说明：  对每类中的每幅图片进行DCT变换（8*8）分块并对保留的DCT系数进行反DCT变换，得到重建的图象，显示原图像和重建图像进行对比，并计算出与原图对比的PSNR值。
(Each picture in each class is divided into DCT transform (8*8) and the reserved DCT coefficient is inverse DCT transform. The reconstructed image is obtained. The original image is compared with the reconstructed image, and the PSNR value compared with the original image is calculated.)