libpnm(3)libpnm(3)NAMElibpnm - functions to support pnm and pam programs
EXAMPLE
/* Example program fragment to read a PAM or PNM image
from stdin, add up the values of every sample in it
(I don't know why), and write the image unchanged to
stdout. */
#include <pam.h>
struct pam inpam, outpam; unsigned int row;
pnm_init(&argc, argv);
pnm_readpaminit(stdin, &inpam, sizeof(inpam));
outpam = inpam; outpam.file = stdout;
pnm_writepaminit(&outpam);
tuplerow = pnm_allocpamrow(&inpam);
for (row = 0; row < inpam.height; row++) {
unsigned int col;
pnm_readpamrow(&inpam, tuplerow);
for (column = 0; column < inpam.width; column++) {
unsigned int plane;
for (plane = 0; plane < inpam.depth; column++) {
grand_total += tuplerow[row][column][plane];
}
}
pnm_writepamrow(&outpam, tuplerow); }
pnm_freepamrow(tuplerow);
SYNOPSIS
#include <pnm.h>
void pnm_init( int *argcP, char *argv[] );
tuple ** pnm_allocpamarray( struct pam *pamP);
xel ** pnm_allocarray( int cols, int rows);
tuple * pnm_allocpamrow( struct pam *pamP);
xel * pnm_allocrow( int cols);
void pnm_freepamarray( tuple **tuplearray, struct pam *pamP);
void pnm_freearray( xel **xels, int rows);
void pnm_freepamrow( tuple *tuplerow);
void pnm_freerow( xel *xelrow);
tuple * allocpamtuple( struct pam *pamP);
void pnm_freepamtuple( tuple tuple );
void pnm_readpaminit( FILE *file, struct pam *pamP, int size);
void pnm_readpnminit( FILE *fp, int *colsP, int *rowsP, xelval *max‐
valP, int *formatP );
void pnm_readpamrow( struct pam *pamP, tuple *tuplerow);
void pnm_readpnmrow( FILE *fp, xel *xelrow, int cols,
xelval maxval, int format );
tuple ** pnm_readpam( FILE *file, struct pam *pamP,
int size);
xel ** pnm_readpnm( FILE *fp, int *colsP, int *rowsP,
xelval *maxvalP, int* formatP );"
void pnm_writepaminit( struct pam *pamP);
void pnm_writepnminit( FILE * fp , int cols, int rows, xelval maxval,
int format, int forceplain);
void pnm_writepamrow( struct pam *pamP, const tuple *tuplerow);
void pnm_writepnmrow( FILE *fp, xel *xelrow, int cols, xelval maxval,
int format, int forceplain );
void pnm_writepam( struct pam *pamP, const tuple * const *tuplearray);
void pnm_writepnm( FILE *fp, xel ** xels, int cols, int rows, xelval
maxval, int format, int forceplain );
void pnm_checkpam( struct pam *pamP, const enum pm_check_type
check_type, enum pm_check_code *retvalP);
void pnm_nextimage( FILE *file, int * const eofP);
void pnm_check( FILE * file, const enum pm_check_type check_type, const
int format, const int cols, const int rows, const xelval maxval, enum
pm_check_code *retvalP);
void pnm_promoteformatrow( xel *xelrow, int cols, xelval maxval, int
format, xelval newmaxval, int newformat);
void pnm_promoteformatrow( xel **xels, int cols, xelval maxval, int
format, xelval newmaxval, int newformat);
xel pnm_whitexel( xelval maxval, int format);
xel pnm_blackxel( xelval maxval, int format);
void pnm_invertxel( xel *x, xelval maxval, int format);
xel pnm_backgroundxelrow( xel *xelrow, int cols, xelval maxval, int
format);
xel pnm_backgroundxel( xel **xels, int cols, int rows, xelval maxval,
int format);
void pnm_YCbCrtuple( tupletuple, double *YP, double *CrP, double *CbP);
struct pam {
int size
int len
FILE * file
int format
int plainformat
int height
int width
int depth
sample maxval
int bytes_per_sample
char tuple_type[256]; }
typedef ... sample;
typedef ... tuple;
typedef ... xelval;
typedef ... xel;
extern xelval pnm_pbmmaxval;
#define PNM_MAXMAXVAL ...
