说明：  霍夫曼编码；量化到8位字节每个像素编码及解码
(Write a MATLAB function [zipped, info] = pixel_coder(X) that takes an image X and using the Huffman coder above applied in the pixel domain quantized to 8 bits per pixel returns the coded sequence zipped along with the header information, info. You should also provide a function: X = pixel_decode(zipped,info).)