中文说明：读入一幅256*256图像，将它分成8*8pixel的若干块，对每块做DCT变换，保留Z型顺序的若干变换系数，进行IDCT重构图像，计算重构图像的信噪比
English Description：
Read in a 256 * 256 image, divide it into 8 * 8 pixel blocks, do DCT transform for each block, reserve some transform coefficients in z-order, reconstruct the image by IDCT, and calculate the signal-to-noise ratio of the reconstructed image