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pnm_io.h File Reference

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Detailed Description

Input routines for PNM, PPM, PGM, and PBM files.

Header

/u/nn/cvsroot/lissom/src/pnm_io.h,v 1.18 2002/03/23 20:02:50 jbednar Exp

Definition in file pnm_io.h.

#include <string>
#include <fstream>
#include <utility>

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Defines
#define	IFSTREAM   std::ifstream
Functions
std::istream &	eatcomments (std::istream &is)
	Swallows comments from the given stream, where a comment is defined as a line whose first non-whitespace character is a pound sign (#).
template<class Array2D> bool	pgm_read (const string &filename, Array2D &image)
	Read the specified PBM or PGM file into the given matrix in column-major order.
std::pair< int, int >	pnm_size (const string &filename)
	Utility routine which returns the size of the given PNM file as a (width,height) if found and readable, or else (0,0).
bool	pgm_white_is_transparent (const string &filename)
	Utility routine which returns true if the file declares that white (i.e.

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Function Documentation

template<class Array2D> bool pgm_read (  const string &    filename, Array2D &    image )

Read the specified PBM or PGM file into the given matrix in column-major order. Any 2D array type which supports a (width,height) constructor should work, e.g. TNT's Matrix. Returns false if there was a problem reading the file. Definition at line 54 of file pnm_io.h. References eatcomments(). Referenced by KernelFactory::create().

bool pgm_white_is_transparent (  const string &    filename )  [inline]

Utility routine which returns true if the file declares that white (i.e. 255/255) pixels are to be considered transparent. The PNM specs do not provide for transparency, but as a convention I assume that if the file has a comment (all on one line) of the form: #Transparent: 255 then then I should consider it so. The comment must appear within the first two non-comment lines to be detected, there must be no space after the #, and there must be one space after the :. Only a value of 255 (pure white) is supported at present. The reason is that pgm_read returns floats, not discrete integers, so it's more complicated to check any pixel value other than pure white or black. (One would have to check a range half a pixel-value-step larger and smaller in each direction.) In any case, in a non-colormapped grayscale picture, only black and white are likely to be useful as transparent. (Otherwise there would be a big step in grayscale gradients somewhere.) Definition at line 174 of file pnm_io.h.

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