ppmtogif(1)

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)

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