pnm Functions

Updated: 22 July 2004
Table Of Contents

NAME

libpnm - libnetpbm functions to read and write PNM image files

SYNOPSIS

#include <pnm.h>

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

xel ** pnm_allocarray( int cols, int rows);

xel * pnm_allocrow( int cols);

void pnm_freearray( xel **xels, int rows);

void pnm_freerow( xel *xelrow);

void pnm_readpnminit( FILE *fp, int *colsP, int *rowsP, xelval *maxvalP, int *formatP );

void pnm_readpnmrow( FILE *fp, xel *xelrow, int cols,
xelval maxval, int format );

xel ** pnm_readpnm( FILE *fp, int *colsP, int *rowsP,
xelval *maxvalP, int* formatP );

void pnm_writepnminit( FILE * fp , int cols, int rows, xelval maxval, int format, int forceplain);

void pnm_writepnmrow( FILE *fp, xel *xelrow, int cols, xelval maxval, int format, int forceplain );

void pnm_writepnm( FILE *fp, xel ** xels, int cols, int rows, xelval maxval, int format, int forceplain );

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_promoteformat( 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);

typedef ... xelval;

typedef ... xel;

extern xelval pnm_pbmmaxval;

#define PNM_ASSIGN1(x,v) ...

#define PNM_GET1(x) ...

#define PNM_EQUAL(x,y) ...

#define PNM_FORMAT_TYPE(format) ...

DESCRIPTION

These library functions are part of Netpbm.

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 macro computes 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

pnm_init is identical to pm_init().

MEMORY MANAGEMENT

pnm_allocarray() allocates space for an array of xels. pnm_freearray() frees an array space allocated by pnm_allocarray() or pnm_readpnm().

pnm_allocrow() allocates space for a row of a PNM image. pnm_freerow() frees it.

READING PNM FILES

pnm_readpnminit() is similar to pnm_readpaminit(), but reads only PNM images and has a different parameter list.

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_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_readpamrow() would return.

WRITING FILES

pnm_writepnminit() is similar to pnm_writepaminit() except that it can write only a PNM header and has a different parameter list.

forceplain is a binary value. True (nonzero) means to write the image in the plain (ASCII) version of the selected format. False (zero) means to write it in the raw (binary) version of the selected format. See PNM format specification.

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_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 description of forceplain above.

MISCELLANEOUS

pnm_check() is similar to pnm_checkpam() 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 format 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, respectively, 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().