PPM Image Format
taken from "man ppm"
Name
ppm - portable pixmap file format
Description
The portable pixmap format is a lowest common denominator
color image file format. The definition is as follows:
- A "magic number" for identifying the file type. A ppm
file's magic number is the two characters "P3".
- Whitespace (blanks, TABs, CRs, LFs).
- A width, formatted as ASCII characters in decimal.
- Whitespace.
- A height, again in ASCII decimal.
- Whitespace.
- The maximum color-component value, again in ASCII decimal.
- Whitespace.
- 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.
- Characters from a "#" to the next end-of-line are ignored
(comments).
- No line should be longer than 70 characters.
Here is an example of a small pixmap in this format:
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
Programs that read this format should be as lenient as
possible, accepting anything that looks remotely like a
pixmap.
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:
- The "magic number" is "P6" instead of "P3".
- The pixel values are stored as plain bytes, instead of
ASCII decimal.
- Whitespace is not allowed in the pixels area, and only a
single character of whitespace (typically a newline) is
allowed after the maxval.
- The files are smaller and many times faster to read and
write.
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
write a file with a larger maxval, it will automatically
fall back on the slower but more general plain format.
See Also
giftoppm(1), gouldtoppm(1), ilbmtoppm(1), imgtoppm(1),
mtvtoppm(1), pcxtoppm(1), pgmtoppm(1), pi1toppm(1),
picttoppm(1), pjtoppm(1), qrttoppm(1), rawtoppm(1),
rgb3toppm(1), sldtoppm(1), spctoppm(1), sputoppm(1),
tgatoppm(1), ximtoppm(1), xpmtoppm(1), yuvtoppm(1),
ppmtoacad(1), ppmtogif(1), ppmtoicr(1), ppmtoilbm(1),
ppmtopcx(1), ppmtopgm(1), ppmtopi1(1), ppmtopict(1),
ppmtopj(1), ppmtopuzz(1), ppmtorgb3(1), ppmtosixel(1),
ppmtotga(1), ppmtouil(1), ppmtoxpm(1), ppmtoyuv(1),
ppmdither(1), ppmforge(1), ppmhist(1), ppmmake(1),
ppmpat(1), ppmquant(1), ppmquantall(1), ppmrelief(1),
pnm(5), pgm(5), pbm(5)
Author
Copyright (C) 1989, 1991 by Jef Poskanzer.
Dan Wallach, CS Department, Princeton University
Last modified: Tue Nov 28 16:06:21 EST 1995