NAME¶
libpbm - 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
information 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_message() 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 appropriate error
checking. A filename of
- is taken to mean Standard Input.
pm_openw() opens the given file for writing, 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 temporary file.
The temporary file is seekable.
The file
pm_openr_seekable() creates is one that the operating 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_seekable())
orthis
mayfail.
ENDIAN I/O¶
pm_readbigshort(),
pm_writebigshort(),
pm_readbiglong(),
pm_writebiglong(),
pm_readlittleshort(),
pm_writelittleshort(),
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_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, 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_writepbminit() 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 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 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 enumerated value
of the
pm_check_type enumerated type). Otherwise, the effect of
pbm_check() is unpredictable. This argument exists for future backward
compatible expansion of the function of
pbm_check().
SEE ALSO¶
libpgm(3),
libppm(3),
libpnm(3),
pbm(5)
AUTHOR¶
Copyright (C) 1989, 1991 by Tony Hansen and Jef Poskanzer.