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Parallelized deblocking filter for hybrid video coding

State of the art hybrid video coding algorithms, e.g. H.264 / MPEG-4 AVC [1] and the currently emerging HEVC video coding standard [2], apply block-based prediction and subsequent block-based prediction error coding, which includes quantization. To reduce annoying block artifacts typically resulting from the combination of block-based processing and coarse quantization, adaptive deblocking filters [3] are applied. In H.264 / MPEG-4 AVC as well as in HEVC, all vertical edges of a current block are deblocked before all horizontal edges. For each edge, it is decided whether to filter or not. If filtering is decided it is applied subsequently. The result of each filtering step is used as an input to all subsequent decision and filter operations. This paper consists of three parts. First, an implementation of the HEVC deblocking filter is presented exploiting parallel processing capabilities, which is important for today's hard- and software implementations. Second, an analysis of this implementation is performed having the result that the critical path consists of 42 sequential operations. In order to shorten the critical path, the parallel processing capabilities are increased in the third part of this paper. This is achieved by dissolving dependencies between consecutive decision and filter operations. The dissolved dependencies enable a shorter critical path of 30 sequential operations, which is a reduction of 30%. Experiments show that the coding efficiency stays unchanged with respect to both, subjective and objective quality. As a consequence of the achieved implementation benefits this technique has been adopted into the HEVC working draft.