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Annotated edit history of pgm(5) version 1, including all changes. View license author blame.
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1 perry 1 pgm
2 !!!pgm
3 NAME
4 DESCRIPTION
5 COMPATIBILITY
6 SEE ALSO
7 AUTHOR
8 ----
9 !!NAME
10
11
12 pgm - portable graymap file format
13 !!DESCRIPTION
14
15
16 The portable graymap format is a lowest common denominator
17 grayscale file format.
18
19
20 The format definition is as follows.
21
22
23 A PGM file consists of a sequence of one or more PGM images.
24 There are no data, delimiters, or padding before, after, or
25 between images.
26
27
28 Each PGM image consists of the following:
29
30
31 -
32
33
34 A
35
36
37 -
38
39
40 Whitespace (blanks, TABs, CRs, LFs).
41
42
43 -
44
45
46 A width, formatted as ASCII characters in
47 decimal.
48
49
50 -
51
52
53 Whitespace.
54
55
56 -
57
58
59 A height, again in ASCII decimal.
60
61
62 -
63
64
65 Whitespace.
66
67
68 -
69
70
71 The maximum gray value (Maxval), again in ASCII decimal.
72 Must be less than 65536.
73
74
75 -
76
77
78 Newline or other single whitespace character.
79
80
81 -
82
83
84 A raster of Width * Height gray values, proceeding through
85 the image in normal English reading order. Each gray value
86 is a number from 0 through Maxval, with 0 being black and
87 Maxval being white. Each gray value is represented in pure
88 binary by either 1 or 2 bytes. If the Maxval is less than
89 256, it is 1 byte. Otherwise, it is 2 bytes. The most
90 significant byte is first.
91
92
93 -
94
95
96 Each gray value is a number proportional to the intensity of
97 the pixel, adjusted by the CIE Rec. 709 gamma transfer
98 function. (That transfer function specifies a gamma number
99 of 2.2 and has a linear section for small intensities). A
100 value of zero is therefore black. A value of Maxval
101 represents CIE D65 white and the most intense value in the
102 image and any other image to which the image might be
103 compared.
104
105
106 -
107
108
109 Note that a common variation on the PGM format is to have
110 the gray value be
111 pnmgamma__
112 takes such a PGM variant as input and produces a true PGM as
113 output.
114
115
116 -
117
118
119 Characters from a
120
121
122 Note that you can use __pnmdepth__ To convert between a
123 the format with 1 byte per gray value and the one with 2
124 bytes per gray value.
125
126
127 There is actually another version of the PGM format that is
128 fairly rare:
129 pbm__(5) for some
130 commentary on how plain and raw formats relate to one
131 another.
132
133
134 The difference in the plain format is:
135
136
137 -
138
139
140 There is exactly one image in a file.
141
142
143 -
144
145
146 The magic number is P2 instead of P5.
147
148
149 -
150
151
152 Each pixel in the raster is represented as an ASCII decimal
153 number (of arbitrary size).
154
155
156 -
157
158
159 Each pixel in the raster has white space before and after
160 it. There must be at least one character of white space
161 between any two pixels, but there is no
162 maximum.
163
164
165 -
166
167
168 No line should be longer than 70 characters.
169
170
171 Here is an example of a small graymap in this
172 format:
173
174
175 P2
176 # feep.pgm
177 24 7
178 15
179 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
180 0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0
181 0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0
182 0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0
183 0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0
184 0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0
185 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
186 Programs that read this format should be as lenient as possible, accepting anything that looks remotely like a graymap.
187 !!COMPATIBILITY
188
189
190 Before April 2000, a raw format PGM file could not have a
191 maxval greater than 255. Hence, it could not have more than
192 one byte per sample. Old programs may depend on
193 this.
194
195
196 Before July 2000, there could be at most one image in a PGM
197 file. As a result, most tools to process PGM files ignore
198 (and don't read) any data after the first
199 image.
200 !!SEE ALSO
201
202
203 fitstopgm(1), fstopgm(1), hipstopgm(1), lispmtopgm(1),
204 psidtopgm(1), rawtopgm(1), pgmbentley(1), pgmcrater(1),
205 pgmedge(1), pgmenhance(1), pgmhist(1), pgmnorm(1),
206 pgmoil(1), pgmramp(1), pgmtexture(1), pgmtofits(1),
207 pgmtofs(1), pgmtolispm(1), pgmtopbm(1), pnm(5), pbm(5),
208 ppm(5)
209 !!AUTHOR
210
211
212 Copyright (C) 1989, 1991 by Jef Poskanzer.
213 ----
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