Implements ReadImage and WriteImage functions. More...

#include <string.h>
#include <ctype.h>
#include "imageio.h"

Include dependency graph for imageio.c:

Defines
#define	FILE_BUFFER_CAPACITY (1024*4)
	Buffer size to use for BMP file I/O.
#define	ROUNDCLAMPF(x)
#define	ROUNDCLAMP(x)
Functions
int	IdentifyImageType (char Type, const char FileName)
	Identify the file type of an image file by its magic numbers.
void *	ReadImage (int Width, int Height, const char *FileName, unsigned Format)
	Read an image file as 32-bit RGBA data.
int	WriteImage (void Image, int Width, int Height, const char FileName, unsigned Format, int Quality)
	Write an image file from 8-bit RGBA image data.

Detailed Description

Implements ReadImage and WriteImage functions.

Author:: Pascal Getreuer <getreuer@gmail.com>

Two high-level functions are provided, ReadImage and WriteImage, for reading and writing image BMP, JPEG, PNG, and TIFF files. The desired format of the image data can be specified to ReadImage for how to return the data (and similarly to WriteImage for how it should interpret the data). Formatting options allow specifying the datatype of the components, conversion to grayscale, channel ordering, interleaved vs. planar, and row-major vs. column-major.

ReadImage automatically detects the format of the image being read so that the format does not need to be supplied explicitly. WriteImage infers the file format from the file extension.

Also included is a function IdentifyImageType to guess the file type (BMP, JPEG, PNG, TIFF, and a few other formats) from the file header's magic numbers without reading the image.

Support for BMP reading and writing is native: BMP reading supports 1-, 2-, 4-, 8-, 16-, 32-bit uncompressed, RLE, and bitfield images; BMP writing is limited to 24-bit uncompressed. The implementation calls libjpeg, libpng, and libtiff to handle JPEG, PNG, and TIFF images.

This program is free software: you can use, modify and/or redistribute it under the terms of the simplified BSD License. You should have received a copy of this license along this program. If not, see <http://www.opensource.org/licenses/bsd-license.html>.

Definition in file imageio.c.

Define Documentation

#define FILE_BUFFER_CAPACITY (1024*4)

Buffer size to use for BMP file I/O.

Definition at line 57 of file imageio.c.

#define ROUNDCLAMP ( x )

Value:

((x < 0.0) ? 0 : \
    ((x > 1.0) ? 255 : (uint8_t)(255.0*(x) + 0.5)))

Definition at line 61 of file imageio.c.

#define ROUNDCLAMPF ( x )

Value:

((x < 0.0f) ? 0 : \
    ((x > 1.0f) ? 255 : (uint8_t)(255.0f*(x) + 0.5f)))

Definition at line 59 of file imageio.c.

Function Documentation

int IdentifyImageType	(	char *	Type,
		const char *	FileName
	)

Identify the file type of an image file by its magic numbers.

Parameters:

Type	destination buffer with space for at least 5 chars
FileName	image file name

Returns:: 1 on successful identification, 0 on failure.

The routine fills Type with an identifying string. If there is an error or the file type is unknown, Type is set to a null string.

Definition at line 1842 of file imageio.c.

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void* ReadImage	(	int *	Width,
		int *	Height,
		const char *	FileName,
		unsigned	Format
	)

Read an image file as 32-bit RGBA data.

Parameters:

Width,Height	pointers to be filled with the image dimensions
FileName	image file name
Format	specifies the desired format for the image

Returns:: Pointer to the image data, or null on failure

The calling syntax is that the filename is the input and Width, and Height and the returned pointer are outputs. ReadImage allocates memory for the image as one contiguous block of memory and returns a pointer. It is the responsibility of the caller to call Free on this pointer when done to release this memory.

A non-null pointer indicates success. On failure, the returned pointer is null, and Width and Height are set to 0.

The Format argument is used by specifying one of the data type options

IMAGEIO_U8: unsigned 8-bit components
IMAGEIO_SINGLE: float components
IMAGEIO_DOUBLE: double components

and one of the channel options

IMAGEIO_GRAYSCALE: grayscale data
IMAGEIO_RGB: RGB color data (red is the first channel)
IMAGEIO_BGR: BGR color data (blue is the first channel)
IMAGEIO_RGBA: RGBA color+alpha data
IMAGEIO_BGRA: BGRA color+alpha data
IMAGEIO_ARGB: ARGB color+alpha data
IMAGEIO_ABGR: ABGR color+alpha data

and optionally either or both of the ordering options

IMAGEIO_PLANAR: planar order instead of interleaved components
IMAGEIO_COLUMNMAJOR: column major order instead of row major order

    uint32_t *Image;
    int Width, Height;
    
    if(!(Image = (uint32_t *)ReadImage(&Width, &Height, "myimage.bmp", 
        IMAGEIO_U8 | IMAGEIO_RGBA)))
        return 0;
    
    printf("Read image of size %dx%d\n", Width, Height);
    
    ...
    
    Free(Image);

With the default formatting IMAGEIO_U8 | IMAGEIO_RGBA, the image is organized in standard row major top-down 32-bit RGBA order. The image is organized as

    (Top left)                                             (Top right)
    Image[0]                Image[1]        ...  Image[Width-1]
    Image[Width]            Image[Width+1]  ...  Image[2*Width]
    ...                     ...             ...  ...
    Image[Width*(Height-1)] ...             ...  Image[Width*Height-1]
    (Bottom left)                                       (Bottom right)

Each element Image[k] represents one RGBA pixel, which is a 32-bit bitfield. The components of pixel Image[k] can be unpacked as

    uint8_t *Component = (uint8_t *)&Image[k];
    uint8_t Red = Component[0];
    uint8_t Green = Component[1];
    uint8_t Blue = Component[2];
    uint8_t Alpha = Component[3];

Each component is an unsigned 8-bit integer value with range 0-255. Most images do not have alpha information, in which case the alpha component is set to value 255 (full opacity).

With IMAGEIO_SINGLE or IMAGEIO_DOUBLE, the components are values in the range 0 to 1.

Definition at line 1971 of file imageio.c.

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int WriteImage	(	void *	Image,
		int	Width,
		int	Height,
		const char *	FileName,
		unsigned	Format,
		int	Quality
	)

Write an image file from 8-bit RGBA image data.

Parameters:

Image	pointer to the image data
Width,Height	image dimensions
FileName	image file name
Format	specifies how the data is formatted (see ReadImage)
Quality	the JPEG image quality (between 0 and 100)

Returns:: 1 on success, 0 on failure

The input Image should be a 32-bit RGBA image stored as in the description of ReadImage. WriteImage writes to FileName in the file format specified by its extension. If saving a JPEG image, the Quality argument specifies the quality factor (between 0 and 100). Quality has no effect on other formats.

The return value indicates success with 1 or failure with 0.

Definition at line 2074 of file imageio.c.

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imageio.c File Reference

Defines

Functions

Detailed Description

Define Documentation

Function Documentation