Bi-Directional Optical Flow Bit-Width Control for Video Coding
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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 and correlation parameters to generate predictions with bi-directional optical flow, optimizing the coding process for video blocks.
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 significantly
Solution Approach 1:
The patent divides the current block into multiple sub-blocks and performs BIO separately for each sub-block. This segmentation allows the complex BIO computation to be distributed and managed in smaller units, reducing the overall computational burden while maintaining coding efficiency gains from BIO
Solution Approach 2:
The patent introduces a gradient threshold parameter that determines when BIO should be applied. By changing this parameter, the system can adaptively control the computational complexity of BIO - applying it only when the gradient exceeds the threshold, thus improving coding efficiency only when beneficial while reducing unnecessary computations
2Measurement precision
If gradient calculations are performed with high precision to maintain accuracy, then prediction quality is improved, but bit-width and memory requirements increase
Solution Approach 1:
The patent performs gradient calculations and BIO computations only for sub-blocks where the gradient exceeds a specified threshold. This partial action approach maintains high prediction accuracy for regions where it matters most (high gradient areas) while avoiding unnecessary high-precision computations in low-gradient regions, thus reducing overall bit-width requirements
Solution Approach 2:
The patent applies different processing strategies to different parts of the block based on local gradient characteristics. High-precision BIO is applied locally only where gradients exceed the threshold, while other regions use simpler prediction methods. This local quality approach maintains accuracy where needed while reducing overall computational and memory resources
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.