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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] [GIF-
       file]

       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 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 cor-
       rect the output.


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 contains all  zero  (trans-
              parent) 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 output 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 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 arbi-
              trary, 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 actu-
              ally 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 , ppm(1).


AUTHOR
       Copyright (c) 1993 by David Koblas (koblasATnetcom.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            11 August 2008         Giftopnm User Manual(0)