NAME
    ppmtogif - convert a portable pixmap into a GIF file

SYNOPSIS
    ppmtogif [-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 designate 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 combine multiple
    GIF images into an animated GIF, use 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 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 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 equidistant, ppmtogif chooses one of them arbitrar-
    ily.

    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 trans-
    parency.  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.

    -nolzw 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 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 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 has expressed far less interest in enforc-
    ing the patent on decoding than on encoding.

SEE ALSO
   giftopnm(1),  ppmquant(1),    pngtopnm(1),   gifsicle(1)
    <http://www.lcdf.org/gifsicle>, ppm(5).

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, 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 ppmtogif.

    A replacement for the GIF format that does not require any patents to
    use is the PNG format.