单层小波变换对二维图像进行分解,[cA1,cH1,cV1,cD1]=dwt2(X, db1 ):计算图像X指定小波基的单层二维离散小波变换分解，其中cA为近似小波系数矩阵，参量cH,cV和cD分别为小波分解的水平细节系数、垂直细节系数和对角细节系数。-Single layer wavelet transform to the two-dimensional image decomposition, [cA1, cH1, cV1, cD1]=dwt2 (X, db1 ): X single image specified calculation of two-dimensional discrete wavelet transform wavelet decomposition, where cA is the approximation of wavelet coefficient matrix, parameters of cH, cV and cD respectively the level of detail coefficients, wavelet decomposition and vertical detail coefficients the diagonal detail coefficients.