PNMTOLJPG(1)

NAME
pnmtoljpg - compress a Portable Pixmap or Portable Graymap image file to a lossless JPEG file

SYNOPSIS
pnmtoljpg [ -d ] [ -h ] [ -p# ] [ -r# ] [ -s{1..7} ] [ -v ] [ filename ... ]

DESCRIPTION

pnmtoljpg compresses a PPM (Portable Pixmap) or a PGM (Portable Graymap) image, and produces a lossless JPEG (LJPG) file. If no files are specified, the standard input is compressed to the standard output.

OPTIONS

-d  Use default Huffman table. If this flag is not specified, pnmtoljpg will generate an optimal Huffman table.

-h --help
    Display a help screen and quit.

-p# The #, an integer less than sample precision bits, is the point tranform parameter.

-r# Restart at every # row(s).

-s{1..7}
    Supply a prediction selection value (PSV) set, {1..7}. The pnmtoljpg tries all PSVs in the set and select the best one. A PSV is an integer between 1 and 7 inclusively. If a "-s" flag is not provided, pnmtoljpg will try all seven PSVs.

-v verbose
    Display data about image format, image size, sample precision, total bytes category symbols, total bytes of additional symbols, original and compressed file size, and compress ratio.

EXAMPLES

This example compresses a PPM file foo.ppm with optimal Huffman table and the default PSV set. The output is foo.ljpg.

    pnmtoljpg foo.ppm foo.ljpg

Next example compresses a PGM file foo.pgm with default Huffman table and PSV 4. The output is saved as foo.ljpg.

    pnmtoljpg -d -s4 < foo.ppm > foo.ljpg

The last example compresses a PPM file foo.ppm with optimal Huffman table and a PSV set {246}. The verbose flag is on, and the output is saved as foo.ljpg.

    pnmtoljpg -v -s246 foo.ppm > foo.ljpg

SEE ALSO
ljpgtopnm(1), ppm(5), pgm(5)
Wallace, Gregory K. "The JPEG Still Picture Compression Standard", Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.

AUTHOR
Kongji Huang and Brian Smith

BUGS
Arithmetic coding and multiple scans are not supported.

Comments in PPM/PGM files are not stored in the LJPG files.