1Pamtogif User Manual(0) Pamtogif User Manual(0)
2
6 pamtogif - convert a Netpbm image to a GIF image
7
10 pamtogif
11 [-interlace]
13 [-sort]
15 [-mapfile=mapfile] [-transparent=[=]color]
17 [-alphacolor=color]
19 [-comment=text]
21 [-nolzw]
23 [-aspect=fraction]
25 [-verbose] [netpbmfile]
27 All options can be abbreviated to their shortest unique prefix. You
29 may use two hyphens instead of one to designate an option. You may use
30 either white space or an equals sign between an option name and its
31 value.
32
35 This program is part of Netpbm(1).
36 pamtogif reads a Netpbm image as input and produces a GIF file as out‐
38 put.
39 This program creates only individual GIF images. To combine multiple
41 GIF images into an animated GIF, use gifsicle
42 ⟨http://www.lcdf.org/gifsicle/⟩ (not part of the Netpbm package).
43 pamtogif creates either an original GIF87 format GIF file or the newer
45 GIF89 format. It creates GIF89 when you request features that were new
46 with GIF89, to wit the -transparent or -comment options. Otherwise, it
47 creates GIF87. Really old GIF readers conceivably could not recognize
48 GIF89.
49 The GIF format is not capable of representing an image with more than
51 256 colors in it (it contains a color map with a maximum size of 256).
52 If the image you want to convert has more colors than that (ppmhist can
53 tell you), you can use pnmquant to reduce it to 256. Or use the more
54 complex but faster method described under the -mapfile option.
55 If your input image is a PAM with transparency information, ppmtogif
57 uses one entry in the GIF colormap specifically for the transparent
58 pixels, so you can have at most 255 opaque colors. In contrast, if you
59 use the -transparent option, one of the colors from the input becomes
60 transparent, so the limit is still 256.
61 pamtogif was new in Netpbm 10.37 (December 2006). In older Netpbm, use
63 ppmtogif.
64
67 -interlace
68 Produce an interlaced GIF file.
69 -sort Produce a GIF file with a color map sorted in a predictable
72 order.
73 This does not produce the sorted color map which is part of the
75 GIF format. That kind of sorted color map is one where the col‐
76 ors are sorted according to how important they are, and the GIF
77 header tells the viewer that it is sorted that way. Its purpose
78 is to allow the viewer to use fewer colors than are in the color
79 map if it is not capable of displaying all the colors.
80 What this option produces is a color map sorted by red value,
82 then green, then blue. That can be useful in analyzing GIF
83 images, particularly those made with two versions of the pro‐
84 gram, because it removes some of the variability.
85 -mapfile=mapfile
89 Use the colors found in the file mapfile to create the colormap
91 in the GIF file, instead of the colors from netpbmfile. mapfile
92 can be any PPM file; all that matters is the colors in it. If
93 the colors in netpbmfile do not match those in mapfile, pamtogif
94 matches them to a "best match." You can obtain a much better
95 result by using pnmremap to change the colors in the input to
96 those in the map file.
97 The mapfile file is not a palette file, just an image whose col‐
99 ors you want to use. The order of colors in the GIF palette
100 have nothing to do with where they appear in the mapfile image,
101 and duplication of colors in the image is irrelevant.
102 The map file's depth must match the number of color components
104 in the input (which is not necessarily the same as the input's
105 depth -- the input might have a transparency plane in addition).
106 If your map file does not, or it might not, run your input
107 through pnmremap using the same map file so that it does.
108 You can use -mapfile to speed up conversion of an image where
110 you already have a map file because of earlier processing of
111 your image. For example, it is common to start with an image
112 that has more than 256 colors and remap its colors to a set of
113 256 colors so that pamgtogif can convert it (a GIF can have only
114 256 colors; pamtogif without -mapfile fails on any image that
115 has more than that) with pnmquant. When you do this, pnmquant
116 generates a palette to do the color quantization, then pamtogif
117 generates an identical palette from the quantized image. You
118 can save computation by generating the palette once:
119 $ pnmcolormap 256 myimage.ppm >/tmp/colormap.ppm
121 $ pamtogif myimage.ppm -mapfile=/tmp/colormap.ppm >output.gif
122 -transparent=color
126 pamtogif marks the specified color as transparent in the GIF
127 image.
