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Giftopnm User Manual(0) 						  Giftopnm User Manual(0)

NAME
       giftopnm - convert a GIF file into a PNM image

SYNOPSIS
       giftopnm [--alphaout={alpha-filename,-}] [-verbose] [-comments] [-image={N,all}] [-repair]
       [-quitearly] [GIFfile]

       Minimum unique abbreviation of option is acceptable.  You may use double  hyphens  instead
       of  single  hyphen to denote options.  You may use white space in place of the equals sign
       to separate an option name from its value.

DESCRIPTION
       This program is part of Netpbm(1)

       This is a graphics format converter from the GIF format to the PNM (i.e. PBM, PGM, or PPM)
       format.

       If  the	image  contains only black and maximally bright white, the output is PBM.  If the
       image contains more than those two colors, but only grays, the  output  is  PGM.   If  the
       image contains other colors, the output is PPM.

	A  GIF	image  contains rectangular pixels.  They all have the same aspect ratio, but may
       not be square (it's actually quite unusual for them not to be square, but  it  could  hap-
       pen).   The  pixels  of a Netpbm image are always square.  Because of the engineering com-
       plexity to do otherwise, giftopnm converts a GIF image to a Netpbm image  pixel-for-pixel.
       This  means if the GIF pixels are not square, the Netpbm output image has the wrong aspect
       ratio.  In this case, giftopnm issues an informational message telling you to run pamscale
       to correct the output.

OPTIONS
       --alphaout=alpha-filename
	      giftopnm	creates a PBM file containing the transparency information from the input
	      image.  This 'alpha image' is the same dimensions as  the  input	image,	and  each
	      pixel  of  the alpha image tells whether the corresponding pixel of the input image
	      is transparent.  Black means transparent; white means opaque.  If you don't specify
	      --alphaout, giftopnm does not generate an alpha file, and if the input image has an
	      alpha channel, giftopnm simply discards it.

	      If you specify - as the filename, giftopnm writes the alpha output to Standard Out-
	      put and discards the image.

	      See pamcomp(1)
	       for one way to use the alpha output file.

       -verbose
	      Produce verbose output about the GIF file input.

       -comments
	      With this option, giftopnm issues messages showing the GIF comments (A GIF89 stream
	      can contain comments in comment extensions).

	      By default, giftopnm ignores comment extensions.

       -image={N,all}
	      This option identifies which image from the GIF stream you want.	 You  can  select
	      either  one  image  or  all the images.  Select al the images with all.  Select one
	      image by specifying its sequence number in the stream: 1, 2, 3, etc.

	      The default is just Image 1.

	      A GIF stream normally contains only one image, so you don't need this option.   But
	      some streams, including animated GIFs, have multiple images.

	      When  you  select  multiple  GIF	images,  the output is a PNM stream with multiple
	      images.

	      If you specify a single image, giftopnm must read and partially validate the images
	      before  that in the stream.  It may or may not do the same for the images after it;
	      see -quitearly.

	      The all value was added in Netpbm 10.16 (June 2003).  Earlier giftopnm can  extract
	      only one image.

       -repair
	      This option makes giftopnm try to salvage what it can from an invalid GIF input.

	      In  particular,  when  giftopnm detects that the GIF input is invalid so that it is
	      impossible to determine what the pixels are intended to be, it  produces	a  single
	      arbitrary  color for all further pixels in the image.  giftopnm processes the image
	      from top to bottom, left to right, so this means the bottommost pixels will be this
	      padding.

	      giftopnm issues warning messages when it salvages an image in this way.

	      Without  this option, giftopnm fails when it detects invalid GIF input.  Any output
	      it produces is arbitrary, and typically is not a valid PNM image.

	      It is fairly common for an image to be corrupted such that  is  started  off  as	a
	      valid  GIF,  but	had the end of the file cut off.  An interrupted network transfer
	      tends to do this.  In this case, giftopnm's salvage operation will produce a  valid
	      PNM  image of the proper dimensions, but with a single arbitrary color for the pix-
	      els that were left out of the file.

	      This option was new in Netpbm  10.38  (March  2007).   From  10.32  through  10.37,
	      giftopnm	always	fails if it detects invalid GIF input.	Before 10.32, it succeeds
	      in the case of a truncated image, and replaces the missing  pixels  with	arbitrary
	      colors,  not  necessarily  all  the  same  (The  pre-10.32 behavior wasn't actually
	      intended by the design).

       -quitearly
	      This option makes giftopnm stop reading its input file as soon as it has	converted
	      and  output  the	images	from  the input that you requested.  By default, giftopnm
	      reads until the end of the GIF stream, ignoring  any  data  after  the  images  you
	      requested.

	      Two reasons not to use this option:

       o      The input file is a pipe and the process that is filling that pipe expects the pipe
	      to take the entire stream and will fail or get stuck if it doesn't.

       o      You want to validate the entire GIF stream.

	      Two reasons to use this option:

       o      It saves the time and other resources to read the end of the stream.

       o      There are errors in the end of the stream that make giftopnm fail.

	      This option has no effect if you also specify -image=all

	      This option was new in Netpbm 10.35 (August 2006).  Before  that,  giftopnm  always
	      reads the entire stream.

RESTRICTIONS
       This does not correctly handle the Plain Text Extension of the GIF89 standard, since I did
       not have any example input files containing them.

SEE ALSO
       pamtogif(1)   ,	  ppmcolormask(1)    ,	  pamcomp(1)	,    http://www.lcdf.org/gifsicle
       <http://www.lcdf.org/gifsicle> , ppm(1)

AUTHOR
       Copyright (c) 1993 by David Koblas (koblas@netcom.com)

LICENSE
       As a historical note, for a long time if you used giftopnm, you were using a patent on the
       LZW compression method which was owned by Unisys, and in all probability you did not  have
       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,	and  made
       statements  that it is much less concerned about people using the patent for decompression
       (which is what giftopnm does than for compression.  The patent expired in 2003.

       Rumor has it that IBM also owns a patent covering giftopnm.

       A replacement for the GIF format that has never required any patent license to use is  the
       PNG format.

netpbm documentation			13 September 2012		  Giftopnm User Manual(0)
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