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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  dou‐
       ble  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 out‐
       put 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 happen).	The pixels of a Netpbm
       image are always square.	 Because of the engineering complexity	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  out‐
       put.

OPTIONS
       --alphaout=alpha-filename
	      giftopnm	 creates  a PGM (portable graymap) file containing the
	      alpha channel values in the input image.	 If  the  input	 image
	      doesn't  contain	an alpha channel, the alpha-filename file con‐
	      tains all zero (transparent) alpha values.  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 out‐
	      put to Standard Output and discards the image.

	      See pamcomp(1)foronewaytouse the alpha output file.

       -verbose
	      Produce verbose output about the GIF file input.

       -comments
	      With  this option, giftopnm issues messages showing the GIF com‐
	      ments (A GIF89 stream can contain	 comments  in  comment	exten‐
	      sions).

	      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 pix‐
	      els 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
	      pixels 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:

       ·      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.

       ·      You want to validate the entire GIF stream.

	      Two reasons to use this option:

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

       ·      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 compres‐
       sion.  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		11 August 2008	       Giftopnm User Manual(0)
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