# pgm Functions

Updated: 8 September 2007
Table Of Contents

## NAME

libpgm - libnetpbm functions to read and write PGM image files

## SYNOPSIS

#include <netpbm/pgm.h>

void pgm_init( int *argcP, char *argv[] );

gray ** pgm_allocarray( int cols, int rows );

gray * pgm_allocrow( int cols );

void pgm_freearray( gray **grays, int rows );

void pgm_freerow( gray *grayrow);

void pgm_readpgminit( FILE *fp, int *colsP, int *rowsP, gray *maxvalP, int *formatP );

void pgm_readpgmrow( FILE *fp, gray *grayrow, int cols, gray maxval, int format );

gray ** pgm_readpgm( FILE *fp, int *colsP, int *rowsP, gray *maxvalP );

void pgm_writepgminit( FILE * fp , int cols, int rows, gray maxval, int forceplain );

void pgm_writepgmrow( FILE *fp, gray *grayrow, int cols, gray maxval, int forceplain );

void pgm_writepgm( FILE *fp, gray ** grays, int cols, int rows, gray maxval, int forceplain );

void pgm_writepgm( FILE *fp, gray **grays, int cols, int rows, gray maxval, int forceplain );

void pgm_nextimage( FILE *file, int * const eofP);

void pgm_check( FILE * file, const enum pm_check_type check_type, const int format, const int cols, const int rows, const int maxval, enum pm_check_code * const retval);

typedef ... gray;

#define PGM_MAXMAXVAL ...

#define PGM_OVERALLMAXVAL ...

#define PGM_FORMAT ...

#define RPGM_FORMAT ...

#define PGM_TYPE PGM_FORMAT

#define PGM_FORMAT_TYPE(format) ...

## DESCRIPTION

These library functions are part of Netpbm.

### TYPES AND CONSTANTS

Each gray should contain only the values between 0 and PGM_OVERALLMAXVAL.

PGM_OVERALLMAXVAL is the maximum value of a maxval in a PGM file. PGM_MAXMAXVAL is the maximum value of a maxval in a PGM file that is compatible with the PGM format as it existed before April 2000. It is also the maximum value of a maxval that results in the minimum possible raster size for a particular image. I.e an image with a maxval higher than PGM_MAXMAXVAL cannot be read or generated by old PGM processing programs and requires more file space.

PGM_FORMAT is the format code for a Plain PGM format image file. RPGM_FORMAT is the format code for a Raw PGM format image file. PGM_TYPE is the format type code for the PGM formats. PGM_FORMAT_TYPE is a macro that generates code to compute the format type code of a PBM or PGM format from the format code which is its argument.

### INITIALIZATION

pgm_init() is obsolete (at least since Netpbm 9.25 (March 2002)). Use pm_proginit() instead.

pgm_init() is identical to pm_proginit.

### MEMORY MANAGEMENT

pgm_allocarray() allocates an array of grays.

pgm_allocrow() allocates a row of the given number of grays.

pgm_freearray() frees the array allocated with pgm_allocarray() containing the given number of rows.

pgm_freerow() frees a row of grays allocated with pgm_allocrow().

### READING FILES

If a function in this section is called on a PBM format file, it translates the PBM file into a PGM file on the fly and functions as if it were called on the equivalent PGM file. The format value returned by pgm_readpgminit() is, however, not translated. It represents the actual format of the PBM file.

pgm_readpgminit() reads the header of a PGM file, returning all the information from the header and leaving the file positioned just after the header.

pgm_readpgmrow() reads a row of grays into the grayrow array. format, cols, and maxval are the values returned by pgm_readpgminit().

pgm_readpgm() reads an entire PGM image into memory, returning the allocated array as its return value and returning the information from the header as rows, cols, and maxval. This function combines pgm_readpgminit(), pgm_allocarray(), and pgm_readpgmrow().

pgm_readpgminit() and pgm_readpgm abort the program with a message to Standard Error if the PGM 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 FILES

pgm_writepgminit() writes the header for a PGM file and leaves it positioned just after the header.

forceplain is a logical value that tells pgm_writepgminit() to write a header for a plain PGM format file, as opposed to a raw PGM format file.

pgm_writepgmrow() writes the row grayrow to a PGM file. For meaningful results, cols, maxval, and forceplain must be the same as was used with pgm_writepgminit().

pgm_writepgm() write the header and all data for a PGM image. This function combines pgm_writepgminit() and pgm_writepgmrow().

### MISCELLANEOUS

pgm_nextimage() positions a PGM input file to the next image in it (so that a subsequent pgm_readpgminit() reads its header).

pgm_nextimage() is analogous to pbm_nextimage(), but works on PGM and PBM files.

pgm_check() checks for the common file integrity error where the file is the wrong size to contain all the image data.

pgm_check() is analogous to pbm_check(), but works on PGM and PBM files.

## SEE ALSO

libpbm, libppm, libpnm

## Table Of Contents

- SYNOPSIS
- DESCRIPTION
  - TYPES AND CONSTANTS
  - INITIALIZATION
  - MEMORY MANAGEMENT
  - READING FILES
  - WRITING FILES
  - MISCELLANEOUS
- SEE ALSO