Bi-Directional Optical Flow Bit-Width Control for 32-Bit Decoding
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Solution Overview
Problem
Existing bi-directional optical flow (BDOF) designs in video coding, such as in Versatile Video Coding (VVC), suffer from suboptimal bit-width control of intermediate parameters, leading to unnecessary precision loss and inefficiency in motion refinement due to high-pass gradient calculations and noise sensitivity.
Innovation Solution
A method for controlling bit-widths of intermediate parameters in BDOF by introducing additional right shifts and clipping operations to optimize gradient calculations and motion refinement, ensuring the process operates within a 32-bit hardware implementation without exceeding 32 bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-pass gradient calculations are used in BDOF, then motion refinement precision is improved, but noise sensitivity increases and precision is lost due to suboptimal bit-width control
Solution Approach 1:
The patent changes the bit-width parameters of intermediate calculations in the BDOF process. Specifically, it controls the bit-width of gradient calculations and motion refinement intermediate values to prevent precision loss while avoiding noise amplification. The method adjusts parameter precision dynamically throughout the calculation chain to maintain optimal signal-to-noise ratio.
2Measurement precision
If additional right shifts and clipping operations are introduced, then bit-width control is optimized and precision is maintained, but computational complexity increases
Solution Approach 1:
The patent applies right shifts and clipping operations at predetermined stages in the BDOF calculation process. These operations are performed in advance on intermediate parameters (gradients, motion refinements) to control their bit-width before they propagate through subsequent calculations. This preliminary control prevents precision loss accumulation without requiring complex dynamic adjustment mechanisms.
3Productivity
If 32-bit hardware implementation is utilized, then processing efficiency is improved, but bit-width overflow may occur without proper control
Solution Approach 1:
The patent implements dynamic bit-width control throughout the BDOF calculation chain. Each intermediate parameter (horizontal gradients, vertical gradients, sample differences, motion refinements) has its bit-width adjusted according to its specific role in the calculation. This dynamic control ensures that no intermediate value exceeds 32 bits while maximizing the utilization of available hardware precision for optimal processing efficiency.
Data Source
AI summary
The present disclosure relates to a bit-width control method of bi-directional optical flow (BDOF) for decoding a video signal. The method includes obtaining a first reference picture and a second reference picture associated with a 4×4 video sub-block; obtaining first prediction samples I(0) for samples in the 4×4 video sub-block from the first reference picture; obtaining second prediction samples I(1) for the samples in the 4×4 video sub-block from the second reference picture; obtaining motion refinements for the samples in the 4×4 video sub-block based on a 6×6 window applied to the 4×4 video sub-block, by controlling bit-widths of intermediate parameters; and obtaining bi-prediction samples of the samples in the 4×4 video sub-block based on the motion refinements.