Donghyun Kim's Paper Accepted for IEEE TCSVT Journal

Donghyun Kim's paper has been accepted for IEEE Transactions on Circuits and Systems for Video Technology (TCSVT) Journal. Congrats!

Title: Intra Prediction-Based OBMC Extension for Inter-Intra Boundaries

Authors: Donghyun Kim, Sung-Chang Lim, Jin Soo Choi, and Munchurl Kim,

Abstract:

This paper proposes a novel extension of Overlapped Block Motion Compensation (OBMC) to inter-intra boundaries in the Enhanced Compression Model (ECM), an experimental testbed developed by the Joint Video Experts Team (JVET). Conventional OBMC mitigates prediction artifacts in inter blocks by blending the base predictor with motion-compensated auxiliary predictors generated using the motion information of neighboring inter blocks, effectively alleviating spatial discontinuities at boundary transitions. However, this mechanism fundamentally relies on neighboring motion information to generate auxiliary predictors, rendering it inapplicable at inter-intra boundaries where such information is unavailable. Our analysis shows that inter-intra boundaries account for only 2.3% of the top and left boundaries of inter blocks, yet contribute 9.0% of the total coded residual energy across these boundaries.

To extend OBMC coverage to these boundaries, the proposed method introduces intra-based auxiliary predictors without additional bitstream overhead. These predictors are generated using directional intra modes implicitly derived via Decoder-side Intra Mode Derivation (DIMD) at a fine-grained 4x4 subblock level to capture local boundary characteristics. Furthermore, we propose a direct-fetch scheme for reference sample construction tailored for OBMC subblocks, which preserves boundary texture fidelity by avoiding excessive padding. 

Experimental results on ECM-14.0 demonstrate Bjøntegaard Delta Bitrate (BD-rate) performance of -0.05%/-0.13%/-0.04%/-0.06% (Y/U/V/YUV) under Random Access (RA) and -0.08%/0.13%/-0.06%/-0.05% under Low-Delay B (LDB) configurations with a negligible increase in runtime. Notably, despite this limited scope, our method enhances the coding gain of conventional Coding Unit (CU)-level OBMC in ECM-14.0 by approximately 18%. Our method demonstrated its effectiveness during JVET's exploration activities, resulting in the adoption of a low-complexity variant into ECM-15.0.