TV颜色空间—YUV，YIQ，YCbCr

   上述公式假定的是RGB值是根据TV编码标准进行Gamma校正之后逇值。UV分量是分别对亮度分量与红色分量、亮度分量与蓝色分量进行差值之后再赋予一定的权重：

    因此，从RGB转换为YUV的关系为：

  相应的，从YUV转换为RGB的关系为：

4.YIQ颜色空间

    原始的NTSC系统用了一种YUV的变体进行颜色编码，这种变体称之为YIQ（I for“in-phase”and Qfor “quadrature”）。IQ分量是UV分量进行旋转和镜像之后的数值：

  ß=0.576（33度）。Y分量同上述YUV颜色空间计算方式一样。

5.YCbCr颜色空

    YCbCr颜色空间是YUV颜色空间的一种变体，广泛应用于数字电视系统和图像压缩方面（比如JPEG）。色度分量Cb,Cr类似于U,V分量，也是通过亮度值与红色分量和蓝色分量差值之后，在赋予一定的权重计算得出。相比于YUV颜色空间，在RGB转换为YUV颜色空间的时候，其各个分量的权重值稍有不同。如下公式：

  相应的从YCbCr转换为RGB颜色空间为：

   BT.601中规定WR= 0.299，Wb=0.144,WG = 0.587,因此，上述公式变换为：

   YCbCr转换为RGB公式为：

    由于上述U,VI,Q,Cb,Cr可能为负数或正数，为了图像能够显示这些分量的负值，一般会在上述分量计算公式之后加上一个偏移量，使得其颜色分量为正值。比如，对于8bit表示一个分量的像素而言，其颜色分量的偏移量一般设置为128=2的7次方。

