io_png.c File Reference

PNG read/write simplified interface. More...

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <assert.h>
#include <png.h>
#include "io_png.h"

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Defines
#define	PNG_SIG_LEN 4
#define	IO_PNG_U8 0x0001
#define	IO_PNG_F32 0x0002
Functions
char *	io_png_info (void)
	helps tracking versions, via the string tag inserted into the library
static void *	io_png_read_abort (FILE fp, png_structp png_ptr_p, png_infop *info_ptr_p)
	internal function used to cleanup the memory when png_read_raw() fails
static void *	io_png_read_raw (const char fname, size_t nxp, size_t nyp, size_t ncp, int png_transform, int dtype)
	internal function used to read a PNG file into an array
unsigned char *	io_png_read_u8 (const char fname, size_t nxp, size_t nyp, size_t ncp)
	read a PNG file into a 8bit integer array
unsigned char *	io_png_read_u8_rgb (const char fname, size_t nxp, size_t *nyp)
	read a PNG file into a 8bit integer array, converted to RGB
unsigned char *	io_png_read_u8_gray (const char fname, size_t nxp, size_t *nyp)
	read a PNG file into a 8bit integer array, converted to gray
float *	io_png_read_f32 (const char fname, size_t nxp, size_t nyp, size_t ncp)
	read a PNG file into a 32bit float array
float *	io_png_read_f32_rgb (const char fname, size_t nxp, size_t *nyp)
	read a PNG file into a 32bit float array, converted to RGB
float *	io_png_read_f32_gray (const char fname, size_t nxp, size_t *nyp)
	read a PNG file into a 32bit float array, converted to gray
static int	io_png_write_abort (FILE fp, png_byte idata, png_bytep row_pointers, png_structp png_ptr_p, png_infop *info_ptr_p)
	internal function used to cleanup the memory when png_write_raw() fails
static int	io_png_write_raw (const char fname, const void data, size_t nx, size_t ny, size_t nc, int dtype)
	internal function used to write a byte array as a PNG file
int	io_png_write_u8 (const char fname, const unsigned char data, size_t nx, size_t ny, size_t nc)
	write a 8bit unsigned integer array into a PNG file
int	io_png_write_f32 (const char fname, const float data, size_t nx, size_t ny, size_t nc)
	write a float array into a PNG file
Variables
static char	io_png_tag [] = "using io_png " IO_PNG_VERSION

Detailed Description

PNG read/write simplified interface.

This is a front-end to libpng, with routines to:

read a PNG file as a deinterlaced 8bit integer or float array
write a 8bit integer or float array to a PNG file

Multi-channel images are handled: grey, grey+alpha, rgb and rgb+alpha, as well as on-the-fly color model conversion.

Todo:

handle lossless 16bit data

add a test suite

internally handle RGB/gray conversion in io_png_read_raw()

handle deinterlacing as a libpng transform function

Author:: Nicolas Limare <nicolas.limare@cmla.ens-cachan.fr>

Definition in file io_png.c.

Define Documentation

#define IO_PNG_F32 0x0002

Definition at line 54 of file io_png.c.

#define IO_PNG_U8 0x0001

Definition at line 53 of file io_png.c.

#define PNG_SIG_LEN 4

Definition at line 50 of file io_png.c.

Function Documentation

char* io_png_info ( void )

helps tracking versions, via the string tag inserted into the library

This function is not expected to be used in real-world programs.

Returns:: a pointer to a version info string

Definition at line 70 of file io_png.c.

static void* io_png_read_abort	(	FILE *	fp,
		png_structp *	png_ptr_p,
		png_infop *	info_ptr_p
	)			`[static]`

internal function used to cleanup the memory when png_read_raw() fails

Parameters:

	fp	file pointer to close, ignored if NULL
	png_ptr_p,info_ptr_p,pointers	to PNG structure pointers, ignored if NULL

Returns:: NULL

Definition at line 87 of file io_png.c.

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float* io_png_read_f32	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp,
		size_t *	ncp
	)

read a PNG file into a 32bit float array

The array contains the deinterlaced channels. 1, 2, 4 and 8bit images are converted to float values between 0. and 1., 3., 15. or 255. 16bit images are also downscaled to 8bit before conversion.

