giftopnm

   Updated: 16 June 2003
   Table Of Contents

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 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.

   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 on-
ly 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 pnmscale to correct the output.

OPTIONS

   --alphaout=alpha-filename
	  giftopnm creates a PGM (portable graymap) file contain-
ing 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
	  (transparent)	 alpha values. If you don't specify --al-
phaout, 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 for one way to use 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  con-
taining them.

SEE ALSO

   ppmtogif,  ppmcolormask,  pamcomp, , ppm.

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 de-
compression
   (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.
     _________________________________________________________________



Table Of Contents

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * RESTRICTIONS
     * SEE ALSO
     * AUTHOR
     * LICENSE

UNIX/Linux commands referenced on this page:

1. convert
2. file
3. more
4. pnmscale
5. as
6. pamcomp
7. which
8. ppmtogif
9. ppmcolormask
10. time
11. less