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Context-based fractional sample refinement for HEVC compliant encoding

: Maier, Georg; Bross, B.; Grois, D.; Marpe, D.; Schwarz, H.; Veltkamp, R.; Wiegand, T.

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IEEE transactions on circuits and systems for video technology 28 (2018), Nr.2, S.528-539
ISSN: 1051-8215
ISSN: 1558-2205
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IOSB ()

The H.265/MPEG-H High Efficiency Video Coding (HEVC) compliant encoding process faces the challenge of high computational complexity. Particularly, in case of inter-picture prediction, most of the computational resources are allocated for the motion estimation (ME) process. In turn, ME and motion compensation (MC) enable improving coding efficiency by addressing blocks of video frames as corresponding displacements from one or more reference blocks. These displacements do not necessarily have to be limited to integer sample positions, but may have an accuracy of half sample or quarter sample positions, which are identified during fractional sample refinement. In this work, a context-based scheme for fractional sample refinement is proposed. The scheme takes advantage of already obtained information in prior ME steps and provides significant flexibility in terms of parametrization. This way, it adaptively achieves a desired trade-off between computational complexity and coding efficiency. According to experimental results obtained for an example algorithm utilizing the proposed framework, a significant decrease in the number of search points can be achieved. For instance, considering only 6 instead of 16 fractional sample positions results in a trade-off of only 0.4% Bjøntegaard-Delta (BD)-rate loss for High Definition video sequences compared to the conventional interpolation-and-search method.