djpeg(1)

NAME

     djpeg - decompress a JPEG file to an image file

SYNOPSIS

     djpeg [ -colors N ] [ -gif ] [ -pnm ] [ -rle ] [ -targa ]  [
     -blocksmooth ] [ -grayscale ] [ -maxmemory N ] [ -nodither ]
     [ -onepass ] [ -verbose ] [ -debug ] [ 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.  PBMPLUS  (PPM/PGM),  GIF,  Targa,  or  RLE
     (Utah  Raster  Toolkit) output format can be selected.  (RLE
     is supported only if the URT library is available.)

OPTIONS

     All switch names may be abbreviated; for example, -grayscale
     may  be  written -gray or -gr.  Most of the "basic" switches
     can be abbreviated to as little as one  letter.   Upper  and
     lower  case  are equivalent (thus -GIF is the same as -gif).
     British spellings  are  also  accepted  (e.g.,  -greyscale),
     though for brevity these are not mentioned below.

     The basic switches are:

     -colors N
          Reduce image to at most N  colors.   This  reduces  the
          number  of  colors used in the output image, so that it
          can be displayed on a colormapped display or stored  in
          a colormapped file format.  For example, if you have an
          8-bit display, you'd need to reduce  to  256  or  fewer
          colors.

     -quantize N
          Same as -colors.   -colors  is  the  recommended  name,
          -quantize is provided only for backwards compatibility.

     -gif Select GIF output format.  Since GIF does  not  support
          more  than  256  colors, -colors 256 is assumed (unless
          you specify a smaller number of colors).

     -pnm Select PBMPLUS (PPM/PGM) output  format  (this  is  the
          default  format).   PGM  is emitted if the JPEG file is
          gray-scale or if -grayscale is specified; otherwise PPM
          is emitted.

     -rle Select RLE output format.  (Requires URT library.)

     -targa
          Select Targa output format.  Gray-scale format is emit-
          ted  if the JPEG file is gray-scale or if -grayscale is
          specified; otherwise, colormapped format is emitted  if
          -colors is specified; otherwise, 24-bit full-color for-
          mat is emitted.

     Switches for advanced users:

     -blocksmooth
          Perform cross-block smoothing.  This is  quite  memory-
          intensive  and  only seems to improve the image at very
          low quality settings (-quality 10 to  20  or  so).   At
          normal quality settings it may make the image worse.

     -grayscale
          Force gray-scale output even if  JPEG  file  is  color.
          Useful for viewing on monochrome displays.

     -maxmemory N
          Set limit for amount of memory  to  use  in  processing
          large  images.  Value is in thousands of bytes, or mil-
          lions of bytes if "M" is attached to the  number.   For
          example,  -max 4m selects 4000000 bytes.  If more space
          is needed, temporary files will be used.

     -nodither
          Do  not  use  dithering  in  color  quantization.    By
          default,  Floyd-Steinberg  dithering  is  applied  when
          quantizing colors, but on  some  images  dithering  may
          result in objectionable "graininess".  If that happens,
          you can turn off dithering with  -nodither.   -nodither
          is ignored unless you also say -colors N.

     -onepass
          Use one-pass instead of  two-pass  color  quantization.
          The  one-pass  method  is faster and needs less memory,
          but it produces a  lower-quality  image.   -onepass  is
          ignored  unless you also say -colors N.  Also, the one-
          pass method is always used for gray-scale  output  (the
          two-pass method is no improvement then).

     -verbose
          Enable debug printout.  More  -v's  give  more  output.
          Also, version information is printed at startup.

     -debug
          Same as -verbose.

EXAMPLES

     This example decompresses the JPEG file  foo.jpg,  automati-
     cally  quantizes  to 256 colors, and saves the output in GIF
     format in foo.gif:

          djpeg -gif foo.jpg > foo.gif

ENVIRONMENT

     JPEGMEM
          If this environment variable is set, its value  is  the
          default  memory  limit.   The  value  is  specified  as
          described for the -maxmemory switch.  JPEGMEM overrides
          the  default  value specified when the program was com-
          piled, and itself is overridden by  an  explicit  -max-
          memory.

SEE ALSO

AUTHOR

     Independent JPEG Group

BUGS

     Arithmetic coding is not supported for legal reasons.

     Still not as fast as we'd like.