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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)