RGB和YCbCr颜色空间之间的转换及优化算法

RGB转换为YCbCr这个公式来自：Genesis Microchip. gm6010/gm6015 Programming Guide[M]. California US: Genesis Microchip Company, 2002:85-90|Y |    |16 |          |65.738   129.057  25.06 | |R||Cb| = |128| +  (1/256) * |-37.945  -74.494  112.43| *|G||Cr|    |128|          |112.439  -94.154  -18.28| |B|即：Y   = 0.257*R+0.564*G+0.098*B+16Cb = -0.148*R-0.291*G+0.439*B+128Cr  = 0.439*R-0.368*G-0.071*B+128YCbCr转换为RGB这个公式来自：Genesis Microchip. gm6015 Preliminary Data Sheet[M]. California US: Genesis Microchip Company, 2001:33-34|R|                   |298.082  0               408.58 |   |Y   -16  ||G| = (1/256) * |298.082  -100.291 -208.12  | * |Cb-128 ||B|                   |298.082  516.411   0           |    |Cr -128 |即：R = 1.164*(Y-16)+1.596*(Cr-128)G = 1.164*(Y-16)-0.4000392*(Cb-128)-0.813*(Cr-128)B = 1.164*(Y-16)+2.017*(Cb-128)Y：明亮度（Luminance或Luma），也就是灰阶值。“亮度”是透过RGB输入信号来建立的，方法是将RGB信号的特定部分叠加到一起。U&V：色度（Chrominance或Chroma），作用是描述影像色彩及饱和度，用于指定像素的颜色。“色度”则定义了颜色的两个方面─色调与饱和度，分别用Cr和CB来表示。Cb：反映的是RGB输入信号蓝色部分与RGB信号亮度值之间的差异。Cr：反映了RGB输入信号红色部分与RGB信号亮度值之间的差异。

RGB转为YCbCr的代码：

public static void ToYCbCr(byte* From, byte* To, int Length = 1)
{
if (Length < 1) return;
byte* End = From + Length * 3;
int Red, Green, Blue;
// int Y, Cb, Cr;
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)((YCbCrYRI * Red + YCbCrYGI * Green + YCbCrYBI * Blue + HalfShiftValue) >> Shift);
*(To + 1) = (byte)( 128 + ( (YCbCrCbRI * Red + YCbCrCbGI * Green + YCbCrCbBI * Blue + HalfShiftValue) >> Shift));
*(To + 2) = (byte) (128+( (YCbCrCrRI * Red + YCbCrCrGI * Green + YCbCrCrBI * Blue + HalfShiftValue) >> Shift));
// *To = (byte)Y;          // 不要把直接计算的代码放在这里，会降低速度，
//*(To + 1) = (byte)Cb;
//*(To + 2) = (byte)Cr;
From += 3;
To += 3;
}
}

  YCbCr转为RGB空间的代码：

        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, Cb, Cr;while (From != End){Y = *From; Cb = *(From + 1)-128; Cr = *(From + 2)-128;Red = Y + ((RGBRCrI * Cr + HalfShiftValue) >> Shift);Green = Y + ((RGBGCbI * Cb + RGBGCrI * Cr+ HalfShiftValue) >> Shift);Blue = Y + ((RGBBCbI * Cb + HalfShiftValue) >> Shift);if (Red > 255) Red = 255; else if (Red < 0) Red = 0;if (Green > 255) Green = 255; else if (Green < 0) Green = 0;    // 编译后应该比三目运算符的效率高if (Blue > 255) Blue = 255; else if (Blue < 0) Blue = 0;*To = (byte)Blue;                                               // 由于不是一一对应的，需要判断是否越界*(To + 1) = (byte)Green;*(To + 2) = (byte)Red;From += 3;To += 3;}}

参考http://www.cnblogs.com/Imageshop/archive/2013/02/14/2911309.html