ppmtogif

ppmtogif(1)                 General Commands Manual                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  ob-
              tained by using the following filter in advance:

              ppmquant -floyd -map mapfile

       -transparent color
              ppmtogif marks the specified color as transparent in the GIF im-
              age.

              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  transpar-
              ency.   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 ad-
              dition to the entries for colors that are actually in the image.
              It marks that colormap entry as transparent and uses  that  col-
              ormap 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 un-
              compressed format.  An LZW decompressor would see this as a par-
              ticular 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 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.

                                  20 May 2000                      ppmtogif(1)