libnetpbm
Updated: December 2003
libnetpbm is a C programming library for reading, writing, and
manipulating
Netpbm images. It also contains a few general graphics manipu‐
lation tools,
but it is not intended to be a graphics tools library. For
graphics tools,
Netpbm expects you to run the Netpbm programs. From a C pro‐
gram, the
libnetpbm function pm_system() makes this easy. However, since
it creates a
process and execs a program, this may be too heavyweight
for some
applications.
To use libnetpbm services in your C program, #include the
pam.h interface
header file. For historical reasons, you can also get by in
some cases with
pbm.h, pgm.h, ppm.h, or pnm.h, but there’s really no point to
that anymore.
The libnetpbm functions are divided into these categories:
* PBM functions. These have names that start with pbm and
work only on PBM
images.
* PGM functions. These have names that start with pgm and
work only on PGM
images.
* PPM functions. These have names that start with ppm and
work only on PPM
images.
* PNM functions. These have names that start with pnm and
work on PBM,
PGM, and PPM images.
* PAM functions. These also have names that start with pnm
and work on all
the Netpbm image types.
* PM functions. These are utility functions that aren’t spe‐
cific to any
particular image format.
For new programming, you rarely need to concern yourself with
the PBM, PGM,
PPM, and PNM functions, because the newer PAM functions do the
same thing
and are easier to use. For certain processing of bi‐level im‐
ages, the PBM
functions are significantly more efficient, though.
libnetpbm has a backward compatibility feature that means a
function
designed to read one format can read some others too, convert‐
ing on the fly.
In particular, a function that reads a PGM image will also
read a PBM image,
but converts it as it reads it so that for programming purpos‐
es, it is a PGM
image. Similarly, a function that reads PPM can read PBM and
PGM as well.
And a function that reads PBM, PGM, or PPM can read a PAM
that has an
equivalent tuple type.
For each of the five classes of libnetpbm image processing
functions,
libnetpbm has in in‐memory representation for a pixel, a row,
and a whole
image. Do not confuse this format with the actual image for‐
mat, as you would
see in a file. The libnetpbm in‐memory format is designed
to make
programming very easy. It is sometimes extremely inefficient,
even more than
the actual image format. For example, a pixel that a PPM image
represents
with 3 bytes, libnetpbm’s PAM functions represent with 16
bytes. A pixel in
a PBM image is represented by a single bit, but the PNM func‐
tions represent
that pixel in memory with 96 bits.
See Libnetpbm User’s Manual for the basics on using libnetpbm
in a program.
You can look up the reference information for a particular
function in The
libnetpbm Directory.
Before Netpbm release 10 (June 2002), this library was split
into four:
libpbm, libpgm, libppm, and libpnm. That’s largely the reason
for the
multiple sets of functions and scattered documentation.
