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)