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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 produces a JPEG/JFIF file on the  standard	 output.   The
       following input file formats are currently supported:

	 ·  BMP

	 ·  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:

       -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 encod‐
			       ing  parameters	are  used.  -optimize  usually
			       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 infor‐
			       mation  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
			       Description 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 inte‐
			       ger methods should give the same results every‐
			       where.

       -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 standard 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  information about the -smooth option, see
			       the Extended Description section.

       -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 qual‐
       ity  setting  that  decompresses	 into an output image that is visually
       indistinguishable from the original image. For this purpose, the	 qual‐
       ity  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 qual‐
       ity 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	 stan‐
       dard.  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  -baseline 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 qual‐
       ity. 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 imple‐
       mented, 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 compression of full-color 24-bit images. In particu‐
       lar, 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 experi‐
       ment  with  the -quality and -smooth options to get a satisfactory con‐
       version. A value of -smooth 10 is often helpful.

       Avoid running an image through a series of JPEG	compression/decompres‐
       sion  cycles. Image quality loss will accumulate. After ten cycles, the
       image may be noticeably worse than it was after one cycle. Use a	 loss‐
       less  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 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.

       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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