颜色空间系列4: RGB和YDbDr颜色空间的转换及优化算法
颜色空间系列4: RGB和YDbDr颜色空间的转换及优化算法
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颜色空间系列4: RGB和YDbDr颜色空间的转换及优化算法
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    颜色空间系列代码下载链接:http://files.cnblogs.com/Imageshop/ImageInfo.rar (同文章同步更新)

    YDbDr颜色空间和YCbCr颜色空间类似,其和RGB空间之间的相互转换公式里取http://en.wikipedia.org/wiki/YDbDr 所描述的。

     RGB转为YDbDr为:

                             (1)

      对应的YDbDr转换为RGB的公式为:

                       (2)

     由式(1)可知Y的范围是[0,255],Db的范围是[-1.333*255,1.333*255],Dr的范围亦为[-1.333*255,1.333*255]。

     为了使Db,Dr的变换量程也为255-0大小,需要将上述Db/Dr压缩1.333*2倍,即将各系数处理( 1.333*2),得到新的转换: 

   [Y  ]     [0.2990  -0.1688   -0.5000 ]    [R]
     [Db] =   [0.5870     -0.3312    0.4186  ]    [G]      
   [Dr]     [0.1140     0.5000     0.0814   ]    [B]

     对应的逆变换可用matlab求上述矩阵的逆阵即可:

   [R]     [ 1.000000000000000   0.000246081707249  -1.402083073344533 ]    [Y]
     [G] =   [ 1.000000000000000  -0.344268308442098   0.714219609001458 ]    [Db]      
   [B]     [ 1.000000000000000   1.772034373903893  -0.000211153981059 ]    [Dr]

      理论上 YDbDr和RGB之间的转换时完全无损可逆的。不过如果YDbDr采用byte类型表达会有一定的精度损失。

      附上最终的代码供大家参考:

sealed unsafe class RGBYDbDr { //const float YDbDrYRF = 0.299F; // RGB转YDbDr的系数(浮点类型) //const float YDbDrYGF = 0.587F; //const float YDbDrYBF = 0.114F; //const float YDbDrDbRF = -0.450F; //const float YDbDrDbGF = -0.883F; //const float YDbDrDbBF = 1.333F; //const float YDbDrDrRF = -1.333F; //const float YDbDrDrGF = 1.116F; //const float YDbDrDrBF = 0.217F; //const float RGBRYF = 1.00000F; // YDbDr转RGB的系数(浮点类型) //const float RGBRDbF = 0.000092303716148F; //const float RGBRDrF = -0.525912630661865F; //const float RGBGYF = 1.00000F; //const float RGBGDbF = -0.129132898890509F; //const float RGBGDrF = 0.267899328207599F; //const float RGBBYF = 1.00000F; //const float RGBBDbF = 0.664679059978955F; //const float RGBBDrF = -0.000079202543533F;


