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Pamtogif User Manual(0) 						  Pamtogif User Manual(0)

       pamtogif - convert a Netpbm image to a GIF image




       [-mapfile=mapfile] [-transparent=[=]color]





       [-verbose] [netpbmfile]

       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 an  equals  sign
       between an option name and its value.

       This program is part of Netpbm(1)

       pamtogif reads a Netpbm image as input and produces a GIF file as output.

       This  program  creates only individual GIF images.  To combine multiple GIF images into an
       animated GIF, use gifsicle <http://www.lcdf.org/gifsicle/>  (not part of the Netpbm  pack-

       pamtogif  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.

       The GIF format is not capable of representing an image with more than 256 colors in it (it
       contains  a  color  map with a maximum size of 256).  If the image you want to convert has
       more colors than that (ppmhist can tell you), you can use pnmquant to reduce it to 256.

       If your input image is a PAM with transparency information, ppmtogif uses one entry in the
       GIF  colormap  specifically for the transparent pixels, so you can have at most 255 opaque
       colors.	In contrast, if you use the -transparent option, one of the colors from the input
       becomes transparent, so the limit is still 256.

       pamtogif was new in Netpbm 10.37 (December 2006).  In older Netpbm, use ppmtogif.

	      Produce an interlaced GIF file.

       -sort  Produce a GIF file with a color map sorted in a predictable order.

	      This  does  not produce the sorted color map which is part of the GIF format.  That
	      kind of sorted color map is one where the colors are sorted according to how impor-
	      tant they are, and the GIF header tells the viewer that it is sorted that way.  Its
	      purpose is to allow the viewer to use fewer colors than are in the color map if  it
	      is not capable of displaying all the colors.

	      What  this  option  produces  is	a color map sorted by red value, then green, then
	      blue.  That can be useful in analyzing GIF images, particularly those made with two
	      versions of the program, because it removes some of the variability.


	      Use  the	colors	found in the file mapfile to create the colormap in the GIF file,
	      instead of the colors from netpbmfile.  mapfile can be any PPM file; all that  mat-
	      ters  is	the colors in it.  If the colors in netpbmfile do not match those in map-
	      file, pamtogif matches them to a 'best match.' You can obtain a much better  result
	      by using pnmremap to change the colors in the input to those in the map file.

	      The mapfile file is not a palette file, just an image whose colors you want to use.
	      The order of colors in the GIF palette have nothing to do with where they appear in
	      the mapfile image, and duplication of colors in the image is irrelevant.

	      The  map file's depth must match the number of color components in the input (which
	      is not necessarily the same as the input's depth -- the input might have	an  alpha
	      plane  in  addition).   If  your map file does not, or it might not, run your input
	      through pnmremap using the same map file so that it does.

	      pamtogif marks the specified color as transparent in the GIF image.

	      If you don't specify -transparent, pamtogif does not  mark  any  color  transparent
	      (except as indicated by the transparency information in the input file).

	      Specify  the  color  (color)  as described for the argument of the ppm_parsecolor()
	      library routine <libppm.html#colorname> .

	      If the color you specify is not present in the image, pamtogif 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, pamtogif 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.  pamtogif issues an information
	      message when this is the case.

	      When you specify -transparent, pamtogif ignores explicit	transparency  information
	      (the 'alpha channel') in the input image.

	      There  is  no  -alpha option.  pamtogif's predecessor had such an option because it
	      was not capable of taking PAM input that contains a transparency (alpha) plane,  so
	      one used this option to supply a transparency plane as a separate PGM file.

	       This  option names a PGM file that contains an alpha mask for the image.  pamtogif
	      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, pamtogif 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.

	      This specifies the foreground color for transparent pixels.  A viewer may  use  the
	      foreground  color  for  a transparent pixel if it chooses not to have another color
	      'show through.'.	The default is black.

	      This applies only to pixels that are transparent in the GIF because they are trans-
	      parent  in  the Netpbm input.  If a GIF pixel is transparent because of the -trans-
	      parent option, the foreground color is the color indicated by that option.

	      Note that in GIF, all transparent pixels have the same foreground color.	(There is
	      only one entry in the GIF colormap for transparent pixels).

	      Specify  the  color  (color)  as described for the argument of the ppm_parsecolor()
	      library routine <libppm.html#colorname> .

	      Include a comment in the GIF output with comment text text.

	      Without this option, there are no comments in the output.

