Ppmtogif User Manual(0) Ppmtogif User Manual(0)NAMEppmtogif - convert a PPM image to a GIF image
SYNOPSISppmtogif
[-interlace]
[-sort]
[-mapfile mapfile] [-transparent=[=]color]
[-alpha=pgmfile]
[-comment=text]
[-nolzw] [ppmfile]
All options can be abbreviated to their shortest unique prefix. You
may use two hyphens instead of one to designate an option. You may use
either white space or equals signs between an option name and its
value.
DESCRIPTION
This program is part of Netpbm(1).
ppmtogif reads a PPM iamge as input and produces a GIF file as output.
This program creates only individual GIF images. To combine multiple
GIF images into an animated GIF, use gifsicle
⟨http://www.lcdf.org/gifsicle/⟩ (not part of the Netpbm package).
ppmtogif creates either an original GIF87 format GIF file or the newer
GIF89 format. It creates GIF89 when you request features that were new
with GIF89, to wit the -transparent or -comment options. Otherwise, it
creates GIF87. Really old GIF readers conceivably could not recognize
GIF89.
OPTIONS-interlace
Produce an interlaced GIF file.
-sort Produce a GIF file with a sorted color map.
-mapfile=mapfile
Use the colors found in the file mapfile to create the colormap
in the GIF file, instead of the colors from ppmfile. mapfile
can be any PPM file; all that matters is the colors in it. If
the colors in ppmfile do not match those in mapfile, ppmtogif
matches them to a 'best match.' You can obtain a much better
result by using pnmremap to change the colors in the input to
those in the map file.
The mapfile file is not a palette file, just an image whose col‐
ors you want to use. The order of colors in the GIF palette
have nothing to do with where they appear in the mapfile image,
and duplication of colors in the image is irrelevant.
-transparent=color
ppmtogif marks the specified color as transparent in the GIF
image.
If you don't specify -transparent, ppmtogif does not mark any
color transparent (except as indicated by the -alpha option).
Specify the color (color) as described for the argument of the
ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ .
If the color you specify is not present in the image, ppmtogif
selects instead the color in the image that is closest to the
one you specify. Closeness is measured as a cartesian distance
between colors in RGB space. If multiple colors are equidis‐
tant, ppmtogif chooses one of them arbitrarily.
However, if you prefix your color specification with '=', e.g.
-transparent==red, only the exact color you specify will be
transparent. If that color does not appear in the image, there
will be no transparency. ppmtogif issues an information message
when this is the case.
You cannot specify both -transparent and -alpha.
-alpha=pgmfile
This option names a PGM file that contains an alpha mask for
the image. ppmtogif creates fully transparent pixels wherever
the alpha mask indicates transparency greater than 50%. The
color of those pixels is that specified by the -alphacolor
option, or black by default.
To do this, ppmtogif creates an entry in the GIF colormap in
addition to the entries for colors that are actually in the
image. It marks that colormap entry as transparent and uses
that colormap index in the output image to create a transparent
pixel.
The alpha image must be the same dimensions as the input image,
but may have any maxval. White means opaque and black means
transparent.
You cannot specify both -transparent and -alpha.
-alphacolor
See -alpha.
-comment=text
Include a comment in the GIF output with comment text text.
Without this option, there are no comments in the output.
Note that in a command shell, you'll have to use quotation marks
around text if it contains characters (e.g. space) that would
make the shell think it is multiple arguments:
$ ppmtogif-comment "this is a comment" <xxx.ppm >xxx.gif
-nolzw
This option is mainly of historical interest -- it involves use
of a patent that is now expired.
This option causes the GIF output, and thus ppmtogif, not to use
LZW (Lempel-Ziv) compression. As a result, the image file is
larger and, before the patent expired, no royalties would be
owed to the holder of the patent on LZW. See the section
LICENSE below.
LZW is a method for combining the information from multiple pix‐
els into a single GIF code. With the -nolzw option, ppmtogif
creates one GIF code per pixel, so it is not doing any compres‐
sion and not using LZW. However, any GIF decoder, whether it
uses an LZW decompressor or not, will correctly decode this
uncompressed format. An LZW decompressor would see this as a
particular case of LZW compression.
Note that if someone uses an LZW decompressor such as the one in
giftopnm or pretty much any graphics display program to process
the output of ppmtogif-nolzw , he is then using the LZW patent.
But the patent holder expressed far less interest in enforcing
the patent on decoding than on encoding.
SEE ALSOgiftopnm(1), ppmquant(1), pngtopnm(1),
gifsicle http://www.lcdf.org/gifsicle ⟨http://www.lcdf.org/gifsicle⟩ ,
ppm(1).
AUTHOR
Based on GIFENCOD by David Rowley <mgardi@watdcsu.waterloo.edu>. Lem‐
pel-Ziv compression based on 'compress'.
The non-LZW format is generated by code based on djpeg by the Indepen‐
dent Jpeg Group.
Copyright (C) 1989 by Jef Poskanzer.
LICENSE
If you use ppmtogif without the -nolzw option, you are using a patent
on the LZW compression method which is owned by Unisys. The patent has
expired (in 2003 in the US and in 2004 elsewhere), so it doesn't mat‐
ter. While the patent was in force, most people who used ppmtogif and
similar programs did so without a license from Unisys to do so. Unisys
typically asked $5000 for a license for trivial use of the patent.
Unisys never enforced the patent against trivial users.
Rumor has it that IBM also owns or owned a patent covering ppmtogif.
A replacement for the GIF format that never required any patents to use
is the PNG format.
netpbm documentation 15 September 2002 Ppmtogif User Manual(0)
