把rgb 图像转换成yuv图像再进行图像处理。-rgb image convert to the yuv image. The Matlab function RGB() converts a color index (whole number from 1-21), English name of a color (string), or RGB triple with whole number components in {0, 1, ..., 255} into an RGB triple with real-valued components in [0,1].　RGB() allows the user to access a set of 21 colors via their common English names.　For eight of these colors that have more than one common name, the program accepts alternative names, reducing the memory burden on the user.