A fast method and apparatus for filtering compressed images in the DCT domain

摘要

A method is described for filtering compressed images represented in the discrete-cosine-transform (DCT) domain. The filter (50) includes three sparse, vertical submatrices (V-, V++, V-+), which are sparse versions of the vertical filter components (VFCs) of a desired filter function that have been combined in such a way as to eliminate many of the non-zero elements. The filter (50) also includes three sparse, horizontal transpose submatrices (Ht-, Ht++, Ht-+), which, like the vertical submatrices, are sparse versions of the horizontal filter components of the filter function. The sparseness of these sparse submatrices yields a significant reduction in the number of computations required to filter the image in the DCT domain. To take advantage of this discovery, the input DCT data blocks are "butterflied" to retain the relationship between the input data blocks and the filtered output data blocks as a function of these sparse submatrices. The sparseness of the vertical and horizontal submatrices reduces the number of computations required to filter the image. The sparseness of the DCT data blocks can also be used to further reduce the number of computations required.