On the adaptive selection of partitioning tree types for coding video color channels

We explore the use of separate partitioning structures for luma and chroma channels in the design of next generation video codecs. The proposed methods are evaluated relative to the Quad-Tree, Ternary-Tree and Binary-Tree (QTTTBT) partitioning framework currently implemented in the BenchMark Set (BMS-1.0) software being used in the development of the Versatile Video Coding (VVC) project. VVC is the next generation video compression standard under development by the Joint Video Experts Team (JVET), which is joint collaboration between MPEG and the ITU-T. In the paper, the performance of using shared or separate partitioning tree structures for luma and chroma channels is measured for sequences including those used for the Joint Call for Proposals on video compression with capability beyond HEVC issued by MPEG/ITU-T and trends are analyzed. The use of separate partitioning tree structures is restricted to intra coded regions. Objective performance is reported using the Bjontegaard Delta (BD) bitrate, and visual observations are also provided. To demonstrate the efficacy of using different partition structures, bitrate savings are computed using simulations and show an average improvement of 0.46%(Y)/7.83%(Cb)/7.96%(Cr) relative to state-of-the-art. It is asserted that the coding efficiency improvement is especially pronounced in sequences with occlusions/emergence of objects or dynamic changing content (e.g. fire, water, smoke). In the tests conducted, the Campfire sequence which has a large portion of the picture exhibiting a burning fire, shows the most BD bitrate saving of 1.79%(Y)/5.45%(Cb)/1.82%(Cr).