说明：  RGB转换到YUV4:2:2,4:2:0的程序. 需要把RGB图片放到C:\\目录下. 在这里YUV是 先write所有的Y,然后写所有的U,最后写所有的V.
(RGB to YUV4 : 2:2,4:2:0 procedures. Need RGB images into C : \ \ directory. YUV here is first of all write Y and then write all the U, Finally write all the V.)