giftopnm(1)giftopnm(1)NAMEgiftopnm - convert a GIF file into a portable anymap
SYNOPSISgiftopnm [--alphaout={alpha-filename,-}] [-verbose] [-com
ments] [-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 output is PPM.
If you have an animated GIF file, you can extract individ
ual 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 actu
ally 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 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 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 pre
fix.
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 ALSOppmtogif(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, and has made statements that it is
much less concerned about people using the patent for
decompression (which is what giftopnm does than for com
pression. 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.
13 January 2001 giftopnm(1)
