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giftopnm - convert a GIF file into a portable anymap
giftopnm
[--alphaout={alpha-filename,-}] [-verbose] [-comments] [-image N] [GIFfile]
Reads
a GIF file for input, and outputs portable anymap.
If you have an animated
GIF file, you can extract individual 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.
- --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 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.
All flags can be abbreviated to their shortest unique prefix.
This does not correctly handle the Plain Text Extension of the GIF89
standard, since I did not have any example input files containing them.
ppmtogif(1)
, ppmcolormask(1)
, pnmcomp(1)
, gifsicle(1)
<http://www.lcdf.org/gifsicle
>,
ppm(5)
.
Copyright (c) 1993 by David Koblas (koblas@netcom.com)
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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