line if you need to ensure compatibility at low quality values.

   The -progressive Option
       The  -progressive option creates a "progressive JPEG" file. In this type of JPEG file, the
       data is stored in multiple scans of increasing quality. If the file is transmitted over	a
       slow  communications  link,  the  decoder  can use the first scan to display a low-quality
       image very quickly, and can then improve the display with each subsequent scan. The  final
       image  is  exactly equivalent to a standard JPEG file of the same quality setting, and the
       total file size is about the same, or a little smaller. Caution: progressive JPEG  is  not
       yet  widely  implemented,  so  many decoders are unable to view a progressive JPEG file at
       all.

   The -restart Option
       The -restart option inserts extra markers that allow a JPEG decoder to resynchronize after
       a  transmission	error.	Without  restart markers, any damage to a compressed file usually
       ruins the image from the point of the error to the end of the image. With restart markers,
       the  damage is usually confined to the portion of the image from the point of the error to
       the next restart marker. The restart markers occupy extra space. We recommend  -restart	1
       for images that are transmitted across unreliable networks.

   The -smooth Option
       The  -smooth  option filters the input to eliminate fine-scale noise. This option is often
       useful when you convert dithered images to JPEG: a moderate smoothing factor of 10  to  50
       deletes	dithering  patterns  from  the input file, resulting in a smaller JPEG file and a
       better-looking image. If the smoothing factor is too large, the image visibly blurs.

   Hints
       Color GIF files are not the ideal input for JPEG. JPEG is really intended for the compres-
       sion  of  full-color  24-bit  images.  In particular, do not try to convert cartoons, line
       drawings, or other images that have only a few distinct colors. GIF works well  on  these,
       but  JPEG  does not. If you want to convert a GIF file to JPEG, you should experiment with
       the -quality and -smooth options to get a satisfactory conversion. A value of  -smooth  10
       is often helpful.

       Avoid  running  an  image through a series of JPEG compression/decompression cycles. Image
       quality loss will accumulate. After ten cycles, the image may be noticeably worse than  it
       was  after  one	cycle. Use a lossless format while manipulating an image, then convert to
       JPEG format when you are ready to file the image away.

       Use the -optimize option when you make a "final" version for posting or	archiving.  Also,
       when  you use low quality settings, make very small JPEG files. The percentage improvement
       is often much greater than on larger files. At present, the  -optimize  option  is  always
       selected when generating progressive JPEG files.

EXAMPLES
       Example	1:  Compressing  the PPM File test.ppm With a Quality Factor of 60 and Saving the
       Output as test.jpg

       example% cjpeg -quality 60 test.ppm > test.jpg

ENVIRONMENT VARIABLES
       cjpeg 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.

       djpeg(1), jpegtran(1), rdjpgcom(1), wrjpgcom(1)

NOTES
       Arithmetic  coding  is not supported. GIF input files are not supported.  Not all variants
       of BMP and Targa file formats are supported.

       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					 cjpeg(1)


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