Parameters:

	fname	PNG file name
	nxp,nyp,ncp	pointers to variables to be filled with the number of columns, lines and channels of the image

Returns:: pointer to an allocated unsigned char array of pixels, or NULL if an error happens

Definition at line 364 of file io_png.c.

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float* io_png_read_f32_gray	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp
	)

read a PNG file into a 32bit float array, converted to gray

See io_png_read_f32() for details.

Definition at line 415 of file io_png.c.

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float* io_png_read_f32_rgb	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp
	)

read a PNG file into a 32bit float array, converted to RGB

See io_png_read_f32() for details.

Definition at line 376 of file io_png.c.

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static void* io_png_read_raw	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp,
		size_t *	ncp,
		int	png_transform,
		int	dtype
	)			`[static]`

internal function used to read a PNG file into an array

Todo:: don't loose 16bit info

Parameters:

	fname	PNG file name, "-" means stdin
	nxp,nyp,ncp	pointers to variables to be filled with the number of columns, lines and channels of the image
	png_transform	a PNG_TRANSFORM flag to be added to the default libpng read transforms
	dtype	identifier for the data type to be used for output

Returns:: pointer to an allocated array of pixels, or NULL if an error happens

Definition at line 110 of file io_png.c.

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unsigned char* io_png_read_u8	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp,
		size_t *	ncp
	)

read a PNG file into a 8bit integer array

The array contains the deinterlaced channels. 1, 2 and 4bit images are converted to 8bit. 16bit images are previously downscaled to 8bit.

Todo:: don't downscale 16bit images.

Parameters:

	fname	PNG file name
	nxp,nyp,ncp	pointers to variables to be filled with the number of columns, lines and channels of the image

Returns:: pointer to an allocated unsigned char array of pixels, or NULL if an error happens

Definition at line 255 of file io_png.c.

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unsigned char* io_png_read_u8_gray	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp
	)

read a PNG file into a 8bit integer array, converted to gray

See io_png_read_u8() for details.

Definition at line 310 of file io_png.c.

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unsigned char* io_png_read_u8_rgb	(	const char *	fname,
		size_t *	nxp,
		size_t *	nyp
	)

read a PNG file into a 8bit integer array, converted to RGB

See io_png_read_u8() for details.

Definition at line 268 of file io_png.c.

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static int io_png_write_abort	(	FILE *	fp,
		png_byte *	idata,
		png_bytep *	row_pointers,
		png_structp *	png_ptr_p,
		png_infop *	info_ptr_p
	)			`[static]`

internal function used to cleanup the memory when png_write_raw() fails

Parameters:

	fp	file pointer to close, ignored if NULL
	idata,row_pointers	arrays to free, ignored if NULL
	png_ptr_p,info_ptr_p,pointers	to PNG structure pointers, ignored if NULL

Returns:: -1

Definition at line 465 of file io_png.c.

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int io_png_write_f32	(	const char *	fname,
		const float *	data,
		size_t	nx,
		size_t	ny,
		size_t	nc
	)

write a float array into a PNG file

The float values are rounded to 8bit integers, and bounded to [0, 255].

Todo:: handle 16bit images and flexible min/max

Parameters:

	fname	PNG file name
	data	array to write
	nx,ny,nc	number of columns, lines and channels of the image

Returns:: 0 if everything OK, -1 if an error occured

Definition at line 669 of file io_png.c.

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static int io_png_write_raw	(	const char *	fname,
		const void *	data,
		size_t	nx,
		size_t	ny,
		size_t	nc,
		int	dtype
	)			`[static]`

internal function used to write a byte array as a PNG file

The PNG file is written as a 8bit image file, interlaced, truecolor. Depending on the number of channels, the color model is gray, gray+alpha, rgb, rgb+alpha.

Todo:: handle 16bit

Parameters:

	fname	PNG file name, "-" means stdout
	data	deinterlaced (RRR..GGG..BBB..AAA) image byte array
	nx,ny,nc	number of columns, lines and channels
	dtype	identifier for the data type to be used for output