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:

本文参与腾讯云自媒体分享计划,欢迎正在阅读的你也加入,一起分享。

发表于

我来说两句

0 条评论
登录 后参与评论

扫码关注云+社区

领取腾讯云代金券