libpbm(3)libpbm(3)NAMElibpbm - functions to read and write PBM image files
SYNOPSIS
#include <pbm.h>
int pm_keymatch(char * str, char * keyword, int minchars);
int pm_maxvaltobits(int maxval);
int pm_bitstomaxval(int bits);
unsigned int pm_lcm(unsigned int x, unsigned int y,
unsigned int z, unsigned int limit);
void pm_message(char * fmt, ... );
void pm_error(char * fmt, ... );
void pm_perror(char * fmt, ... );
void pm_usage(char * usage);
FILE *pm_openr(char * name)
FILE *pm_openw(char * name);
FILE *pm_openr_seekable(const char * name);
FILE *pm_close(FILE * fp);
char *pm_read_unknown_size(FILE * fp, long *nread);
unsigned int pm_tell(FILE * fileP);
void pm_seek(FILE * fileP, unsigned long filepos);
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
format);
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
forceplain);
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);
int pm_readbigshort(FILE *in, short *sP);
int pm_writebigshort(FILE *out, short s);
int pm_readbiglong(FILE *in, long *lP);
int pm_writebiglong(FILE *out, long l);
int pm_readlittleshort(FILE *in, short *sP);
int pm_writelittleshort(FILE *out, short s);
int pm_readlittlelong(FILE *in, long *lP);
int pm_writelittlelong(FILE *out, long l);
DESCRIPTION - PACKAGE-WIDE ROUTINES
KEYWORD MATCHING
pm_keymatch() does a case-insensitive match of str against
keyword. str can be a leading sunstring of keyword, but
at least minchars must be present.
MAXVAL ARITHMETIC
pm_maxvaltobits() and pm_bitstomaxval() convert between a
maxval and the minimum number of bits required to hold it.
pm_lcm() computes the least common multiple of 3 integers.
You also specify a limit and if the LCM would be higher
than that limit, pm_lcm() just returns that limit.
MESSAGES AND ERRORS
pm_message() is a printf() style routine to write an
informational message to the Standard Error file stream.
pm_message() suppresses the message, however, if the user
specified the -quiet option on the command line. See the
initialization functions, e.g. pbm_init(), for informa
tion on the -quiet option. Note that Netpbm programs are
often used interactively, but also often used by programs.
In the interactive case, it is nice to issue messages
about what the program is doing, but in the program case,
such messages are usually undesirable. By using pm_mes
sage() for all your messages, you make your program usable
in both cases. Without any effort on your part, program
users of your program can avoid the messages by specifying
the -quiet option.
pm_error() is a printf() style routine that writes an
error message to the Standard Error file stream and exits
the program with an exit code of 1.
GENERIC FILE ACCESS
pm_openr() opens the given file for reading, with appro
priate error checking. A filename of - is taken to mean
Standard Input. pm_openw() opens the given file for writ
ing, with appropriate error checking. pm_close() closes
the file descriptor, with appropriate error checking.
pm_openr_seekable() appears to open the file just like
pm_openr(), but the file thus opened is guaranteed to be
seekable (you can use ftell() and fseek() on it).
pm_openr_seekable() pulls this off by copying the entire
file to a temporary file and giving you the handle of the
temporary file, if it has to. If the file you name is a
regular file, it's already seekable so pm_openr_seekable()
just does the same thing as pm_openr(). But if it is,
say, a pipe, it isn't seekable. So pm_openr_seekable()
reads the pipe until EOF into a temporary file, then opens
that temporary file and returns the handle of the tempo
rary file. The temporary file is seekable.
The file pm_openr_seekable() creates is one that the oper
ating system recognizes as temporary, so when you close
the file, by any means, it gets deleted.
You need a seekable file if you intend to make multiple
passes through the file. The only alternative is to read
the entire image into memory and work from that copy.
That may use too much memory. Note that the image takes
less space in the file cache than in a buffer in memory.
As much as 96 times less space! Each sample is an integer
in the buffer, which is usually 96 bits. In the file, a
sample may be as small as 1 bit and rarely more than 8
bits.
pm_read_unknown_size() reads an entire file or input
stream of unknown size to a buffer. Allocate memory more
memory as needed. The calling routine has to free the
allocated buffer with free().
pm_read_unknown_size() returns a pointer to the allocated
buffer. The nread argument returns the number of bytes
read.
pm_tell() returns a handle for the current position of the
file, whether it be the header or a row of the raster.
Use the handle as an argument to pm_seek() to reposition
the file there later. The file must be seekable (which
you can ensure by opening it with pm_openr_seek
able())orthismayfail.
ENDIAN I/O
pm_readbigshort(), pm_writebigshort(), pm_readbiglong(),
pm_writebiglong(), pm_readlittleshort(), pm_writelit
tleshort(), pm_readlittlelong(), and pm_writelittlelong()
are routines to read and write short and long ints in
either big- or little-endian byte order. The return value
is 0 upon success and -1 upon failure (either EOF or I/O
error).
DESCRIPTION - PBM-SPECIFIC ROUTINES
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
All PBM programs must call pbm_init just after invocation,
before processing arguments.
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 with
pbm_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_readpb
minit(). 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 signf
icant 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,
returning the allocated array and filling in the rows and
cols variables. This function combines pbm_readpbminit(),
pbm_allocarray() and pbm_readpbmrow().
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 as
pbm_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_writepb
minit() and pbm_writepbmrow().
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 returns *eofP true (1). 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 opera
tion 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 mes
sage 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
anticipate. 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 enumer
ated value of the pm_check_type enumerated type). Other
wise, the effect of pbm_check() is unpredictable. This
argument exists for future backward compatible expansion
of the function of pbm_check().
SEE ALSOlibpgm(3), libppm(3), libpnm(3), pbm(5)AUTHOR
Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.
libpbm(3)
