对比度保留的彩色图像去色算法，可用于灰度打印等场合，比通用的RGB2YUV，性能好很多。-The Code is created based on the method described in the following paper "Contrast Preserving Decolorization", Cewu Lu, Li Xu, Jiaya Jia, IEEE International Conference on Computational Photography (ICCP),