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]
12
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).
21
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.
29
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       --alphaout=alpha-filename
43              giftopnm   creates a PBM file containing the transparency infor‐
44              mation from the input image.  This  transparency  image  is  the
45              same dimensions as the input image, and each pixel of the trans‐
46              parency image tells whether the corresponding pixel of the input
47              image  is  transparent.   Black  means  transparent; white means
48              opaque.  If you don't specify --alphaout, giftopnm does not gen‐
49              erate  a  transparency file, and if the input image has a trans‐
50              parency channel, giftopnm simply discards it.
51
52              If you specify - as the filename,  giftopnm  writes  the  trans‐
53              parency output to Standard Output and discards the image.
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55              See pamcomp(1) for one way to use the transparency output file.
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58       -verbose
59              Produce verbose output about the GIF file input.
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62       -comments
63              With  this option, giftopnm issues messages showing the GIF com‐
64              ments (A GIF89 stream can contain  comments  in  comment  exten‐
65              sions).
66
67              By default, giftopnm ignores comment extensions.
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71       -image={N,all}
72              This option identifies which image from the GIF stream you want.
73              You can select either one image or all the images.   Select  all
74              the  images  with  all.   Select  one  image  by  specifying its
75              sequence number in the stream: 1, 2, 3, etc.
76
77              The default is just Image 1.
78
79              A GIF stream normally contains only one image, so you don't need
80              this  option.   But  some streams, including animated GIFs, have
81              multiple images.
82
83              When you select multiple GIF images, the output is a PNM  stream
84              with multiple images.
85
86              If  you specify a single image, giftopnm must read and partially
87              validate the images before that in the stream.  It  may  or  may
88              not do the same for the images after it; see -quitearly.
89
90              The  all  value  was added in Netpbm 10.16 (June 2003).  Earlier
91              giftopnm can extract only one image.
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94       -repair
95              This option makes giftopnm try to salvage what it  can  from  an
96              invalid GIF input.
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98              In  particular,  when  giftopnm  detects  that  the GIF input is
99              invalid so that it is impossible to determine  what  the  pixels
100              are intended to be, it produces a single arbitrary color for all
101              further pixels in the image.  giftopnm processes the image  from
102              top  to bottom, left to right, so this means the bottommost pix‐
103              els will be this padding.
104
105              giftopnm issues warning messages when it salvages  an  image  in
106              this way.
107
108              Without  this option, giftopnm fails when it detects invalid GIF
109              input.  Any output it produces is arbitrary,  and  typically  is
110              not a valid PNM image.
111
112              It  is  fairly  common for an image to be corrupted such that is
113              started off as a valid GIF, but had the end of the file cut off.
114              An interrupted network transfer tends to do this.  In this case,
115              giftopnm's salvage operation will produce a valid PNM  image  of
116              the proper dimensions, but with a single arbitrary color for the
117              pixels that were left out of the file.
118
119              This option was new in Netpbm 10.38 (March  2007).   From  10.32
120              through  10.37,  giftopnm always fails if it detects invalid GIF
121              input.  Before 10.32, it succeeds in the  case  of  a  truncated
122              image,  and  replaces  the missing pixels with arbitrary colors,
123              not necessarily all the  same  (The  pre-10.32  behavior  wasn't
124              actually intended by the design).
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127
128       -quitearly
129              This  option  makes giftopnm stop reading its input file as soon
130              as it has converted and output the images from  the  input  that
131              you  requested.  By default, giftopnm reads until the end of the
132              GIF stream, ignoring any data after the images you requested.
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134              Two reasons not to use this option:
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136
137       ·      The input file is a pipe and the process that  is  filling  that
138              pipe expects the pipe to take the entire stream and will fail or
139              get stuck if it doesn't.
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141
142       ·      You want to validate the entire GIF stream.
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145
146              Two reasons to use this option:
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150       ·      It saves the time and other resources to read  the  end  of  the
151              stream.
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153       ·      There  are  errors  in  the end of the stream that make giftopnm
154              fail.
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156
157              This option has no effect if you also specify -image=all
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159              This option was new in Netpbm 10.35 (August 2006).  Before that,
160              giftopnm always reads the entire stream.
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RESTRICTIONS

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

171       pamtogif(1), ppmcolormask(1), pamcomp(1),  http://www.lcdf.org/gifsicle
172http://www.lcdf.org/gifsicle⟩ , ppm(1).
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AUTHOR

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

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

195       This  manual  page was generated by the Netpbm tool 'makeman' from HTML
196       source.  The master documentation is at
197
198              http://netpbm.sourceforge.net/doc/giftopnm.html
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200netpbm documentation           13 September 2012       Giftopnm User Manual(0)
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