Implements ReadImage and WriteImage functions. More...

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

Macros
#define	FILE_BUFFER_CAPACITY (1024*4)
	Buffer size to use for BMP file I/O.

#define	ROUNDCLAMPF(x)

#define	ROUNDCLAMP(x)

Functions
static int	StringEndsWith (const char String, const char Suffix)
	Case-insensitive test to see if String ends with Suffix.

static void	FillImage (uint32_t *Image, int Width, int Height, uint32_t Color)
	Fill an image with a color.

static uint32_t *	GetImagePalette (int NumColors, int UseColor, int UseAlpha, const uint32_t Image, int Width, int Height)
	Check use of color and alpha, and count number of distinct colors. More...

static uint16_t	ReadWordLE (FILE *File)
	Read a 16-bit little Endian word from File.

static uint32_t	ReadDWordLE (FILE *File)
	Read a 32-bit little Endian double word from File.

static void	WriteWordLE (uint16_t w, FILE *File)
	Write a 16-bit word in little Endian format.

static void	WriteDWordLE (uint32_t dw, FILE *File)
	Write a 32-bit double word in little Endian format.

static int	ReadBmp1Bit (uint32_t Image, int Width, int Height, FILE File, const uint32_t *Palette)
	Internal function for reading 1-bit BMP.

static int	ReadBmp4Bit (uint32_t Image, int Width, int Height, FILE File, const uint32_t *Palette)
	Internal function for reading 4-bit BMP.

static int	ReadBmp4BitRle (uint32_t Image, int Width, int Height, FILE File, const uint32_t *Palette)
	Internal function for reading 4-bit RLE-compressed BMP.

static int	ReadBmp8Bit (uint32_t Image, int Width, int Height, FILE File, const uint32_t *Palette)
	Internal function for reading 8-bit BMP.

static int	ReadBmp8BitRle (uint32_t Image, int Width, int Height, FILE File, const uint32_t *Palette)
	Internal function for reading 8-bit RLE-compressed BMP.

static int	ReadBmp24Bit (uint32_t Image, int Width, int Height, FILE File)
	Internal function for reading 24-bit BMP.

static void	GetMaskShifts (uint32_t Mask, int LeftShift, int RightShift)
	Internal function for determining bit shifts in bitfield BMP.

static int	ReadBmp16Bit (uint32_t Image, int Width, int Height, FILE File, uint32_t RedMask, uint32_t GreenMask, uint32_t BlueMask, uint32_t AlphaMask)
	Internal function for reading 16-bit BMP.

static int	ReadBmp32Bit (uint32_t Image, int Width, int Height, FILE File, uint32_t RedMask, uint32_t GreenMask, uint32_t BlueMask, uint32_t AlphaMask)
	Internal function for reading 32-bit BMP.

static int	ReadBmp (uint32_t *Image, int Width, int Height, FILE File)
	Read a BMP (Windows Bitmap) image file as RGBA data. More...

static int	WriteBmp (const uint32_t Image, int Width, int Height, FILE File)
	Write a BMP image. More...

static void *	ConvertToFormat (uint32_t *Src, int Width, int Height, unsigned Format)
	Convert from RGBA U8 to a specified format.

static uint32_t *	ConvertFromFormat (void *Src, int Width, int Height, unsigned Format)
	Convert from a specified format to RGBA U8.

int	IdentifyImageType (char Type, const char FileName)
	Identify the file type of an image file by its magic numbers. More...

void *	ReadImage (int Width, int Height, const char *FileName, unsigned Format)
	Read an image file as 32-bit RGBA data. More...

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. More...

Detailed Description

Implements ReadImage and WriteImage functions.

Author: Pascal Getreuer getre.nosp@m.uer@.nosp@m.gmail.nosp@m..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.

Macro Definition Documentation

#define ROUNDCLAMP ( x )

Value:

((x < 0.0) ? 0 : \

((x > 1.0) ? 255 : (uint8_t)(255.0*(x) + 0.5)))

Definition at line 62 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 60 of file imageio.c.

Function Documentation

static uint32_t* GetImagePalette	(	int *	NumColors,
		int *	UseColor,
		int *	UseAlpha,
		const uint32_t *	Image,
		int	Width,
		int	Height
	)

static

Check use of color and alpha, and count number of distinct colors.

Parameters

NumColors	set by the routine to the number of unique colors
UseColor	set to 1 if the image is not grayscale
UseAlpha	set to 1 if the image alpha is not constant 255
Image	pointer to U8 RGBA interleaved image data
Width,Height	dimensions of the image

Returns: pointer to a color palette with NumColors entries or NULL if the number of distinct colors exceeds 256.

This routine checks whether an RGBA image makes use of color and alpha, and constructs a palette if the number of distinct colors is 256 or fewer. This information is useful for writing image files with smaller file size.

Definition at line 110 of file imageio.c.

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 1844 of file imageio.c.

static int ReadBmp	(	uint32_t **	Image,
		int *	Width,
		int *	Height,
		FILE *	File
	)

static

Read a BMP (Windows Bitmap) image file as RGBA data.

Parameters

Image,Width,Height	pointers to be filled with the pointer to the image data and the image dimensions.
File	stdio FILE pointer pointing to the beginning of the BMP file

Returns: 1 on success, 0 on failure

This function is called by ReadImage to read BMP images. Before calling ReadBmp, the caller should open File as a FILE pointer in binary read mode. When ReadBmp is complete, the caller should close File.

Definition at line 632 of file imageio.c.

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 1973 of file imageio.c.

static int WriteBmp	(	const uint32_t *	Image,
		int	Width,
		int	Height,
		FILE *	File
	)

static

Write a BMP image.

Parameters

Image	pointer to RGBA image data
Width,Height	the image dimensions
File	stdio FILE pointer

Returns: 1 on success, 0 on failure

This function is called by WriteImage to write BMP images. The caller should open File in binary write mode. When WriteBmp is complete, the caller should close File.

The image is generally saved in uncompressed 24-bit RGB format. But where possible, the image is saved using an 8-bit palette for a substantial decrease in file size. The image data is always saved losslessly.

Note: The alpha channel is lost when saving to BMP. It is possible to write the alpha channel in a 32-bit BMP image, however, such images are not widely supported. RGB 24-bit BMP on the other hand is well supported.

Definition at line 828 of file imageio.c.

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 2076 of file imageio.c.

Macros

Functions

Detailed Description

Macro Definition Documentation

Function Documentation