颜色空间变换函数。R,G,B与Y，R-Y，B-Y之间的转化、由亮度、色差变换R、G、B、c_to_sh --色差信号计算饱和度和色调-Color Space Conversion function. R, G, B and Y, RY, BY between the transformation, by the brightness, color transform R, G, B, c_to_sh calculation of color difference signal saturatio