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 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.

       -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 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 decompressor would see this as a particular case of LZW compression.

              Note that if someone uses an LZW decompressor such as the one in ppmtogif 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 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>.  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 ppmtogif.

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

                                           20 May 2000                                ppmtogif(1)