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1 perry 1 ppm
2 !!!ppm
3 NAME
4 DESCRIPTION
5 COMPATIBILITY
6 SEE ALSO
7 AUTHOR
8 ----
9 !!NAME
10
11
12 ppm - portable pixmap file format
13 !!DESCRIPTION
14
15
16 The portable pixmap format is a lowest common denominator
17 color image file format.
18
19
20 It should be noted that this format is egregiously
21 inefficient. It is highly redundant, while containing a lot
22 of information that the human eye can't even discern.
23 Furthermore, the format allows very little information about
24 the image besides basic color, which means you may have to
25 couple a file in this format with other independent
26 information to get any decent use out of it. However, it is
27 very easy to write and analyze programs to process this
28 format, and that is the point.
29
30
31 It should also be noted that files often conform to this
32 format in every respect except the precise semantics of the
33 sample values. These files are useful because of the way PPM
34 is used as an intermediary format. They are informally
35 called PPM files, but to be absolutely precise, you should
36 indicate the variation from true PPM. For example,
37
38
39 The format definition is as follows.
40
41
42 A PPM file consists of a sequence of one or more PPM images.
43 There are no data, delimiters, or padding before, after, or
44 between images.
45
46
47 Each PPM image consists of the following:
48
49
50 -
51
52
53 A
54
55
56 -
57
58
59 Whitespace (blanks, TABs, CRs, LFs).
60
61
62 -
63
64
65 A width, formatted as ASCII characters in
66 decimal.
67
68
69 -
70
71
72 Whitespace.
73
74
75 -
76
77
78 A height, again in ASCII decimal.
79
80
81 -
82
83
84 Whitespace.
85
86
87 -
88
89
90 The maximum color value (Maxval), again in ASCII decimal.
91 Must be less than 65536.
92
93
94 -
95
96
97 Newline or other single whitespace character.
98
99
100 -
101
102
103 A raster of Width * Height pixels, proceeding through the
104 image in normal English reading order. Each pixel is a
105 triplet of red, green, and blue samples, in that order. Each
106 sample is represented in pure binary by either 1 or 2 bytes.
107 If the Maxval is less than 256, it is 1 byte. Otherwise, it
108 is 2 bytes. The most significant byte is first.
109
110
111 -
112
113
114 In the raster, the sample values are
115
116
117 -
118
119
120 Note that a common variation on the PPM format is to have
121 the sample values be
122 pnmgamma__
123 takes such a PPM variant as input and produces a true PPM as
124 output.
125
126
127 -
128
129
130 Characters from a
131
132
133 Note that you can use __pnmdepth__ to convert between a
134 the format with 1 byte per sample and the one with 2 bytes
135 per sample.
136
137
138 There is actually another version of the PPM format that is
139 fairly rare:
140 pbm__(5) for some
141 commentary on how plain and raw formats relate to one
142 another.
143
144
145 The difference in the plain format is:
146
147
148 -
149
150
151 There is exactly one image in a file.
152
153
154 -
155
156
157 The magic number is P3 instead of P6.
158
159
160 -
161
162
163 Each sample in the raster is represented as an ASCII decimal
164 number (of arbitrary size).
165
166
167 -
168
169
170 Each sample in the raster has white space before and after
171 it. There must be at least one character of white space
172 between any two samples, but there is no maximum. There is
173 no particular separation of one pixel from another -- just
174 the required separation between the blue sample of one pixel
175 from the red sample of the next pixel.
176
177
178 -
179
180
181 No line should be longer than 70 characters.
182
183
184 Here is an example of a small pixmap in this
185 format:
186
187
188 P3
189 # feep.ppm
190 4 4
191 15
192 0 0 0 0 0 0 0 0 0 15 0 15
193 0 0 0 0 15 7 0 0 0 0 0 0
194 0 0 0 0 0 0 0 15 7 0 0 0
195 15 0 15 0 0 0 0 0 0 0 0 0
196 Programs that read this format should be as lenient as possible, accepting anything that looks remotely like a pixmap.
197 !!COMPATIBILITY
198
199
200 Before April 2000, a raw format PPM file could not have a
201 maxval greater than 255. Hence, it could not have more than
202 one byte per sample. Old programs may depend on
203 this.
204
205
206 Before July 2000, there could be at most one image in a PPM
207 file. As a result, most tools to process PPM files ignore
208 (and don't read) any data after the first
209 image.
210 !!SEE ALSO
211
212
213 giftopnm(1), gouldtoppm(1), ilbmtoppm(1), imgtoppm(1),
214 mtvtoppm(1), pcxtoppm(1), pgmtoppm(1), pi1toppm(1),
215 picttoppm(1), pjtoppm(1), qrttoppm(1), rawtoppm(1),
216 rgb3toppm(1), sldtoppm(1), spctoppm(1), sputoppm(1),
217 tgatoppm(1), ximtoppm(1), xpmtoppm(1), yuvtoppm(1),
218 ppmtoacad(1), ppmtogif(1), ppmtoicr(1), ppmtoilbm(1),
219 ppmtopcx(1), ppmtopgm(1), ppmtopi1(1), ppmtopict(1),
220 ppmtopj(1), ppmtopuzz(1), ppmtorgb3(1), ppmtosixel(1),
221 ppmtotga(1), ppmtouil(1), ppmtoxpm(1), ppmtoyuv(1),
222 ppmdither(1), ppmforge(1), ppmhist(1), ppmmake(1),
223 ppmpat(1), ppmquant(1), ppmquantall(1), ppmrelief(1),
224 pnm(5), pgm(5), pbm(5), 411toppm(1)
225 !!AUTHOR
226
227
228 Copyright (C) 1989, 1991 by Jef Poskanzer.
229 ----
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