Optimal separable adaptive loop filter

摘要

An adaptive loop filter utilizing separable filters within a quadtree-based adaptive loop filter (QALF). The filters for at least the P and B pictures are replaced with a separable filter to provide Separable QALF (SQALF). In a preferred embodiment the filter comprises a Wiener filter as a best fit approximation of the non-separable filter. In response to decoding with the SQALF approach, computational complexity in the decoder is reduced without lowering perceived visual quality. Estimation of the separable filter is obtained in the encoder by iteratively minimizing the sum of squares error with the separable filter. The SQALF filtering is described within a video decoder.

主权项

1. An apparatus, comprising:
(a) a computer configured for receiving encoded video signals; and (b) programming executable on said computer for processing said encoded video signals by performing one or more steps comprising:
(i) performing entropy decoding;(ii) reconstructing macroblocks using inverse quantization, inverse transformations, and prediction to reconstruct each macroblock;(iii) executing a deblocking filter;(iv) executing a quadtree based adaptive loop filter having separable filters for P and B pictures;(v) wherein said separable filters are separable two dimensional (2D) filters determined as a product of a one-dimensional (1D) vertical filter and a one dimensional (1D) horizontal filter;(vi) wherein said 1D horizontal filter and said 1D vertical filter are initially determined from a non-separable 2D filter, followed by iteratively minimizing error for pixels within ON regions of a quadtree structure of said quadtree based adaptive loop filter;(vii) wherein said minimizing error is performed by determining a matrix and a cross correlation that assumes said 2D separable filter is not zero phase, and performing a transposition on the 2D separable filter and cross correlation; and(viii) outputting a decoded video signal.