1The PBM Format(5) File Formats Manual The PBM Format(5)
2
6 pbm - Netpbm bi-level image format
7
10 This program is part of Netpbm(1).
11 The PBM format is a lowest common denominator monochrome file format.
13 It serves as the common language of a large family of bitmap image con‐
14 version filters. Because the format pays no heed to efficiency, it is
15 simple and general enough that one can easily develop programs to con‐
16 vert to and from just about any other graphics format, or to manipulate
17 the image.
18 The name "PBM" is an acronym derived from "Portable Bit Map."
20 This is not a format that one would normally use to store a file or to
22 transmit it to someone -- it's too expensive and not expressive enough
23 for that. It's just an intermediary format. In it's purest use, it
24 lives only in a pipe between two other programs.
25
28 The format definition is as follows.
29 A PBM file consists of a sequence of one or more PBM images. There are
31 no data, delimiters, or padding before, after, or between images.
32 Each PBM image consists of the following:
34 • A "magic number" for identifying the file type. A pbm image's
39 magic number is the two characters "P4".
40 • Whitespace (blanks, TABs, CRs, LFs).
43 • The width in pixels of the image, formatted as ASCII characters
46 in decimal.
47 • Whitespace.
50 • The height in pixels of the image, again in ASCII decimal.
53 • A single whitespace character (usually a newline).
56 • A raster of Height rows, in order from top to bottom. Each row
59 is Width bits, packed 8 to a byte, with don't care bits to fill
60 out the last byte in the row. Each bit represents a pixel: 1 is
61 black, 0 is white. The order of the pixels is left to right.
62 The order of their storage within each file byte is most signif‐
63 icant bit to least significant bit. The order of the file bytes
64 is from the beginning of the file toward the end of the file.
65 A row of an image is horizontal. A column is vertical. The
67 pixels in the image are square and contiguous.
68 • Before the whitespace character that delimits the raster, any
71 characters from a "#" through the next carriage return or new‐
72 line character, is a comment and is ignored. Note that this is
73 rather unconventional, because a comment can actually be in the
74 middle of what you might consider a token. Note also that this
75 means if you have a comment right before the raster, the newline
76 at the end of the comment is not sufficient to delimit the
77 raster.
78 All characters referred to herein are encoded in ASCII. "newline"
82 refers to the character known in ASCII as Line Feed or LF. A "white
83 space" character is space, CR, LF, TAB, VT, or FF (I.e. what the ANSI
84 standard C isspace() function calls white space).
85 Plain PBM
89 There is actually another version of the PBM format, even more simplis‐
90 tic, more lavishly wasteful of space than PBM, called Plain PBM. Plain
91 PBM actually came first, but even its inventor couldn't stand its reck‐
92 lessly squanderous use of resources after a while and switched to what
93 we now know as the regular PBM format. But Plain PBM is so redundant
94 -- so overstated -- that it's virtually impossible to break. You can
95 send it through the most liberal mail system (which was the original
96 purpose of the PBM format) and it will arrive still readable. You can
97 flip a dozen random bits and easily piece back together the original
98 image. And we hardly need to define the format here, because you can
99 decode it by inspection.
100 Netpbm programs generate Raw PBM format instead of Plain PBM by de‐
102 fault, but the common option ⟨index.html#commonoptions⟩ -plain chooses
103 Plain PBM.
104 The difference is:
106 •
109 There is exactly one image in a file.
111 •
113 The "magic number" is "P1" instead of "P4".
115 •
117 Each pixel in the raster is represented by a byte containing
119 ASCII '1' or '0', representing black and white respectively.
120 There are no fill bits at the end of a row.
121 •
123 White space in the raster section is ignored.
125 •
127 You can put any junk you want after the raster, if it starts
129 with a white space character.
130 •
132 No line should be longer than 70 characters.
134 Here is an example of a small image in the plain PBM format.
137 P1
138 # feep.pbm
139 24 7
140 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
141 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0
142 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0
143 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0
144 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
145 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 0 0 0 0
146 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
147 There is a newline character at the end of each of these lines.
150 You can generate the Plain PBM format from the regular PBM format
152 (first image in the file only) with the pnmtoplainpnm program.
153 Programs that read this format should be as lenient as possible, ac‐
155 cepting anything that looks remotely like a bitmap.
156
160 No Internet Media Type (aka MIME type, content type) for PBM has been
161 registered with IANA, but the value image/x-portable-bitmap is conven‐
162 tional.
163 Note that the PNM Internet Media Type image/x-portable-anymap also ap‐
165 plies.
166
170 There are no requirements on the name of a PBM file, but the convention
171 is to use the suffix ".pbm". "pnm" is also conventional, for cases
172 where distinguishing between the particular subformats of PNM is not
173 convenient.
174
178 Before July 2000, there could be at most one image in a PBM file. As a
179 result, most tools to process PBM files ignore (and don't read) any
180 data after the first image.
181
184 libnetpbm(1), pnm(1), pgm(1), ppm(1), pam(1), programs that process
185 PBM(1)
186
188 This manual page was generated by the Netpbm tool 'makeman' from HTML
189 source. The master documentation is at
190 http://netpbm.sourceforge.net/doc/pbm.html
192netpbm documentation 27 November 2013 The PBM Format(5)