LIC Flag Inheritance for Affine Video Coding Efficiency
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Solution Overview
Problem
The application of Local Illumination Compensation (LIC) on affine coded blocks in video compression is not optimal for coding efficiency, particularly when the current block is coded with constructed affine merge mode, and the LIC flag is explicitly signaled, leading to additional signaling costs.
Innovation Solution
A method that determines whether LIC is applicable for a current data block by checking if it is coded with affine inter prediction, and if applicable, infers or inherits an LIC flag from a neighboring block, using it to generate a prediction with a derived motion vector, applying LIC based on a linear model for illumination changes, and adjusting scaling factors and offsets using neighboring and reference samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LIC flag is explicitly signaled for affine coded blocks, then prediction accuracy is improved, but signaling cost increases
Solution Approach 1:
The patent extracts the LIC flag signaling from the general affine mode syntax and creates a separate, optional syntax element that is only present when LIC is actually used. This removes the unnecessary signaling overhead for blocks that don't require LIC while preserving the ability to signal when needed.
Solution Approach 2:
Instead of explicitly signaling LIC flag for all affine blocks (which increases signaling cost), the patent inverts the approach by using implicit inheritance from neighboring blocks. The LIC is only explicitly signaled when it differs from the inherited value, reducing redundant signaling while maintaining prediction accuracy where needed.
2Measurement precision
If LIC is applied to all affine coded blocks, then prediction accuracy is improved, but coding complexity increases
Solution Approach 1:
The patent applies LIC selectively to specific affine coded blocks where it is actually beneficial, rather than uniformly to all affine blocks. The decision to apply LIC is made based on local characteristics of each block and its neighbors, optimizing the balance between prediction accuracy and coding complexity.
Solution Approach 2:
Instead of applying LIC to all affine blocks (excessive action), the patent applies LIC only to the subset of blocks where it provides measurable improvement (partial action). This is achieved through conditional syntax elements that enable LIC only when needed, reducing overall coding complexity while maintaining accuracy where required.
3Loss of information
If LIC flag is inherited from neighboring blocks, then signaling cost is reduced, but adaptability decreases
Solution Approach 1:
The patent creates a dynamic system where the LIC flag can be either inherited from neighboring blocks or explicitly signaled, depending on the specific block characteristics. This dynamic approach allows the encoder to adapt to local conditions, maintaining LIC adaptability while reducing signaling cost through intelligent inheritance where appropriate.
Solution Approach 2:
The patent implements a feedback mechanism where the encoder evaluates whether explicit LIC signaling is needed based on the difference between the current block's optimal LIC setting and the inherited value from neighbors. This feedback loop ensures adaptability is maintained by explicitly signaling only when necessary, while reducing signaling cost through inheritance when the inherited value is sufficient.
Data Source
AI summary
A method may include: receiving information regarding a current data block of an image; determining whether Local Illumination Compensation (LIC) is applicable for the current data block; based on determining that the LIC is applicable for the current data block, at least one of: infering an LIC flag for the current data block to be 1 or true corresponding to the LIC being enabled, or inheriting the current block's LIC flag from an LIC flag of a neighboring block; and based on the LIC flag for the current data block corresponding to the LIC being enabled, generate a prediction of at least one sub-block with a derived motion vector by applying LIC to the current data block using the inherited LIC flag.