Bi-Directional Optical Flow Simplification for Video Coding Complexity
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Solution Overview
Problem
Existing video coding technologies, such as HEVC and VVC, face challenges in achieving superior coding efficiency with manageable complexity, particularly in bi-directional optical flow (BIO) processes.
Innovation Solution
Implement methods for calculating reduced-bit-width gradient arrays and motion refinements using bit shifting, generating predictions with bi-directional optical flow by summing and subtracting prediction signals, and applying interpolation filters with varying tap numbers to reduce computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bi-directional optical flow (BIO) is implemented to improve coding efficiency, then compression performance is enhanced, but computational complexity increases
Solution Approach 1:
The patent applies parameter changes by utilizing bit-shifting operations to modify the bit-width of intermediate parameters in the BIO process. Specifically, the method calculates gradient arrays with reduced bit-width (e.g., using 10-bit or 12-bit representations instead of full precision), and applies right-shift operations to intermediate results to reduce their bit-width dynamically. This allows the system to maintain coding efficiency while reducing computational complexity through parameter optimization.
Solution Approach 2:
The patent implements partial action by selectively applying reduced-bit-width calculations to specific intermediate parameters rather than all parameters throughout the BIO process. The method identifies which gradient arrays and intermediate results can be truncated to lower precision without significantly impacting final prediction accuracy, thereby reducing overall computational complexity while preserving essential coding performance.
2Measurement precision
If full-precision gradient arrays and intermediate parameters are used in BIO calculations, then prediction accuracy is improved, but memory bandwidth and computational resources increase
Solution Approach 1:
The patent changes the precision parameter of intermediate calculations by using reduced-bit-width representations for gradient arrays and intermediate results. Instead of maintaining full precision throughout the BIO process, the method strategically applies bit-truncation and right-shift operations to intermediate parameters, reducing memory bandwidth requirements while keeping final prediction accuracy acceptable through selective precision management.
3Measurement precision
If bit-depth increase is applied during BIO process to maintain precision, then calculation accuracy is improved, but implementation complexity and resource requirements increase
Solution Approach 1:
The patent applies partial bit-depth increase only where absolutely necessary to maintain calculation accuracy, rather than uniformly increasing precision throughout the entire BIO process. The method identifies specific critical calculation points where precision must be maintained and applies bit-depth increase selectively, while using reduced precision elsewhere to minimize implementation complexity.
Data Source
AI summary
Systems and methods are described for reducing the complexity of using bi-directional optical flow (BIO) in video coding. In some embodiments, bit-width reduction steps are introduced in the BIO motion refinement process to reduce the maximum bit-width used for BIO calculations. In some embodiments, simplified interpolation filters are used to generate predicted samples in an extended region around a current coding unit. In some embodiments, different interpolation filters are used for vertical versus horizontal interpolation. In some embodiments, BIO is disabled for coding units with small heights and/or for coding units that are predicted using a sub-block level inter prediction technique, such as advanced temporal motion vector prediction (ATMVP) or affine prediction.