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