NAME

cjpeg − JPEG Compressor

SYNTAX

cjpeg [-I] [-a] [-o] [-Q quality] [-d]

DESCRIPTION

cjpeg compresses a 24-bit image. 

OPTIONS

The command line switches for cjpeg are:

-I
Generate noninterleaved JPEG file (not yet supported).

-Q quality
Scale quantization tables to adjust quality.  quality is 0 (worst) to 100 (best); default is 75.  (See the README file for more information.) 

-a Use arithmetic coding rather than Huffman coding. (Not currently supported, see LEGAL ISSUES in the README file.) 

-o Perform optimization of entropy encoding parameters.  Without this, default Huffman or arithmetic parameters are used.  -o makes the JPEG file a tad smaller, but compression uses much more memory.  Image quality is unaffected by -o. 

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

Currently supported image file formats include raw-format PPM, raw-format PGM (for monochrome images), and GIF.  cjpeg recognizes the input image format automatically, but you have to tell djpeg which format to generate. 

Typically you’d use -Q settings of 50 or 75 or so.  -Q 100 will generate a quantization table of all 1’s, meaning no quantization loss; then any differences between input and output images are due to subsampling or to roundoff error in the DCT or colorspace-conversion steps.  -Q values below 50 may be useful for making real small, low-quality images.  Try -Q 2 (or so) for some amusing Cubist effects.  (Note that -Q values below about 25 generate 2-byte quantization tables, which are not decodable by pure baseline JPEG decoders.  cjpeg emits a warning message when you give such a -Q value.) 

SEE ALSO

djpeg(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