IntraBC Prediction Using Shared CABAC Context and Non-Square Partitions
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Solution Overview
Problem
Current Intra-block copy (IntraBC) coding modes in video compression, particularly for screen content coding in HEVC, face limitations in prediction efficiency and complexity due to restricted motion vectors and binarization methods, which hinder optimal coding performance.
Innovation Solution
The proposed solution involves improvements to IntraBC prediction by using context-adaptive binary arithmetic coding (CABAC) for signaling partition modes, allowing shared or independent context modeling between IntraBC and Inter prediction, and enabling non-square partitioning, along with deriving chroma displacement vectors from luma vectors, to enhance coding efficiency and simplify the prediction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If IntraBC mode uses restricted motion vectors (1-D only) and fixed-length binarization, then device complexity is reduced, but coding efficiency deteriorates
Solution Approach 1:
The patent transitions from static 1-D motion vector restrictions to dynamic 2-D motion vector support, allowing the system to adaptively select between horizontal-only, vertical-only, or combined 2-D motion compensation based on the actual screen content characteristics, thereby improving coding efficiency while maintaining manageable complexity
Solution Approach 2:
The patent changes the binarization parameter from fixed-length to variable-length exponential-Golomb coding, and modifies the motion vector dimensionality parameter from 1-D to 2-D, enabling more flexible and efficient representation of motion information in screen content video
2Reliability
If IntraBC mode uses separate context modeling from Inter prediction, then reliability of IntraBC coding is improved, but device complexity increases
Solution Approach 1:
The patent makes the context modeling mechanism universal by allowing IntraBC to share the same CABAC context structures and binarization processes used in Inter prediction, enabling a single context modeling system to serve both intra and inter prediction modes without requiring separate dedicated models, thus reducing complexity while maintaining coding reliability
3Ease of manufacture
If IntraBC mode uses square partitioning only, then ease of manufacture is improved, but adaptability deteriorates
Solution Approach 1:
The patent segments the coding unit into non-square prediction units with aspect ratios of 2:1 or 1:2, allowing flexible partitioning that adapts to the directional characteristics of screen content such as text lines or graphical edges, thereby improving coding efficiency for various content patterns while maintaining straightforward implementation through standardized partition ratios
Data Source
AI summary
A method of signaling of coding modes including an IntraBC mode (Intra-block copy mode) to improve the coding efficiency is disclosed. In one embodiment, the partition mode associated with IntraBC mode and the corresponding partition mode for Inter mode use the same binarization process and the same context modelling. In another embodiment, the displacement vector of IntraBC prediction for the chroma block is derived from the displacement vectors of the corresponding luma block. In yet another embodiment, a non-square PU is partitioned into multiple TUs (transform units) and IntraBC prediction is performed TU by TU.