Bitmap备忘

这是一篇阅读Bitmap相关内容的笔记！
程序运行环境：

BMP图像文件被分成4个部分：位图文件头(Bitmap File Header)、位图信息头(Bitmap Info Header)、颜色表(Color Map)和位图数据(即图像数据，Data Bits或Data Body)。

这本书(http://vipbase.net/ipbook/chap01.htm)第一章节有讲这些。

biBitCount：每个像素所占的位数(bit)，其值必须为1(黑白图像)、4(16色图)、8(256色)、24(真彩色图)，32(带透明度alpha通道，位于前8位)。

以下这几篇博客有讲些基本的东西。
http://www.cnblogs.com/shengansong/archive/2011/09/23/2186409.html
http://blog.csdn.net/yutianzuijin/article/details/8243343
http://blog.csdn.net/scut1135/article/details/5573395

我有参考以上资料修改出一个可以在x86_64 GNU/Linux编译并运行的程序，注释里面有写些需要注意的地方。

	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	// for Linux platform, plz make sure the size of data type is correct for BMP spec.
	// if you use this on Windows or other platforms, plz pay attention to this.
	typedef int LONG;
	typedef unsigned char BYTE;
	typedef unsigned int DWORD;
	typedef unsigned short WORD;
	// __attribute__((packed)) on non-Intel arch may cause some unexpected error, plz be informed.
	typedef struct tagBITMAPFILEHEADER
	{
	WORD bfType; // 2 /* Magic identifier */
	DWORD bfSize; // 4 /* File size in bytes */
	WORD bfReserved1; // 2
	WORD bfReserved2; // 2
	DWORD bfOffBits; // 4 /* Offset to image data, bytes */
	} __attribute__((packed)) BITMAPFILEHEADER;
	typedef struct tagBITMAPINFOHEADER
	{
	DWORD biSize; // 4 /* Header size in bytes */
	LONG biWidth; // 4 /* Width of image */
	LONG biHeight; // 4 /* Height of image */
	WORD biPlanes; // 2 /* Number of colour planes */
	WORD biBitCount; // 2 /* Bits per pixel */
	DWORD biCompress; // 4 /* Compression type */
	DWORD biSizeImage; // 4 /* Image size in bytes */
	LONG biXPelsPerMeter; // 4
	LONG biYPelsPerMeter; // 4 /* Pixels per meter */
	DWORD biClrUsed; // 4 /* Number of colours */
	DWORD biClrImportant; // 4 /* Important colours */
	} __attribute__((packed)) BITMAPINFOHEADER;
	/*
	typedef struct tagRGBQUAD
	{
	unsigned char rgbBlue;
	unsigned char rgbGreen;
	unsigned char rgbRed;
	unsigned char rgbReserved;
	} RGBQUAD;
	* for biBitCount is 16/24/32, it may be useless
	*/
	typedef struct
	{
	BYTE b;
	BYTE g;
	BYTE r;
	} RGB_data; // RGB TYPE, plz also make sure the order
	int bmp_generator(char *filename, int width, int height, unsigned char *data)
	{
	BITMAPFILEHEADER bmp_head;
	BITMAPINFOHEADER bmp_info;
	int size = width * height * 3;
	bmp_head.bfType = 0x4D42; // 'BM'
	bmp_head.bfSize= size + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER); // 24 + head + info no quad
	bmp_head.bfReserved1 = bmp_head.bfReserved2 = 0;
	bmp_head.bfOffBits = bmp_head.bfSize - size;
	// finish the initial of head
	bmp_info.biSize = 40;
	bmp_info.biWidth = width;
	bmp_info.biHeight = height;
	bmp_info.biPlanes = 1;
	bmp_info.biBitCount = 24; // bit(s) per pixel, 24 is true color
	bmp_info.biCompress = 0;
	bmp_info.biSizeImage = size;
	bmp_info.biXPelsPerMeter = 0;
	bmp_info.biYPelsPerMeter = 0;
	bmp_info.biClrUsed = 0 ;
	bmp_info.biClrImportant = 0;
	// finish the initial of infohead;
	// copy the data
	FILE *fp;
	if (!(fp = fopen(filename,"wb"))) return 0;
	fwrite(&bmp_head, 1, sizeof(BITMAPFILEHEADER), fp);
	fwrite(&bmp_info, 1, sizeof(BITMAPINFOHEADER), fp);
	fwrite(data, 1, size, fp);
	fclose(fp);
	return 1;
	}
	int main(int argc, char **argv)
	{
	int i,j;
	RGB_data buffer[512][512];
	memset(buffer, 0, sizeof(buffer));
	for (i = 0; i < 256; i++)
	{
	for (j = 0; j < 256; j++)
	{
	buffer[i][j].g = buffer[i][j].b = 0x07;
	buffer[i][j].r = 0xff;
	}
	}
	bmp_generator("./test.bmp", 512, 512, (BYTE*)buffer);
	return EXIT_SUCCESS;
	}

view raw bitmap_gen_test.c hosted with by GitHub

some pitfalls of __attribute__((packed)), plz refer
http://stackoverflow.com/questions/8568432/is-gccs-attribute-packed-pragma-pack-unsafe
http://stackoverflow.com/questions/11770451/what-is-the-meaning-of-attribute-packed-aligned4
http://stackoverflow.com/questions/11667181/why-does-padding-have-to-be-a-power-of-two
http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member
http://en.wikipedia.org/wiki/Data_structure_alignment

Linux下BMP转化为JPEG程序源代码
http://www.linuxidc.com/Linux/2011-03/33193.htm

如果你自己要开发JPEG相关的话，确保这些包是有安装的。