#define PNM_OVERALLMAXVAL ...
#define PNM_FORMAT ...
#define PNM_ASSIGN1(x,v) ...
#define PNM_GET1(x) ...
#define PNM_EQUAL(x,y) ...
#define PAM_FORMAT_TYPE(format) ...
#define PNM_FORMAT_TYPE(format) ...
DESCRIPTION
PAM VERSUS PNM FUNCTIONS
The PNM library contains two classes of functions: The pam functions
and the pnm functions. The pam functions are enhancements of the pnm
functions and you should use them unless you need to be compatible with
older PNM libraries that don't have them (those released before August
2000).
The pnm functions operate on PBM, PGM, and PPM images and files. They
are similar to the functions in the PBM, PGM, and PPM libraries, except
the pnm functions let you operate on all three, both reading and writ‐
ing, without a lot of concern for which of the three formats you are
processing.
The pam functions provide all the same functions for operating on PBM,
PGM, and PPM libraries, but also operate on the newer PAM images and
files. The pam functions are easier to use than the pnm functions due
to improved parameter lists.
There is no separate PAM library specific to the PAM format, as there
is for PBM, PGM, and PPM.
THE pam STRUCTURE
The pam functions take most of their arguments in the form of a single
pam structure. This is not an opaque object, but just a convenient way
to organize the information upon which most the functions depend. So
you are free to access or set the elements of the structure however you
want. But you will find in most cases it is most convenient to call
pnm_readpaminit() or pnm_writepaminit() to set the fields in the pam
structure before calling any other pam functions, and then just to pass
the structure unchanged in all future calls to pam functions.
The fields are:
size The storage size in bytes of this entire structure.
len The length, in bytes, of the information in this structure. The
information starts in the first byte and is contiguous. This
cannot be greater than size. size and len can be used to make
programs compatible with newer and older versions of the Netpbm
libraries.
file The file.
format The format code of the raw image. This is PAM_FORMAT unless the
PAM image is really a view of a PBM, PGM, or PPM image. Then
it's PBM_FORMAT, RPBM_FORMAT, etc.
plainformat
This is a boolean value and means: The format above is a plain
(text) format as opposed to a raw (binary) format. This is
entirely redundant with the format member and exists as a sepa‐
rate member only for computational speed.
height The height of the image in rows.
width The width of the image in number of columns (tuples per row).
depth The depth of the image (degree of or number of samples in each
tuple).
maxval The maxval of the image. See definitions in pam(5).
bytes_per_sample
The number of bytes used to represent each sample in the image
file. See the format definition in pam(5). This is entirely
redundant with maxval. It exists as a separate member for com‐
putational speed.
tuple_type
The tuple type of the image. See definitions in pam(5). Netpbm
does not define any values for this except the following, which
are used for a PAM image which is really a view of a PBM, PGM,
or PPM image: PAM_PBM_TUPLETYPE, PAM_PGM_TUPLETYPE,
PAM_PPM_TUPLETYPE.
PLAIN VERSUS RAW FORMAT
The PNM formats each come in two varieties: the older plain (text) for‐
mat and the newer raw (binary) format. There are different format
codes for the plain and raw formats, but which of the two formats the
pnm and pam functions write is independent of the format code you pass
to them.
The pam functions always write raw formats. If you specify the format
code for a plain format, a pam function assumes instead the raw version
of that format.
The pnm functions choose between plain and raw based on the forceplain
parameter that every write-type pnm function has. If this boolean
value is true, the function writes the plain version of the format
specified by the format code. If it is false, the function writes the
raw version of the format specified by the format code.
We are trying to stamp out the older plain formats, so it would be a
wise choice not to write a program that sets forceplain true under any
circumstance. A user who needs a plain format can use the pnmto‐
plainpnm program to convert the output of your program to plain format.
