对lena图像分别进行4倍和16倍减采样，将256级的lena图像转换成128级灰度图像，64级灰度图像，32级灰度图像-Gray image of lena were reduced four times and 16 times sampling, 256 of 128 lena image is converted into a grayscale image, the 64-level grayscale images, 32 gray-scale image