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<HTML><HEAD><TITLE>Giftopnm User Manual</TITLE></HEAD>
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<BODY>
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giftopnm
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Updated: 13 September 2012
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Table Of Contents
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NAME
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giftopnm - convert a GIF file into a PNM image
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SYNOPSIS
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giftopnm
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[--alphaout={alpha-filename,-}]
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[-verbose]
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[-comments]
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[-image={N,all}]
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[-repair]
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[-quitearly]
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[GIFfile]
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Minimum unique abbreviation of option is acceptable.  You may use double
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hyphens instead of single hyphen to denote options.  You may use white
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space in place of the equals sign to separate an option name from its value.
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DESCRIPTION
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This program is part of Netpbm.
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This is a graphics format converter from the GIF format to the PNM
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(i.e. PBM, PGM, or PPM) format.
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If the image contains only black and maximally bright white, the
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output is PBM.  If the image contains more than those two colors, but
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only grays, the output is PGM.  If the image contains other colors,
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the output is PPM.
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 A GIF image contains rectangular pixels.  They all have the same
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aspect ratio, but may not be square (it's actually quite unusual for
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them not to be square, but it could happen).  The pixels of a Netpbm
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image are always square.  Because of the engineering complexity to do
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otherwise, giftopnm converts a GIF image to a Netpbm image
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pixel-for-pixel.  This means if the GIF pixels are not square, the
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Netpbm output image has the wrong aspect ratio.  In this case,
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giftopnm issues an informational message telling you to run
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pamscale to correct the output.
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OPTIONS
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--alphaout=alpha-filename
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giftopnm  creates a PBM file containing the transparency
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information from the input image.  This transparency image is the same
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dimensions as the input image, and each pixel of the transparency image tells
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whether the corresponding pixel of the input image is transparent.  Black
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means transparent; white means opaque.  If you don't
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specify --alphaout, giftopnm does not generate a transparency
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file, and if the input image has a transparency channel, giftopnm simply
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discards it.
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If you specify - as the filename, giftopnm writes the
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transparency output to Standard Output and discards the image.
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See pamcomp for one way to use
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the transparency output file.
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-verbose
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Produce verbose output about the GIF file input.
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-comments
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With this option, giftopnm issues messages showing the GIF comments
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(A GIF89 stream can contain comments in comment extensions).
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By default, giftopnm ignores comment extensions.
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-image={N,all}
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This option identifies which image from the GIF stream you want.
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You can select either one image or all the images.  Select all the
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images with all.  Select one image by specifying its sequence
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number in the stream: 1, 2, 3, etc.
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The default is just Image 1.
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A GIF stream normally contains only one image, so you don't need
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this option.  But some streams, including animated GIFs, have multiple
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images.
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When you select multiple GIF images, the output is a PNM stream with
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multiple images.
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If you specify a single image, giftopnm must read and
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partially validate the images before that in the stream.  It may or may
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not do the same for the images after it; see -quitearly.
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The all value was added in Netpbm 10.16 (June 2003).  Earlier
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giftopnm can extract only one image.
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-repair
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This option makes giftopnm try to salvage what it can from an
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invalid GIF input.
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In particular, when giftopnm detects that the GIF input is
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invalid so that it is impossible to determine what the pixels are
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intended to be, it produces a single arbitrary color for all further
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pixels in the image.  giftopnm processes the image from top to
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bottom, left to right, so this means the bottommost pixels will be
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this padding.
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giftopnm issues warning messages when it salvages an image
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in this way.
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Without this option, giftopnm fails when it detects invalid
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GIF input.  Any output it produces is arbitrary, and typically is not
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a valid PNM image.
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It is fairly common for an image to be corrupted such that is
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started off as a valid GIF, but had the end of the file cut off.  An
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interrupted network transfer tends to do this.  In this case,
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giftopnm's salvage operation will produce a valid PNM image of
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the proper dimensions, but with a single arbitrary color for the pixels
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that were left out of the file.
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This option was new in Netpbm 10.38 (March 2007).  From 10.32 through
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10.37, giftopnm always fails if it detects invalid GIF input.
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Before 10.32, it succeeds in the case of a truncated image, and replaces
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the missing pixels with arbitrary colors, not necessarily all the same
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(The pre-10.32 behavior wasn't actually intended by the design).
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-quitearly
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This option makes giftopnm stop reading its input file as soon
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as it has converted and output the images from the input that you requested.
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By default, giftopnm reads until the end of the GIF stream, ignoring
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any data after the images you requested.
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Two reasons not to use this option:
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  • The input file is a pipe and the process that is filling that pipe
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    expects the pipe to take the entire stream and will fail or get stuck
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    if it doesn't.
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  • You want to validate the entire GIF stream.
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    Two reasons to use this option:
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    • It saves the time and other resources to read the end of the stream.
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    • There are errors in the end of the stream that make giftopnm fail.
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      This option has no effect if you also specify -image=all
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      This option was new in Netpbm 10.35 (August 2006).  Before that,
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      giftopnm always reads the entire stream.
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      RESTRICTIONS
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      This does not correctly handle the Plain Text Extension of the
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      GIF89 standard, since I did not have any example input files
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      containing them.
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      SEE ALSO
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      pamtogif,
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      ppmcolormask,
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      pamcomp,
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      <
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      HREF="http://www.lcdf.org/gifsicle">http://www.lcdf.org/gifsicle>,
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      ppm.
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      AUTHOR
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      Copyright (c) 1993 by David Koblas (
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      HREF="mailto:koblas@netcom.com">koblas@netcom.com)
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      LICENSE
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      As a historical note, for a long time if you used giftopnm,
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      you were using a patent on the LZW compression method which was owned
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      by Unisys, and in all probability you did not have a license from
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      Unisys to do so.  Unisys typically asked $5000 for a license for
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      trivial use of the patent.  Unisys never enforced the patent against
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      trivial users, and made statements that it is much less concerned
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      about people using the patent for decompression (which is what
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      giftopnm does than for compression.  The patent expired in
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      2003.
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      Rumor has it that IBM also owns a patent covering giftopnm.
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      A replacement for the GIF format that has never required any patent
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      license to use is the PNG format.
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      Table Of Contents
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      • SYNOPSIS
        		•
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      • DESCRIPTION
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      • OPTIONS
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      • RESTRICTIONS
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      • SEE ALSO
        		•
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      • AUTHOR
        		•
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      • LICENSE
        		•
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