对girl图像做二维DCT，并通过对变换后的某些系数置零达到压缩目的-Girl doing two-dimensional images of the DCT, and through certain coefficients transformed to achieve compression purpose of nulling

dct2的编程实现，用来压缩灰度图像，需要修改输入的图像名，保持和程序里的名称一致-dct2' s programming is used to compress grayscale images, need to modify the input image name, the name of maintaining and procedures where the same