128 If you don't specify -transparent, pamtogif does not mark any
130 color transparent (except as indicated by the transparency
131 information in the input file).
132 Specify the color (color) as described for the argument of the
134 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ .
135 If the color you specify is not present in the image, pamtogif
137 selects instead the color in the image that is closest to the
138 one you specify. Closeness is measured as a Cartesian distance
139 between colors in RGB space. If multiple colors are equidis‐
140 tant, pamtogif chooses one of them arbitrarily.
141 However, if you prefix your color specification with "=", e.g.
143 -transparent==red, only the exact color you specify will be
144 transparent. If that color does not appear in the image, there
145 will be no transparency. pamtogif issues an information message
146 when this is the case.
147 When you specify -transparent, pamtogif ignores explicit trans‐
149 parency information (the "alpha channel") in the input image.
150 -alpha=pgmfile
153 There is no -alpha option. pamtogif's predecessor had such an
154 option because it was not capable of taking PAM input that con‐
155 tains a transparency (alpha) plane, so one used this option to
156 supply a transparency plane as a separate PGM file.
157 This option names a PGM file that contains a transparency mask
159 for the image. pamtogif creates fully transparent pixels wher‐
160 ever the transparency mask indicates transparency greater than
161 50%. The color of those pixels is that specified by the -alpha‐
162 color option, or black by default.
163 To do this, pamtogif creates an entry in the GIF colormap in
165 addition to the entries for colors that are actually in the
166 image. It marks that colormap entry as transparent and uses
167 that colormap index in the output image to create a transparent
168 pixel.
169 The transparency image must be the same dimensions as the input
171 image, but may have any maxval. White means opaque and black
172 means transparent.
173 You cannot specify both -transparent and -alpha.
175 -alphacolor=color
178 This specifies the foreground color for transparent pixels. A
179 viewer may use the foreground color for a transparent pixel if
180 it chooses not to have another color "show through.". The
181 default is black.
182 This applies only to pixels that are transparent in the GIF
184 because they are transparent in the Netpbm input. If a GIF
185 pixel is transparent because of the -transparent option, the
186 foreground color is the color indicated by that option.
187 Note that in GIF, all transparent pixels have the same fore‐
189 ground color. (There is only one entry in the GIF colormap for
190 transparent pixels).
191 Specify the color (color) as described for the argument of the
193 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ .
194 -comment=text
197 Include a comment in the GIF output with comment text text.
198 Without this option, there are no comments in the output.
200 Note that in a command shell, you'll have to use quotation marks
202 around text if it contains characters (e.g. space) that would
203 make the shell think it is multiple arguments:
204 $ pamtogif -comment "this is a comment" <xxx.ppm >xxx.gif
205 -nolzw
208 This option is mainly of historical interest -- it involves use
210 of a patent that is now expired.
211 This option causes the GIF output, and thus pamtogif, not to use
213 LZW (Lempel-Ziv) compression. As a result, the image file is
214 larger and, before the patent expired, no royalties would be
215 owed to the holder of the patent on LZW. See the section
216 LICENSE below.
217 LZW is a method for combining the information from multiple pix‐
219 els into a single GIF code. With the -nolzw option, pamtogif
220 creates one GIF code per pixel, so it is not doing any compres‐
221 sion and not using LZW. However, any GIF decoder, whether it
222 uses an LZW decompressor or not, will correctly decode this
223 uncompressed format. An LZW decompressor would see this as a
224 particular case of LZW compression.
225 Note that if someone uses an LZW decompressor such as the one in
227 giftopnm or pretty much any graphics display program to process
228 the output of pamtogif -nolzw , he is then using the LZW patent.
229 But the patent holder expressed far less interest in enforcing
230 the patent on decoding than on encoding.
