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 The format definition is as follows.
27 A PBM file consists of a sequence of one or more PBM images. There are
29 no data, delimiters, or padding before, after, or between images.
30 Each PBM image consists of the following:
32 · A 'magic number' for identifying the file type. A pbm image's
37 magic number is the two characters 'P4'.
38 · Whitespace (blanks, TABs, CRs, LFs).
41 · The width in pixels of the image, formatted as ASCII characters
44 in decimal.
45 · Whitespace.
48 · The height in pixels of the image, again in ASCII decimal.
51 · A single whitespace character (usually a newline).
54 · A raster of Height rows, in order from top to bottom. Each row
57 is Width bits, packed 8 to a byte, with don't care bits to fill
58 out the last byte in the row. Each bit represents a pixel: 1 is
59 black, 0 is white. The order of the pixels is left to right.
60 The order of their storage within each file byte is most signif‐
61 icant bit to least significant bit. The order of the file bytes
62 is from the beginning of the file toward the end of the file.
63 A row of an image is horizontal. A column is vertical. The
65 pixels in the image are square and contiguous.
66 · Before the whitespace character that delimits the raster, any
69 characters from a '#' through the next carriage return or new‐
70 line character, is a comment and is ignored. Note that this is
71 rather unconventional, because a comment can actually be in the
72 middle of what you might consider a token. Note also that this
73 means if you have a comment right before the raster, the newline
74 at the end of the comment is not sufficient to delimit the
75 raster.
76 There is actually another version of the PBM format, even more simplis‐
80 tic, more lavishly wasteful of space than PBM, called Plain PBM. Plain
81 PBM actually came first, but even its inventor couldn't stand its reck‐
82 lessly squanderous use of resources after a while and switched to what
83 we now know as the regular PBM format. But Plain PBM is so redundant
84 -- so overstated -- that it's virtually impossible to break. You can
85 send it through the most liberal mail system (which was the original
86 purpose of the PBM format) and it will arrive still readable. You can
87 flip a dozen random bits and easily piece back together the original
88 image. And we hardly need to define the format here, because you can
89 decode it by inspection.
90 Netpbm programs generate Raw PBM format instead of Plain PBM by
92 default, but the common option ⟨index.html#commonoptions⟩ -plain
93 chooses Plain PBM.
94 The difference is:
96 - There is exactly one image in a file.
99 - The 'magic number' is 'P1' instead of 'P4'.
101 - Each pixel in the raster is represented by a byte containing
103 ASCII '1' or '0', representing black and white respectively.
104 There are no fill bits at the end of a row.
105 - White space in the raster section is ignored.
107 - You can put any junk you want after the raster, if it starts
109 with a white space character.
110 - No line should be longer than 70 characters.
112 Here is an example of a small image in the plain PBM format.
115 P1
116 # feep.pbm
117 24 7
118 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
119 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0
120 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0
121 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0
122 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
123 0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 0 0 0 0
124 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
125 There is a newline character at the end of each of these lines.
127 You can generate the Plain PBM format from the regular PBM format
129 (first image in the file only) with the pnmtoplainpnm program.
130 Programs that read this format should be as lenient as possible,
132 accepting anything that looks remotely like a bitmap.
133 All characters referred to herein are encoded in ASCII. 'newline'
135 refers the the character known in ASCII as Line Feed or LF. A 'white
136 space' character is space, CR, LF, TAB, VT, or FF (I.e. what the ANSI
137 standard C isspace() function calls white space).
138
141 Before July 2000, there could be at most one image in a PBM file. As a
142 result, most tools to process PBM files ignore (and don't read) any
143 data after the first image.
144
147 libnetpbm(1), pnm(1), pgm(1), ppm(1), pam(1), programsthatprocessPBM[1m(1)
148netpbm documentation 22 September 2006 The PBM Format(5)