说明：  DCT1实现一维离散余弦变换； DCT2实现二维离散余弦变换； 其中使用的算法是碟形算法来实现频域变换
(DCT1 peacekeeping achieve a discrete cosine transform; DCT2 achieve two-dimensional discrete cosine transform; the use of the algorithm is dishing algorithm to achieve the transformation frequency domain)