【音视频系列2】RGB24数据格式及BMP文件格式以及存储方式

RGB24是表明图像以RGB三原色，每个像素点3个字节表示的一种图像存储格式

　　注意：在内存中RGB各分量的排列顺序为：BGR BGR BGR 

先用ffmpeg生成一个RGB24的图片，命令如下：

　　ffmpeg -i test.jpg -pix_fmt rgb24 test.rgb

生成后下面用C++代码拆分RGB24的三原色并保存：

void read_split_rgbfile(const char* file, int width, int height, int frames) {
	FILE* rgbFp = fopen(file, "rb+");
	FILE* rFp = fopen("e:\\test_r.y", "wb+");
	FILE* gFp = fopen("e:\\test_g.y", "wb+");
	FILE* bFp = fopen("e:\\test_b.y", "wb+");

	int size = width * height;
	unsigned char * buf = (unsigned char*)malloc(size * 3);
	unsigned char * rbuf = (unsigned char*)malloc(size);
	unsigned char * gbuf = (unsigned char*)malloc(size);
	unsigned char * bbuf = (unsigned char*)malloc(size);

	int ridx, gidx, bidx;
	ridx = gidx = bidx = 0;
	for (int i = 0; i < frames; i++)
	{
		fread(buf, 1, size * 3, rgbFp);
		for (int rgbidx = 0; rgbidx < size * 3; rgbidx = rgbidx + 3)
		{
			rbuf[ridx++] = buf[rgbidx];
			gbuf[gidx++] = buf[rgbidx + 1];
			bbuf[bidx++] = buf[rgbidx + 2];
		}
		fwrite(rbuf, 1, size, rFp);
		fwrite(gbuf, 1, size, gFp);
		fwrite(bbuf, 1, size, bFp);
	}
	free(buf);
	free(rbuf);
	free(gbuf);
	free(bbuf);
	fclose(rgbFp);
	fclose(rFp);
	fclose(gFp);
	fclose(bFp);
}

用YUVPlayer使用Y通道分别查看R,G,B三原色文件，如果均能显示即表示生成没有问题

　　由此可以学习RGB三原色在文件中的存储方式

 

RGB24转储为BMP文件

BMP文件格式为：

　　BMP文件头+BMP文件信息头+RGB三原色（注意：此时存储序列为BGRBGRBGR.....）

BMP文件头如下：

typedef struct tagBITMAPFILEHEADER
{
	UINT16 bfType;
	DWORD bfSize;
	UINT16 bfReserved1;
	UINT16 bfReserved2;
	DWORD bfOffBits;
} BITMAPFILEHEADER;

　　

 

BMP文件信息头如下：

　　

 

 调色板可略

使用C++代码将RGB数据转储为BMP文件代码如下：

typedef struct
{
	long imageSize;
	long blank;
	long startPos;
}BMPHead;
typedef struct {
	long length;
	long width;
	long height;
	unsigned short colorPlane;
	unsigned short bitColor;
	long zipFormat;
	long realSize;
	long xPels;
	long yPels;
	long colorUse;
	long colorImportant;
}INFOHead;
void muxer_rgb24_to_bmp(const char* rgbfile, int width, int height, const char * bmpfile) {
	FILE* rgbFp = fopen(rgbfile, "rb+");
	FILE* bmpFp = fopen(bmpfile, "wb+");
	int size = width * height;
	char bmpType[] = { 'B','M' };
	BMPHead bHead = { 0 };
	INFOHead bIHead = { 0 };
	int head_length = sizeof(bmpType) + sizeof(BMPHead) + sizeof(INFOHead);
	bHead.imageSize = size * 3 + head_length;
	bHead.startPos = head_length;

	bIHead.length = sizeof(INFOHead);
	bIHead.width = width;
	bIHead.height = -height; //注意此处的高度为负

	bIHead.colorPlane = 1;
	bIHead.bitColor = 24;
	bIHead.realSize = size * 3;
	fwrite(bmpType, 1, sizeof(bmpType), bmpFp);
	fwrite(&bHead, 1, sizeof(BMPHead), bmpFp);
	fwrite(&bIHead, 1, sizeof(INFOHead), bmpFp);

	unsigned char* rgbBuf = (unsigned char*)malloc(size * 3);
	fread(rgbBuf, 1, size * 3, rgbFp);
	for (int i=0;i <size*3;i+=3)  //调整R和B的顺序
	{
		int tmp = rgbBuf[i];
		rgbBuf[i] = rgbBuf[i + 2];
		rgbBuf[i + 2] = tmp;
	}
	fwrite(rgbBuf, 1, size * 3, bmpFp);
	free(rgbBuf);
	fclose(bmpFp);
	fclose(rgbFp);
}

 　输出文件为BMP文件，可以直接查看生成是否正确