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 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 output.

OPTIONS

       In addition to the options common to all programs based on libnetpbm (most notably -quiet, see
        Common Options ⟨index.html#commonoptions⟩ ), giftopnm recognizes the following command line options:

       --alphaout=alpha-filename
              giftopnm   creates  a PBM file containing the transparency information from the input image.  This
              transparency image is the same dimensions as the input image, and each pixel of  the  transparency
              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  a
              transparency file, and if the input image has a transparency channel, giftopnm simply discards it.

              If  you  specify - as the filename, giftopnm writes the transparency output to Standard Output and
              discards the image.

              See pamcomp(1) for one way to use the transparency 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 all 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 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 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.

DOCUMENT SOURCE

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master  documentation
       is at

              http://netpbm.sourceforge.net/doc/giftopnm.html