	      Note that in a command shell, you'll have to use quotation marks around text if  it
	      contains	characters  (e.g.  space)  that would make the shell think it is multiple
	      $ pamtogif -comment "this is a comment" <xxx.ppm >xxx.gif


	      This option is mainly of historical interest -- it involves use of a patent that is
	      now expired.

	      This  option  causes the GIF output, and thus pamtogif, not to use LZW (Lempel-Ziv)
	      compression.  As a result, the image file is larger and, before the patent expired,
	      no  royalties  would  be	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, pamtogif 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 pamtogif -nolzw , he is
	      then using the LZW patent.  But the patent holder expressed far  less  interest  in
	      enforcing the patent on decoding than on encoding.

	      This  is the aspect ratio of the pixels of the image.  Its only effect is to record
	      that information in the GIF for use by whatever interprets the GIF.  Note that this
	      feature  of  GIF	is hardly ever used and most GIF decoders ignore this information
	      and assume pixels are square.

	      Pixels in a Netpbm image do not have aspect ratios; there is always a one-one  cor-
	      respondence between GIF pixels and Netpbm pixels.

	      The  aspect  ratio  is  the quotient of width divided by height.	GIF allows aspect
	      ratios from 0.25 (1:4) to 4 (4:1) in increments of  1/64.   pamtogif  implements	a
	      natural extension of GIF that allows an aspect ratio up to 4 14/64.  If you specify
	      anything outside this range, pamtogif fails.  pamtogif rounds fraction to the near-
	      est 1/64.

	      The default is square (1.0).

	      This  option  was  new  in  Netpbm 10.38 (March 2007).  Before that, the pixels are
	      always square.

	      This option causes pamtogif to display information about the conversion process and
	      the image it produces.

       giftopnm(1) , pnmremap(1) , ppmtogif(1) ,

       gifsicle http://www.lcdf.org/gifsicle <http://www.lcdf.org/gifsicle> , pnm(1) , pam(1)

       pamtogif was new in Netpbm 10.37 (December 2006).  It replaced ppmtogif, which created GIF
       images for Pbmplus/Netpbm users since 1989.

       The main outward change in the conversion from ppmtogif to pamtogif was that pamtogif  was
       able  to  use  transparency  information ('alpha channel') in PAM input, whereas with ppm-
       togif, one had to supply the transparency mask in a separate  pseudo-PGM  image	(via  the
       -alpha option).

       Jef  Poskanzer  wrote  ppmtogif	in  1989,  and	it  has always been a cornerstone of Pbm-
       plus/Netpbm because GIF is such a popular image format.	Jef based  the	LZW  encoding  on
       GIFENCOD  by  David  Rowley  <mgardi@watdcsu.waterloo.edu>.   Jef included GIFENCOD's GIF-
       COMPR.C file pretty much whole.	Rowley, in turn, adapted the LZW  compression  code  from
       classic Unix compress, which used techniques described in IEEE Computer, June 1984.

       Jef's  ppmtogif	notably lacked the ability to use a transparency mask with it.	You could
       create transparent pixels in a GIF, but only with the -transparent option,  which  allowed
       one  to	specify  that  all pixels of a certain color in the input were to be transparent.
       Bryan Henderson added the -alpha option in July 2001 so you could supply a mask image that
       indicates exactly which pixels are to be transparent, and those pixels could have the same
       color as other opaque ones.

       Bryan Henderson added another significant piece of code and function in October 2001:  the
       ability	to  generate a GIF without using the LZW patent -- an uncompressed GIF.  This was
       very important to many people at the time because the GIF patent was still in  force,  and
       this allowed them to make an image that any GIF viewer could display, royalty-free.  Bryan
       adapted code from the Independent JPEG Group's djpeg for that.

       There is no code in pamtogif from Jef's original, but Jef may still hold copyright over it
       due  to the way in which it evolved.  Virtually all of the code in pamtogif was written by
       Bryan Henderson and contributed to the public domain.

       If you use pamtogif without the -nolzw option, you are using a patent on the LZW  compres-
       sion  method  which  is owned by Unisys.  The patent has expired (in 2003 in the US and in
       2004 elsewhere), so it doesn't matter.  While the patent was in	force,	most  people  who
       used  pamtogif and similar programs did so without a license from Unisys to do so.  Unisys
       typically asked $5000 for a license for trivial use of the patent.  Unisys never  enforced
       the patent against trivial users.

       Rumor has it that IBM also owns or owned a patent covering pamtogif.

       A replacement for the GIF format that never required any patents to use is the PNG format.

netpbm documentation			  22 March 2007 		  Pamtogif User Manual(0)
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