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giftopnm General Commands Manual giftopnm

NAME

giftopnm – convert a GIF file into a portable anymap

SYNOPSIS

giftopnm [–alphaout={alpha-filename,-}] [-verbose] [-comments] [-image
N] [GIFfile]

DESCRIPTION

This is a graphics format converter from the GIF format to the PNM
(i.e. PBM, PGM, or PPM) format.

If the image contains only black and maximally bright white, the output
is PBM. If the image contains more than those two colors, but only
grays, the output is PGM. If the image contains other colors, the out‐
put is PPM.

If you have an animated GIF file, you can extract individual frames
from it with gifsicle and then convert those using giftopnm.

A GIF image contains rectangular pixels. They all have the same aspect
ratio, but may not be square (it’s actually quite unusual for them not
to be square, but it could happen). The pixels of a Netpbm image are
always square. Because of the engineering complexity to do otherwise,
giftopnm converts a GIF image to a Netpbm image pixel-for-pixel. This
means if the GIF pixels are not square, the Netpbm output image has the
wrong aspect ratio. In this case, giftopnm issues an informational
message telling you to run pnmscale to correct the output.

OPTIONS

–alphaout=alpha-filename
giftopnm creates a PGM (portable graymap) file containing the
alpha channel values in the input image. If the input image
doesn’t contain an alpha channel, the alpha-filename file con‐
tains all zero (transparent) alpha values. If you don’t specify
–alphaout, giftopnm does not generate an alpha file, and if the
input image has an alpha channel, giftopnm simply discards it.

If you specify – as the filename, giftopnm writes the alpha out‐
put to Standard Output and discards the image.

See pnmcomp for one way to use the alpha output file.

-verbose
Produce verbose output about the GIF file input.

-comments
Only output GIF89 comment fields.

-image N
Output the specified gif image from the input GIF archive (where
N is ‘1’, ‘2’, ’20’…). Normally there is only one image per
file, so this option is not needed.

All flags can be abbreviated to their shortest unique prefix.

RESTRICTIONS
This does not correctly handle the Plain Text Extension of the GIF89
standard, since I did not have any example input files containing them.

SEE ALSO

ppmtogif, ppmcolormask, pnmcomp, gifsicle(1)
, ppm(5).

AUTHOR

Copyright (c) 1993 by David Koblas (koblas@netcom.com)

LICENSE
If you use giftopnm, you are using a patent on the LZW compression
method which is owned by Unisys, and in all probability you do not have
a license from Unisys to do so. Unisys typically asks $5000 for a
license for trivial use of the patent. Unisys has never enforced the
patent against trivial users, and has made statements that it is much
less concerned about people using the patent for decompression (which
is what giftopnm does than for compression. The patent expires in 2003
/ 2004, depending on the country.

Rumor has it that IBM also owns a patent covering giftopnm.

A replacement for the GIF format that does not require any patents to
use is the PNG format.

13 January 2001 giftopnm