PNM TYPES AND CONSTANTS
Each xel contains three xelvals, each of which should contain only the
values between 0 and PNM_MAXMAXVAL, inclusive. pnm_pbmmaxval is the
maxval used when a PNM program reads a PBM file. Normally it is 1;
however, for some programs, a larger value gives better results.
PNM XEL MANIPULATIONS
The PNM_GET1 macro extracts a single value from an xel, when you know
it's from a PBM or PGM file. When it's from a PPM file, use
PPM_GETR(), PPM_GETG(), and PPM_GETB().
The PNM_ASSIGN1 macro assigns a single value to an xel, when you know
it's from a PBM or PGM file. When it's from a PPM file, use
PPM_ASSIGN. The PNM_EQUAL macro checks two xels for equality. The
PNM_FORMAT_TYPE and PAM_FORMAT_TYPE macros compute a format type code
from a format code. The format types are PBM, PGM, PPM, and PAM. But
note that PBM, PGM, and PPM each are two different formats: a plain one
and a raw one. So there are four format types, but seven formats.
PNM_FORMAT_TYPE does not work on the PAM format code.
INITIALIZATION
All PNM and PAM programs must call pnm_init() just after startup,
before they process their arguments.
pnm_init(), among other things, processes Netpbm universal parameters
and removes them from the parameter list.
MEMORY MANAGEMENT
pnm_allocpamarray() allocates space for an array of tuples.
pnm_freepamarray() frees an array space allocated by pnm_allocpamar‐
ray() or pnm_readpam().
pnm_allocarray() allocates space for an array of xels. pnm_freearray()
frees an array space allocated by pnm_allocarray() or pnm_readpnm().
pnm_allocpamrow() allocates space for a row of a PAM image. pnm_freep‐
amrow() frees it.
pnm_allocrow() allocates space for a row of a PNM image. pnm_freerow()
frees it.
READING PNM FILES
pnm_readpaminit() reads the header of a PAM or PNM image. It returns
the information from the header in the *pamP structure. It does not
require any members of *pamP to be set at invocation, and sets every
member. size is the storage size of the *pamP structure, normally
sizeof(struct pam).
The function expects to find the image file positioned to the start of
the header and leaves it positioned to the start of the raster.
pnm_readpnminit() is similar to pnm_readpaminit(), but reads only PNM
images and has a different parameter list.
pnm_readpamrow() reads a row of the raster from a PAM or PNM image
file. It expects all of the members of the *pamP structure to be set
upon invocation and does not modify any of them. It expects to find
the file positioned to the start of the row in question in the raster
and leaves it positioned just after it. It returns the row as the
array of tuples tuplerow, which must already have its column pointers
set up so that it forms a C 2-dimensional array. The leftmost tuple is
Element 0 of this array.
pnm_readpnmrow() is similar to pnm_readpamrow() but only works on PNM
images and has a different parameter list and returns the row as an
array of xels instead of tuples.
pnm_readpam() reads an entire image from a PAM or PNM image file and
allocates the space in which to return the raster. It expects to find
the file positioned to the first byte of the image and leaves it posi‐
tioned just after the image.
The function does not require *pamP to have any of its members set and
sets them all. size is the storage size in bytes of the *pamP struc‐
ture, normally sizeof(struct pam).
The return value is a newly allocated array of the rows of the image,
with the top row being Element 0 of the array. Each row is represented
as pnm_readpamrow() would return.
The return value is also effectively a 3-dimensional C array of sam‐
ples, with the dimensions corresponding to the height, width, and depth
of the image, in that order.
pnm_readpam() combines the functions of pnm_allocpamarray(), pnm_read‐
paminit(), and iterations of pnm_readpamrow(). It may require more
dynamic storage than you can afford.
pnm_readpnm() is similar to pnm_readpam() except that it reads only PNM
images and uses a different parameter list and returns an array of rows
such that pnm_readpnmrow() would return rather than such that pnm_read‐
pamrow() would return.
