ppmtogif man page on Debian

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ppmtogif(1)							   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  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	trans‐
	      parency.	 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 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
	      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 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)
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