RED: _
GREEN: _
BLUE: _
Y: _
Cb: _
Cr: _ 
* RGB => YCbCr
    Y  =  0.299  * R + 0.587  * G + 0.114  * B
    Cb = -0.1687 * R - 0.3313 * G + 0.5    * B + 128
    Cr =  0.5    * R - 0.4187 * G - 0.0813 * B + 128
* YCbCr => RGB
    R = Y                        + 1.402   * (Cr - 128)
    G = Y - 0.34414 * (Cb - 128) - 0.71414 * (Cr - 128)
    B = Y + 1.772   * (Cb - 128)
ref) RGBとYCbCrの相互変換 @www.technotype.net