giftopnm(1) - phpMan

giftopnm(1) General Commands Manual giftopnm(1)

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 im-
age contains other colors, the output 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 al-
pha-filename file contains all zero (transparent) alpha values. If you don't spec-
ify --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 Out-
put 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 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(1), ppmcolormask(1), pnmcomp(1), gifsicle(1) <http://www.lcdf.org/gifsicle>,
ppm(5).

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 en-
forced the patent against trivial users, and has made statements that it is much less con-
cerned 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 for-
mat.

13 January 2001 giftopnm(1)

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