man > giftopnm(1)

Giftopnm User Manual(1)                General Commands Manual               Giftopnm User Manual(1)

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 sep‐
       arate 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  con‐
       tains 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 oth‐
       erwise,  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 ]8;;index.html#commonoptions\ Common Options]8;;\ ), 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 im‐
              age  is transparent.  Black means transparent; white means opaque.  If you don't spec‐
              ify --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  ei‐
              ther  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 im‐
              possible to determine what the pixels are intended to be, it produces a  single  arbi‐
              trary  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  nec‐
              essarily 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), ]8;;http://www.lcdf.org/gifsicle\http://www.lcdf.org/gifsicle]8;;\ , ppm(1).


AUTHOR
       Copyright (c) 1993 by David Koblas (koblas AT 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

netpbm documentation                      13 September 2012                  Giftopnm User Manual(1)