ppmtogif(1)ppmtogif(1)NAMEppmtogif - convert a portable pixmap into a GIF file
SYNOPSISppmtogif [-interlace] [-sort] [-map 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 desig
nate an option. You may use either white space or equals
signs between an option name and its value.
DESCRIPTION
Reads a portable pixmap as input. Produces a GIF file as
output.
This program creates only individual GIF images. To com
bine multiple GIF images into an animated GIF, use gifsi
cle (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 rec
ognize GIF89.
OPTIONS-interlace
Produce an interlaced GIF file.
-sort Produces a GIF file with a sorted color map.
-map mapfile
Uses the colors found in the mapfile to create the
colormap in the GIF file, instead of the colors
from ppmfile. The 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 , they are
matched to a "best match." A (much) better result
can be obtained by using the following filter in
advance:
ppmquant -floyd -map mapfile
-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).
You specify the color as in ppmmake(1).E.g. red or
rgb:ff/00/0d. If the color you specify is not pre
sent 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 dis
tance between colors in RGB space. If multiple
colors are equidistant, 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 transpar
ent. 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 trans
parent 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 com
ments in the output.
-nolzw This option causes the GIF output, and thus ppm
togif, not to use LZW (Lempel-Ziv) compression. As
a result, the image file is larger and no royalties
are owed to the holder of the patent on LZW. See
the section LICENSE below.
LZW is a method for combining the information from
multiple pixels into a single GIF code. With the
-nolzw option, ppmtogif creates one GIF code per
pixel, so it is not doing any compression and not
using LZW. However, any GIF decoder, whether it
uses an LZW decompressor or not, will correctly
decode this uncompressed format. An LZW decompres
sor would see this as a particular case of LZW com
pression.
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 has expressed far less interest in
enforcing the patent on decoding than on encoding.
SEE ALSOgiftopnm(1), ppmquant(1), pngtopnm(1), gifsicle(1)
<http://www.lcdf.org/gifsicle>, ppm(5).
AUTHOR
Based on GIFENCOD by David Rowley <mgardi@watdcsu.water
loo.edu>. Lempel-Ziv compression based on "compress".
The non-LZW format is generated by code based on djpeg by
the Independent 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, 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 ppm
togif.
A replacement for the GIF format that does not require any
patents to use is the PNG format.
20 May 2000 ppmtogif(1)
