数字图象的数据率很大,因此在传输和存贮图象时必须考虑对图象数据加以压缩。压缩的方法主要有两大类,即预测编码法和变换编码法。变换编码法又分最佳变换和准最佳变换编码法。由于最佳变换需要计算图象的协方差矩阵及其特征向量和特征值,一般还没有快速算法,所以很难付诸实用。因而常采用准最佳变换。具有快速算法的准最佳 The data rate of the digital image is so great that it is necessary to consider compressing the image data when transferring and storing the image. Compression methods are mainly two categories, namely, predictive coding and transform coding. Transform coding method is divided into the best transformation and quasi-optimal transform coding method. Since the best transform requires calculating the covariance matrix of the image and its eigenvectors and eigenvalues, there is generally no fast algorithm, so it is hard to put it into practical use. So often use the best transformation. Quasi-optimal with fast algorithm