NAME

djpeg − JPEG Decompressor

SYNTAX

djpeg [-G] [-b] [-g] [-q N] [-D] [-2] [-d]

DESCRIPTION

djpeg decompresses a 24-bit image. 

OPTIONS

The command line switches for djpeg are:

-G Select GIF output format (implies -q, with default of 256 colors). 

-b Perform cross-block smoothing.  This is quite memory-intensive and only seems to improve the image at very low quality settings (-Q 10 to 20 or so). 

-g Force gray-scale output even if input is color. 

-q NQuantize to N colors. 

-D Use Floyd-Steinberg dithering in color quantization. 

-2 Use two-pass color quantization (not yet supported). 

-d Enable debug printout.  More -d’s give more printout. 

BUGS

Color quantization currently uses a rather shoddy algorithm (although it’s not so horrible when dithered).  Because of this, the GIF output mode is not recommended in the current release, except for gray-scale output.  You can get better results by applying ppmquant to the unquantized (PPM) output of djpeg, then converting to GIF with ppmtogif.  We expect to provide a considerably better quantization algorithm in a future release. 

Note that djpeg ∗can∗ read noninterleaved JPEG files even though cjpeg can’t yet generate them.  For most applications this is a nonissue, since hardly anybody seems to be using noninterleaved format. 

On a non-virtual-memory machine, you may run out of memory if you use -q N -2 in djpeg, or try to read an interlaced GIF file.  This will be addressed eventually by replacing jvirtmem.c with something that uses temporary files for large images. 

SEE ALSO

cjpeg(1X)

The file README in /usr/src/X/contrib/clients/jpeg.  (In the Xsource package). 

COPYRIGHT

This software is copyright (C) 1991, Thomas G. Lane. 
All Rights Reserved except as specified below.

Permission is hereby granted to use, copy, modify, and distribute this software (or portions thereof) for any purpose, without fee, subject to these conditions:

(1) If any part of the source code for this software is distributed, then this README file must be included, with this copyright and no-warranty notice unaltered; and any additions, deletions, or changes to the original files must be clearly indicated in accompanying documentation. 

(2) If only executable code is distributed, then the accompanying documentation must state that "this software is based in part on the work of the Independent JPEG Group". 

(3) Permission for use of this software is granted only if the user accepts full responsibility for any undesirable consequences; the authors accept NO LIABILITY for damages of any kind. 

Permission is NOT granted for the use of any author’s name or author’s company name in advertising or publicity relating to this software or products derived from it.  This software may be referred to only as "the Independent JPEG Group’s software". 

Amiga Unix  —  Last change: Independent JPEG Group