1Giftopnm User Manual(0)                                Giftopnm User Manual(0)
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NAME

6       giftopnm - convert a GIF file into a PNM image
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SYNOPSIS

10       giftopnm    [--alphaout={alpha-filename,-}]    [-verbose]   [-comments]
11       [-image={N,all}] [-repair] [-quitearly] [GIFfile]
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13       Minimum unique abbreviation of option is acceptable.  You may use  dou‐
14       ble  hyphens  instead  of single hyphen to denote options.  You may use
15       white space in place of the equals sign to separate an option name from
16       its value.
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DESCRIPTION

20       This program is part of Netpbm(1).
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22       This  is  a  graphics  format  converter from the GIF format to the PNM
23       (i.e. PBM, PGM, or PPM) format.
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25       If the image contains only black and maximally bright white, the output
26       is  PBM.   If  the  image contains more than those two colors, but only
27       grays, the output is PGM.  If the image contains other colors, the out‐
28       put is PPM.
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30        A  GIF  image  contains  rectangular  pixels.   They all have the same
31       aspect ratio, but may not be square (it's actually  quite  unusual  for
32       them  not  to  be square, but it could happen).  The pixels of a Netpbm
33       image are always square.  Because of the engineering complexity  to  do
34       otherwise,  giftopnm  converts a GIF image to a Netpbm image pixel-for-
35       pixel.  This means if the GIF pixels are not square, the Netpbm  output
36       image  has  the  wrong  aspect ratio.  In this case, giftopnm issues an
37       informational message telling you to run pamscale to correct  the  out‐
38       put.
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OPTIONS

42       In  addition  to  the options common to all programs based on libnetpbm
43       (most notably -quiet, see
44        Common Options ⟨index.html#commonoptions⟩ ), giftopnm  recognizes  the
45       following command line options:
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49       --alphaout=alpha-filename
50              giftopnm   creates a PBM file containing the transparency infor‐
51              mation from the input image.  This  transparency  image  is  the
52              same dimensions as the input image, and each pixel of the trans‐
53              parency image tells whether the corresponding pixel of the input
54              image  is  transparent.   Black  means  transparent; white means
55              opaque.  If you don't specify --alphaout, giftopnm does not gen‐
56              erate  a  transparency file, and if the input image has a trans‐
57              parency channel, giftopnm simply discards it.
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59              If you specify - as the filename,  giftopnm  writes  the  trans‐
60              parency output to Standard Output and discards the image.
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62              See pamcomp(1) for one way to use the transparency output file.
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65       -verbose
66              Produce verbose output about the GIF file input.
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69       -comments
70              With  this option, giftopnm issues messages showing the GIF com‐
71              ments (A GIF89 stream can contain  comments  in  comment  exten‐
72              sions).
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74              By default, giftopnm ignores comment extensions.
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78       -image={N,all}
79              This option identifies which image from the GIF stream you want.
80              You can select either one image or all the images.   Select  all
81              the  images  with  all.   Select  one  image  by  specifying its
82              sequence number in the stream: 1, 2, 3, etc.
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84              The default is just Image 1.
85
86              A GIF stream normally contains only one image, so you don't need
87              this  option.   But  some streams, including animated GIFs, have
88              multiple images.
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90              When you select multiple GIF images, the output is a PNM  stream
91              with multiple images.
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93              If  you specify a single image, giftopnm must read and partially
94              validate the images before that in the stream.  It  may  or  may
95              not do the same for the images after it; see -quitearly.
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97              The  all  value  was added in Netpbm 10.16 (June 2003).  Earlier
98              giftopnm can extract only one image.
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101       -repair
102              This option makes giftopnm try to salvage what it  can  from  an
103              invalid GIF input.
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105              In  particular,  when  giftopnm  detects  that  the GIF input is
106              invalid so that it is impossible to determine  what  the  pixels
107              are intended to be, it produces a single arbitrary color for all
108              further pixels in the image.  giftopnm processes the image  from
109              top  to bottom, left to right, so this means the bottommost pix‐
110              els will be this padding.
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112              giftopnm issues warning messages when it salvages  an  image  in
113              this way.
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115              Without  this option, giftopnm fails when it detects invalid GIF
116              input.  Any output it produces is arbitrary,  and  typically  is
117              not a valid PNM image.
118
119              It  is  fairly  common for an image to be corrupted such that is
120              started off as a valid GIF, but had the end of the file cut off.
121              An interrupted network transfer tends to do this.  In this case,
122              giftopnm's salvage operation will produce a valid PNM  image  of
123              the proper dimensions, but with a single arbitrary color for the
124              pixels that were left out of the file.
125
126              This option was new in Netpbm 10.38 (March  2007).   From  10.32
127              through  10.37,  giftopnm always fails if it detects invalid GIF
128              input.  Before 10.32, it succeeds in the  case  of  a  truncated
129              image,  and  replaces  the missing pixels with arbitrary colors,
130              not necessarily all the  same  (The  pre-10.32  behavior  wasn't
131              actually intended by the design).
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134
135       -quitearly
136              This  option  makes giftopnm stop reading its input file as soon
137              as it has converted and output the images from  the  input  that
138              you  requested.  By default, giftopnm reads until the end of the
139              GIF stream, ignoring any data after the images you requested.
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141              Two reasons not to use this option:
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144       ·      The input file is a pipe and the process that  is  filling  that
145              pipe expects the pipe to take the entire stream and will fail or
146              get stuck if it doesn't.
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149       ·      You want to validate the entire GIF stream.
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153              Two reasons to use this option:
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157       ·      It saves the time and other resources to read  the  end  of  the
158              stream.
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160       ·      There  are  errors  in  the end of the stream that make giftopnm
161              fail.
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163
164              This option has no effect if you also specify -image=all
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166              This option was new in Netpbm 10.35 (August 2006).  Before that,
167              giftopnm always reads the entire stream.
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RESTRICTIONS

173       This  does  not  correctly handle the Plain Text Extension of the GIF89
174       standard, since I did not have any example input files containing them.
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SEE ALSO

178       pamtogif(1), ppmcolormask(1), pamcomp(1),  http://www.lcdf.org/gifsicle
179http://www.lcdf.org/gifsicle⟩ , ppm(1).
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AUTHOR

183       Copyright (c) 1993 by David Koblas (koblas@netcom.com)
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LICENSE

187       As  a  historical  note, for a long time if you used giftopnm, you were
188       using a patent on the LZW compression method which was owned by Unisys,
189       and in all probability you did not have a license from Unisys to do so.
190       Unisys typically asked $5000 for a  license  for  trivial  use  of  the
191       patent.   Unisys  never  enforced the patent against trivial users, and
192       made statements that it is much less concerned about people  using  the
193       patent for decompression (which is what giftopnm does than for compres‐
194       sion.  The patent expired in 2003.
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196       Rumor has it that IBM also owns a patent covering giftopnm.
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198       A replacement for the GIF format that has  never  required  any  patent
199       license to use is the PNG format.
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DOCUMENT SOURCE

202       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
203       source.  The master documentation is at
204
205              http://netpbm.sourceforge.net/doc/giftopnm.html
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207netpbm documentation           13 September 2012       Giftopnm User Manual(0)
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