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RedHat 9 (Linux i386) - man page for ppmtogif (redhat section 1)

ppmtogif(1)			     General Commands Manual			      ppmtogif(1)

       ppmtogif - convert a portable pixmap into a GIF file

       ppmtogif [-interlace] [-sort] [-map mapfile]
       [-transparent [=]color] [-alpha pgmfile] [-comment text] [-nolzw]

       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.

       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.

	      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 mat-
	      ters  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.


	      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 transpar-
	      ent 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.

	      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 giftopnm 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.

       giftopnm(1), ppmquant(1), pngtopnm(1), gifsicle(1) <http://www.lcdf.org/gifsicle>, ppm(5).

       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.

       If you use ppmtogif without the -nolzw option, you are using a patent on the LZW  compres-
       sion  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  for-

					   20 May 2000				      ppmtogif(1)

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