        const float YDbDrYRF = 0.299F;              // RGB转YDbDr的系数(浮点类型)
        const float YDbDrYGF = 0.587F; const float YDbDrYBF = 0.114F; const float YDbDrDbRF = -0.1688F; const float YDbDrDbGF = -0.3312F; const float YDbDrDbBF = 0.5F; const float YDbDrDrRF = -0.5F; const float YDbDrDrGF = 0.4186F; const float YDbDrDrBF = 0.0814F; const float RGBRYF = 1.00000F;            // YDbDr转RGB的系数(浮点类型)
        const float RGBRDbF = 0.0002460817072494899F; const float RGBRDrF = -1.402083073344533F; const float RGBGYF = 1.00000F; const float RGBGDbF = -0.344268308442098F; const float RGBGDrF = 0.714219609001458F; const float RGBBYF = 1.00000F; const float RGBBDbF = 1.772034373903893F; const float RGBBDrF = 0.0002111539810593343F; const int Shift = 20; const int HalfShiftValue = 1 << (Shift - 1); const int YDbDrYRI = (int)(YDbDrYRF * (1 << Shift) + 0.5);         // RGB转YDbDr的系数(整数类型)
        const int YDbDrYGI = (int)(YDbDrYGF * (1 << Shift) + 0.5); const int YDbDrYBI = (int)(YDbDrYBF * (1 << Shift) + 0.5); const int YDbDrDbRI = (int)(YDbDrDbRF * (1 << Shift) + 0.5); const int YDbDrDbGI = (int)(YDbDrDbGF * (1 << Shift) + 0.5); const int YDbDrDbBI = (int)(YDbDrDbBF * (1 << Shift) + 0.5); const int YDbDrDrRI = (int)(YDbDrDrRF * (1 << Shift) + 0.5); const int YDbDrDrGI = (int)(YDbDrDrGF * (1 << Shift) + 0.5); const int YDbDrDrBI = (int)(YDbDrDrBF * (1 << Shift) + 0.5); const int RGBRYI = (int)(RGBRYF * (1 << Shift) + 0.5);              // YDbDr转RGB的系数(整数类型)
        const int RGBRDbI = (int)(RGBRDbF * (1 << Shift) + 0.5); const int RGBRDrI = (int)(RGBRDrF * (1 << Shift) + 0.5); const int RGBGYI = (int)(RGBGYF * (1 << Shift) + 0.5); const int RGBGDbI = (int)(RGBGDbF * (1 << Shift) + 0.5); const int RGBGDrI = (int)(RGBGDrF * (1 << Shift) + 0.5); const int RGBBYI = (int)(RGBBYF * (1 << Shift) + 0.5); const int RGBBDbI = (int)(RGBBDbF * (1 << Shift) + 0.5); const int RGBBDrI = (int)(RGBBDrF * (1 << Shift) + 0.5); public static void ToYDbDr(byte* From, byte* To, int Length = 1) { if (Length < 1) return; byte* End = From + Length * 3; int Red, Green, Blue; while (From != End) { Blue = *From; Green = *(From + 1); Red = *(From + 2); // 无需判断是否存在溢出,因为测试过整个RGB空间的所有颜色值,无颜色存在溢出
                *To = (byte)((YDbDrYRI * Red + YDbDrYGI * Green + YDbDrYBI * Blue + HalfShiftValue) >> Shift);         // YDbDr和YUV的Y相同
                *(To + 1) = (byte)(128 + ((YDbDrDbRI * Red + YDbDrDbGI * Green + YDbDrDbBI * Blue + HalfShiftValue) >> Shift)); *(To + 2) = (byte)(128 + ((YDbDrDrRI * Red + YDbDrDrGI * Green + YDbDrDrBI * Blue + HalfShiftValue) >> Shift)); From += 3; To += 3; } } public static void ToRGB(byte* From, byte* To, int Length = 1) { if (Length < 1) return; byte* End = From + Length * 3; int Red, Green, Blue; int Y, Db, Dr; while (From != End) { Y = *From; Db = *(From + 1) - 128; Dr = *(From + 2) - 128; Red = Y + ((RGBRDbI * Db + RGBRDrI * Dr + HalfShiftValue) >> Shift); Green = Y + ((RGBGDbI * Db + RGBGDrI * Dr + HalfShiftValue) >> Shift); Blue = Y + ((RGBBDbI * Db + RGBBDrI * Dr + HalfShiftValue) >> Shift); if (Red > 255) Red = 255; else if (Red < 0) Red = 0; if (Green > 255) Green = 255; else if (Green < 0) Green = 0; if (Blue > 255) Blue = 255; else if (Blue < 0) Blue = 0; *To = (byte)Blue; *(To + 1) = (byte)Green; *(To + 2) = (byte)Red; From += 3; To += 3; } } }

  由于有些转换系数很小,建议Shift 常数取值不得小于10,否则会有更多的损失。

     照例附上一些效果:

     原图:

    

    YDbDr综合效果图:

    

    Y通道图:

    

    Db通道:

    

    Dr通道:

    

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