giftopnm



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}] [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
              Only output GIF89 comment fields.


       -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.

              The  all  value  was added in Netpbm 10.16 (June 2003).  Earlier
              giftopnm can extract only one image.





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

       ppmtogif(1), ppmcolormask(1), pamcomp(1),  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             16 June 2003          Giftopnm User Manual(0)

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