6.关键代码：

int RGB2YUV(IMAGE_TYPE *bmp_img, DWORD width, DWORD height,TYPE_YUV type) { T_U32 lineByte,Source_linebyte,source_index,dst_index; T_U16 i,j; T_U16 k = 0; T_U8 *Bmp8_img,*Source_img,R,G,B,*Y_img,*U_img,*V_img; int newbiBitCount =8,Y,U,V,I,Q,Cb,Cr; int colorTablesize; RGBQUAD colortable[256]; RGBQUAD *pColorTable1 = colortable; BITMAPFILEHEADER bf; BITMAPINFOHEADER bi; FILE *BMP2Y_fp = fopen("BMP2Y.bmp","wb"); FILE *BMP2U_fp = fopen("BMP2U.bmp","wb"); FILE *BMP2V_fp = fopen("BMP2V.bmp","wb"); if(NULL == BMP2Y_fp) { printf("Can't open BMP2Y.bmp\n"); return -1; } if(NULL == BMP2U_fp) { printf("Can't open BMP2U.bmp\n"); return -1; } if(NULL == BMP2V_fp) { printf("Can't open BMP2V.bmp\n"); return -1; } memset(&bf, 0, sizeof(bf)); memset(&bi, 0, sizeof(bi)); bf.bfType = (WORD)0x4d42; //8位图像数据每行字节数为4的倍数 lineByte = (width * newbiBitCount / 8 + 3) / 4 * 4; colorTablesize = 1024; bf.bfSize = sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+colorTablesize+lineByte*height;//图像数据加上调色板信息和前两部分BMP文件信息 bf.bfReserved1 = 0; bf.bfReserved2 = 0; bf.bfOffbits = sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+colorTablesize;//注意此offset是BMP前三部分数据，也就是真正图像数据的前面几部分之和 bi.biSize = 40; bi.biHeight = height; bi.biWidth = width; bi.biPlanes = 1; bi.biCompression = 0; bi.biBitCount = newbiBitCount;//每一个像素由8 bits表示 bi.biSizeImage = lineByte*height; bi.biXPelsPerMeter = 0; bi.biYPelsPerMter = 0; bi.biClrImportant = 0; bi.biClrUsed = 0; Source_linebyte = WIDTHBYTES(width*24); Source_img = bmp_img+54; for (i = 0; i<256; ++i) { colortable[i].rgbBlue = i; colortable[i].rgbGreen = i; colortable[i].rgbRed = i; colortable[i].rgbReserved = 0; } fwrite(&bf,sizeof(BITMAPFILEHEADER),1,BMP2Y_fp); fwrite(&bi,sizeof(BITMAPINFOHEADER),1,BMP2Y_fp); fwrite(pColorTable1, sizeof(RGBQUAD), 256, BMP2Y_fp); fwrite(&bf,sizeof(BITMAPFILEHEADER),1,BMP2U_fp); fwrite(&bi,sizeof(BITMAPINFOHEADER),1,BMP2U_fp); fwrite(pColorTable1, sizeof(RGBQUAD), 256, BMP2U_fp); fwrite(&bf,sizeof(BITMAPFILEHEADER),1,BMP2V_fp); fwrite(&bi,sizeof(BITMAPINFOHEADER),1,BMP2V_fp); fwrite(pColorTable1, sizeof(RGBQUAD), 256, BMP2V_fp); Source_img = bmp_img+54; Y_img = (T_U8*)malloc(width*height); U_img = (T_U8*)malloc(width*height); V_img = (T_U8*)malloc(width*height); if(NULL == Y_img || NULL == U_img || NULL == V_img) { printf("Can't malloc YUV_img\n"); return -1; } switch (type) { case YUV: { for (i = 0; i < height;i++) { for (j = 0;j < width;j++) { source_index = Source_linebyte*i+3*j; dst_index = lineByte*i+j; R = Source_img[source_index+2]; G = Source_img[source_index+1]; B = Source_img[source_index]; #if 0 Y = 0.299*R+0.548*G+0.114*B; U = -0.147*R-0.289*G+0.436*B+128; V = 0.615*R-0.515*G-0.100*B+128; #endif Y = (306*R+561*G+117)>>10; U = (-150*R-296*G+446*B+)>>10; V = (630*R-527*G-102*G+)>>10; Y_img[dst_index] = (T_U8)Y; U_img[dst_index] = (T_U8)U; V_img[dst_index] = (T_U8)V; } } } case YIQ: { for (i = 0; i < height;i++) { for (j = 0;j < width;j++) { source_index = Source_linebyte*i+3*j; dst_index = lineByte*i+j; R = Source_img[source_index+2]; G = Source_img[source_index+1]; B = Source_img[source_index]; #if 1 Y = 0.299*R+0.548*G+0.114*B; U = -0.147*R-0.289*G+0.436*B; V = 0.615*R-0.515*G-0.100*B; #endif #if 0 Y = (306*R+561*G+117)>>10; U = (-150*R-296*G+446*B+)>>10; V = (630*R-527*G-102*G+)>>10; #endif I =(int) (-sin(0.576)*U+V*cos(0.576))+128; Q = (int)(U*cos(0.576)+V*sin(0.576))+128; Y_img[dst_index] = (T_U8)Y; U_img[dst_index] = (T_U8)I; V_img[dst_index] = (T_U8)Q; } } } case YCBCR: { for (i = 0; i < height;i++) { for (j = 0;j < width;j++) { source_index = Source_linebyte*i+3*j; dst_index = lineByte*i+j; R = Source_img[source_index+2]; G = Source_img[source_index+1]; B = Source_img[source_index]; #if 1 Y = 0.299*R+0.587*G+0.114*B; Cb = -0.169*R-0.331*G+0.5*B+128; Cr = 0.5*R-0.419*G-0.081*B+128; #endif #if 0 Y = (306*R+601*G+117)>>10; Cb = (-173*R-339*G+512*B+)>>10; Cr = (512*R-429*G-83*G+)>>10; #endif Y_img[dst_index] = (T_U8)Y; U_img[dst_index] = (T_U8)Cb; V_img[dst_index] = (T_U8)Cr; } } } break; } fwrite(Y_img, lineByte*height, 1, BMP2Y_fp); fwrite(U_img, lineByte*height, 1, BMP2U_fp); fwrite(V_img, lineByte*height, 1, BMP2V_fp); fclose(BMP2Y_fp); fclose(BMP2U_fp); fclose(BMP2V_fp); free(Y_img); free(U_img); free(V_img); return 0; } 

7.图像效果

YUV颜色空间的Y、U、V分量