Manual Reference Pages - ppm (5)
NAME
ppm - portable pixmap file format
CONTENTS
Description
Author
DESCRIPTION
The portable pixmap format is a lowest common denominator
color image file format. The definition is as follows:
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A "magic number" for identifying the file type. A ppm
file’s magic number is the two characters "P3".
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Whitespace (blanks, TABs, CRs, LFs).
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A width, formatted as ASCII characters in decimal.
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Whitespace.
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A height, again in ASCII decimal.
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Whitespace.
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The maximum color-component value, again in ASCII decimal.
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Whitespace.
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Width * height pixels, each three ASCII decimal values
between 0 and the specified maximum value, starting at the
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top-left corner of the pixmap, | | |
proceeding in normal
English reading order. The three values for each pixel
represent red, green, and blue, respectively; a value of 0
means that color is off, and the maximum value means that
color is maxxed out.
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Characters from a "#" to the next end-of-line are ignored
(comments).
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No line should be longer than 70 characters.
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Here is an example of a small pixmap in this format:
P3
# feep.ppm
4 4
15
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0 0 0 0 0 0 0 0 15 0 15
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0 0 0 15 7 0 0 0 0 0 0
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0 0 0 0 0 0 15 7 0 0 0
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0 15 0 0 0 0 0 0 0 0 0
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Programs that read this format should be as lenient as possible,
accepting anything that looks remotely like a pixmap.
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There is also a variant on the format, available by setting
the RAWBITS option at compile time. This variant is
different in the following ways:
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The "magic number" is "P6" instead of "P3".
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The pixel values are stored as plain bytes, instead of
ASCII decimal.
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Whitespace is not allowed in the pixels area, and only a
single character of whitespace (typically a newline) is
allowed after the maxval.
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The files are smaller and many times faster to read and
write.
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Note that this raw format can only be used for maxvals less
than or equal to 255. If you use the ppm library and try to
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write a file with a larger maxval, |
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it will automatically
fall back on the slower but more general plain format.
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AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
Last change: 27 September 1991
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