.TH ppm 5 "27 September 1991"
.SH NAME
ppm - portable pixmap file format
.SH DESCRIPTION
The portable pixmap format is a lowest common denominator color image
file format.
.IX "PPM file format"
The definition is as follows:
.IP - 2
A "magic number" for identifying the file type.
A ppm file's magic number is the two characters "P3".
.IX "magic numbers"
.IP - 2
Whitespace (blanks, TABs, CRs, LFs).
.IP - 2
A width, formatted as ASCII characters in decimal.
.IP - 2
Whitespace.
.IP - 2
A height, again in ASCII decimal.
.IP - 2
Whitespace.
.IP - 2
The maximum color-component value, again in ASCII decimal.
.IP - 2
Whitespace.
.IP - 2
Width * height pixels, each three ASCII decimal values between 0 and the
specified maximum value, starting at the 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.
.IP - 2
Characters from a "#" to the next end-of-line are ignored (comments).
.IP - 2
No line should be longer than 70 characters.
.PP
Here is an example of a small pixmap in this format:
.nf
P3
# feep.ppm
4 4
15
 0  0  0    0  0  0    0  0  0   15  0 15
 0  0  0    0 15  7    0  0  0    0  0  0
 0  0  0    0  0  0    0 15  7    0  0  0
15  0 15    0  0  0    0  0  0    0  0  0
.fi
.PP
Programs that read this format should be as lenient as possible,
accepting anything that looks remotely like a pixmap.
.PP
There is also a "rawbits" variant on the format.
This variant is different in the following ways:
.IP - 2
The "magic number" is "P6" instead of "P3".
.IP - 2
The pixel values are stored as plain bytes, instead of ASCII decimal.
.IP - 2
No whitespace is allowed in the pixels section, and only a single character
of whitespace, typically a newline, is allowed after the maxval.
(This last requirement is actually due to a botch in the design of
the file format.)
.IP - 2
The files are smaller and many times faster to read and write.
.PP
If maxval is between 256 and 65535, the pixel values are stored as
two bytes, low byte first and high byte second.
Images with maxval higher than 65535 must be written in the slower
but more general plain format.
.SH "SEE ALSO"
pbmplus(1),
pbm(5), pgm(5), pnm(5)
.SH AUTHOR
Copyright (C) 1989, 1991, 1999 by Jef Poskanzer.
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