pbm Functions
Updated: 22 July 2004
Table Of Contents
NAMElibpbm ‐ libnetpbm functions to read and write PBM image files
SYNOPSIS
#include <pbm.h>
bit **pbm_allocarray(int cols, int rows);
bit *pbm_allocrow(int cols);
pbm_freearray(bit **bits, int rows);
pbm_freerow(bit *bitrow);
void pbm_readpbminit(FILE * fp, int *colsP, int *rowsP, int
*formatP);
void pbm_readpbmrow(FILE * fp, bit *bitrow, int cols, int for‐
mat);
void pbm_readpbmrow_packed(FILE * fp,
unsigned char * const packed_bits, const int cols, const int
format);
void bit** pbm_readpbm(FILE * fp, int *colsP, int *rowsP);
void pbm_writepbminit(FILE * fp, int cols, int rows, int for‐
ceplain);
void pbm_writepbmrow(FILE * fp, bit *bitrow, int cols, int
forceplain);
void pbm_writepbmrow_packed(FILE * fp,
unsigned char * const packed_bits, const int cols, const int
forceplain);
void pbm_writepbm(FILE * fp, bit **bits, int cols, int
rows, int
forceplain);
#define pbm_packed_bytes(cols) ...
void pbm_nextimage( FILE *file, int * const eofP);
void pbm_check( FILE * file, const enum pm_check_type
check_type, const int
format, const int cols, const int rows, enum pm_check_code *
const retval);
DESCRIPTION ‐ PBM‐SPECIFIC ROUTINES
These library functions are part of Netpbm.
TYPES AND CONSTANTS
typedef ... bit;
#define PBM_WHITE ...
#define PBM_BLACK ...
Each bit should contain only the values of PBM_WHITE or
PBM_BLACK.
#define PBM_FORMAT ...
#define RPBM_FORMAT ...
#define PBM_TYPE PBM_FORMAT
#define PBM_FORMAT_TYPE(f) ...
These are for distinguishing different file formats and types.
INITIALIZATION
pbm_init() is identical to pm_init().
MEMORY MANAGEMENT
pbm_allocarray() allocates an array of bits. pbm_allocrow()allocates a row
of the given number of bits. pbm_freearray() frees the array
allocated withpbm_allocarray() containing the given number of rows.
pbm_freerow() frees a
row of bits.
READING PBM IMAGE FILES
pbm_readpbminit() reads the header from a PBM image in a PBM
file, filling
in the rows, cols and format variables. pbm_readpbmrow() reads
a row of bits
into the bitrow array. Format and cols were filled in by
pbm_readpbminit().
pbm_readpbmrow_packed() is like pbm_readrow() except instead
of returning a
bits array, it returns an array packed_bits of bytes with the
pixels of the
image row packed into them. The pixels are in order from left
to right
across the row and from the beginning of the array to the end.
Within a
byte, the bits are in order from the most significant bit to
the least
significant bit. If the number of pixels in the row is not a
multiple of 8,
the last byte returned is padded on the least signficant bit
side with
undefined bits. White is represented by a PBM_WHITE bit; black
by PBM_BLACK.pbm_readpbm() reads an entire bitmap file into memory, re‐
turning the
allocated array and filling in the rows and cols variables.
This function
combines pbm_readpbminit(), pbm_allocarray() and pbm_readpbm‐
row().
pbm_readpbminit() and pbm_readpbm abort the program with a
message to
Standard Error if the PBM image header is not syntactically
valid, including
if it contains a number too large to be processed using the
system’s normal
data structures (to wit, a number that won’t fit in a C
’int’).
ppm_readppminit() and ppm_readppm abort the program with a
message to
Standard Error if the PPM image header is not syntactically
valid, including
if it contains a number too large to be processed using the
system’s normal
data structures (to wit, a number that won’t fit in a C
’int’).
WRITING PBM IMAGE FILES
pbm_writepbminit() writes the header for a PBM image in a
PBM file.
forceplain is a boolean value specifying that a plain format
(text) file to
be written, as opposed to a raw format (binary) one.
pbm_writepbmrow()
writes a row to a PBM file. pbm_writepbmrow_packed() is the
same aspbm_writepbmrow() except that you supply the row to write as
an array of
bytes packed with bits instead of as a bits array. The format
of packed_bits
is the same as that returned by pbm_readpbmrow().
pbm_writepbm() writes the header and all data for a PBM image
to a PBM file.
This function combines pbm_writepbminit() and pbm_writepbm‐
row().
MISCELLANEOUS
pbm_nextimage() positions a PBM input file to the next image
in it (so that
a subsequent pbm_readpbminit() reads its header).
Immediately before a call to pbm_nextimage(), the file must be
positioned
either at its beginning (i.e. nothing has been read from the
file yet) or
just after an image (i.e. as left by a pbm_readpbmrow() of the
last row in
the image).
In effect, then, all pbm_nextimage() does is test whether
there is a next
image or the file is positioned at end‐of‐file.
If pbm_nextimage() successfully positions to the next image,
it returns
*eofP false (0). If there is no next image in the file, it re‐
turns *eofP
true . If it can’t position or determine the file status due
to a file
error, it issues an error message and exits the program with
an error exit
code.
pbm_check() checks for the common file integrity error where
the file is the
wrong size to contain all the image data. pbm_check() assumes
the file is
positioned after an image header (as if pbm_readpbminit() was
the last
operation on the file). It checks the file size to see if the
number of
bytes left in the file are the number required to contain the
image raster.
If the file is too short, pbm_check() causes the program to
exit with an
error message and error completion code. Otherwise, it returns
one of the
following values (enumerations of the enum pm_check_code type)
as *retval:
PM_CHECK_OK
The file’s size is exactly what is required to hold the
image raster.
PM_CHECK_UNKNOWN_TYPE
format is not a format whose size pbm_check() can an‐
ticipate. The
only format with which pbm_check() can deal is raw PBM
format.
PM_CHECK_TOO_LONG
The file is longer than it needs to be to contain the
image raster.
The extra data might be another image.
PM_CHECK_UNCHECKABLE
The file is not a kind that has a predictable size, so
there is no
simple way for pbm_check() to know if it is the right
size. Only a
regular file has predictable size. A pipe is a common
example of a
file that does not.
check_type must have the value PM_CHECK_BASIC (an enumerated
value of the
pm_check_type enumerated type). Otherwise, the effect of
pbm_check() is
unpredictable. This argument exists for future backward com‐
patible expansion
of the function of pbm_check().
SEE ALSO
libpgm, libppm, libpnm, pbm
AUTHOR
Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.
_________________________________________________________________
Table Of Contents
* DESCRIPTION ‐ PBM‐SPECIFIC ROUTINES
+ TYPES AND CONSTANTS
+ INITIALIZATION
+ MEMORY MANAGEMENT
+ READING PBM IMAGE FILES
+ WRITING PBM IMAGE FILES
+ MISCELLANEOUS
* SEE ALSO
* AUTHOR