WRITING FILES
pnm_writepnminit() writes the header of a PAM or PNM image and computes
some of the fields of the pam structure.
The following members of the *pamP structure must be set upon invoca‐
tion to tell the function how and what to write. size, len, file, for‐
mat, height, width, depth, maxval, tuple_type.
pnm_writepaminit() sets the plainformat and bytes_per_sample members
based on the information supplied.
pnm_writepnminit() is similar to pnm_writepaminit() except that it can
write only a PNM header and has a different parameter list.
See the description of forceplain above.
pnm_writepamrow() writes a row of the raster into a PAM or PNM image
file. It expects to find the file positioned where the row should
start and leaves it positioned just after the row. The function
requires all the elements of *pamP to be set upon invocation and
doesn't modify them.
tuplerow is an array of tuples representing the row. The leftmost
tuple is Element 0 of this array.
pnm_writepnmrow() is similar to pnm_writepamrow() except that it works
only on PNM images and has a different parameter list and takes an
array of xels instead of an array of tuples. See the description of
forceplain above.
pnm_writepam() writes an entire PAM or PNM image to a PAM or PNM image
file. It expects to find the file positioned to where the image should
start and leaves it positioned just after the image.
The following members of the *pamP structure must be set upon invoca‐
tion to tell the function how and what to write: size, len, file, for‐
mat, height, width, depth, maxval, tuple_type.
pnm_writepam() sets the plainformat and bytes_per_sample members based
on the information supplied.
tuplearray is an array of rows such that you would pass to
pnm_writepamrow(), with the top row being Element 0 of the array.
pnm_writepam() combines the functions of pnm_writepaminit(), and itera‐
tions of pnm_writepamrow(). It's raster input may be more storage than
you can afford.
pnm_writepnm() is similar to pnm_writepam() except that it works only
on PNM image, has a different parameter list, and takes an array of
rows of xels instead of an array of rows of tuples. See the descrip‐
tion of forceplain above.
MISCELLANEOUS
pnm_nextimage() positions a PNM input file to the next image in it (so
that a subsequent pnm_readpnminit() reads its header).
pnm_nextimage() is identical to pbm_nextimage().
pam_check() checks for the common file integrity error where the file
is the wrong size to contain the raster, according to the information
in the header. This works on PAM and PNM images.
pnm_check() is similar to pam_check() except it works only on PNM
images.
pnm_check() is identical to ppm_check().
PNM FORMAT PROMOTION
pnm_promoteformatrow() promotes a row of xels from one maxval and for‐
mat to a new set. Use this when you are combining multiple anymaps of
different types - just take the maximum of the maxvals and the maximum
of the formats, and promote them all to that.
pnm_promoteformat() promotes an entire anymap.
PNM XEL MANIPULATION
pnm_whitexel() and pnm_blackxel() return a white or black xel, respec‐
tively, for the given maxval and format.
pnm_invertxel() inverts an xel.
pnm_backgroundxelrow() figures out an appropriate background xel based
on the row of xels xelrow, which is cols xels wide, has maxval maxval,
and represents an image with format format.
This estimate works best when the row is the top or bottom row of the
image.
pnm_backgroundxel() does the same thing as pnm_backgroundxelrow(),
except based on an entire image instead of just one row. This tends to
do a slightly better job than pnmbackgroundxelrow().
pnm_YCbCrtuple() Returns the Y/Cb/Cr luminance/chrominance representa‐
tion of the color represented by the input tuple, assuming that the
tuple is an RGB color representation (which is the case if it was read
from a PPM image). The output components are based on the same scale
(maxval) as the input tuple, but are floating point nonetheless to
avoid losing information due to rounding. Divide them by the maxval to
get normalized [0..1] values.
SEE ALSOpbm(5), pgm(5), ppm(5), pam(5), libpbm(3), libpgm(3), libppm(3)AUTHOR
Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.
libpnm(3)