231 -aspect=fraction
234 This is the aspect ratio of the pixels of the image. Its only
235 effect is to record that information in the GIF for use by what‐
236 ever interprets the GIF. Note that this feature of GIF is
237 hardly ever used and most GIF decoders ignore this information
238 and assume pixels are square.
239 Pixels in a Netpbm image do not have aspect ratios; there is
241 always a one-one correspondence between GIF pixels and Netpbm
242 pixels.
243 The aspect ratio is the quotient of width divided by height.
245 GIF allows aspect ratios from 0.25 (1:4) to 4 (4:1) in incre‐
246 ments of 1/64. pamtogif implements a natural extension of GIF
247 that allows an aspect ratio up to 4 14/64. If you specify any‐
248 thing outside this range, pamtogif fails. pamtogif rounds frac‐
249 tion to the nearest 1/64.
250 The default is square (1.0).
252 This option was new in Netpbm 10.38 (March 2007). Before that,
254 the pixels are always square.
255 -verbose
259 This option causes pamtogif to display information about the
260 conversion process and the image it produces.
261
266 giftopnm(1), pnmremap(1), ppmtogif(1),
267 gifsicle http://www.lcdf.org/gifsicle ⟨http://www.lcdf.org/gifsicle⟩ ,
269 pnm(1), pam(1).
270
273 pamtogif was new in Netpbm 10.37 (December 2006). It replaced ppm‐
274 togif, which created GIF images for Pbmplus/Netpbm users since 1989.
275 The main outward change in the conversion from ppmtogif to pamtogif was
277 that pamtogif was able to use transparency information ("alpha chan‐
278 nel") in PAM input, whereas with ppmtogif, one had to supply the trans‐
279 parency mask in a separate pseudo-PGM image (via the -alpha option).
280 Jef Poskanzer wrote ppmtogif in 1989, and it has always been a corner‐
282 stone of Pbmplus/Netpbm because GIF is such a popular image format.
283 Jef based the LZW encoding on GIFENCOD by David Rowley <mgardi@watd‐
284 csu.waterloo.edu>. Jef included GIFENCOD's GIFCOMPR.C file pretty much
285 whole. Rowley, in turn, adapted the LZW compression code from classic
286 Unix compress, which used techniques described in IEEE Computer, June
287 1984.
288 Jef's ppmtogif notably lacked the ability to use a transparency mask
290 with it. You could create transparent pixels in a GIF, but only with
291 the -transparent option, which allowed one to specify that all pixels
292 of a certain color in the input were to be transparent. Bryan Hender‐
293 son added the -alpha option in July 2001 so you could supply a mask
294 image that indicates exactly which pixels are to be transparent, and
295 those pixels could have the same color as other opaque ones.
296 Bryan Henderson added another significant piece of code and function in
298 October 2001: the ability to generate a GIF without using the LZW
299 patent -- an uncompressed GIF. This was very important to many people
300 at the time because the GIF patent was still in force, and this allowed
301 them to make an image that any GIF viewer could display, royalty-free.
302 Bryan adapted code from the Independent JPEG Group's djpeg for that.
303 There is no code in pamtogif from Jef's original, but Jef may still
305 hold copyright over it because of the way in which it evolved. Virtu‐
306 ally all of the code in pamtogif was written by Bryan Henderson and
307 contributed to the public domain.
308
312 If you use pamtogif without the -nolzw option, you are using a patent
313 on the LZW compression method which is owned by Unisys. The patent has
314 expired (in 2003 in the US and in 2004 elsewhere), so it doesn't mat‐
315 ter. While the patent was in force, most people who used pamtogif and
316 similar programs did so without a license from Unisys to do so. Unisys
317 typically asked $5000 for a license for trivial use of the patent.
318 Unisys never enforced the patent against trivial users.
319 Rumor has it that IBM also owns or owned a patent covering pamtogif.
321 A replacement for the GIF format that never required any patents to use
323 is the PNG format.
324
326 This manual page was generated by the Netpbm tool 'makeman' from HTML
327 source. The master documentation is at
328 http://netpbm.sourceforge.net/doc/pamtogif.html
330netpbm documentation 22 March 2007 Pamtogif User Manual(0)