giftopnm - convert a GIF file into a portable anymap
SYNOPSIS
giftopnm [--alphaout={alpha-filename,-}] [-verbose] [-com
ments] [-image N] [GIFfile]
DESCRIPTION
Reads a GIF file for input, and outputs portable anymap.
If you have an animated GIF file, you can extract individ
ual frames from it with gifsicle and then convert those
using giftopnm.
If the image identifies a transparent background color
(i.e. a color that a user of the image should treat as
transparent in the event that the image is overlaid over
another), giftopnm issues a message telling you what color
that is when you use the -verbose option. You can then
use ppmcolormask to create a PGM file representing a
transparency mask and use that PGM file with other Netpbm
programs to effect transparency.
OPTIONS
--alphaout=alpha-filename
giftopnm creates a PGM (portable graymap) file con
taining the alpha channel values in the input
image. If the input image doesn't contain an alpha
channel, the alpha-filename file contains 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 output to Standard Output and discards
the image.
See pnmcomp(1) 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 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.
fix.
BUGS
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(1), ppmcolormask(1), pnmcomp(1), gifsicle(1)
<http://www.lcdf.org/gifsicle>, 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. The patent expires in 2003.
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.
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