Chroma Intra Mode Coding Using Luma-Based Delta Angle Indexing
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Solution Overview
Problem
In AOMedia Video 1 (AV1), the delta angles for the chroma component are directly signaled regardless of the co-located luma prediction modes, leading to inefficiencies in video encoding and decoding processes.
Innovation Solution
Implementing a system that signals an index of delta angles for the chroma component based on the delta angles of the luma component, using predefined mapping tables and cumulative density functions to parse and encode/decode video data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If delta angles for chroma component are directly signaled, then encoding simplicity is maintained, but signaling efficiency deteriorates and redundancy increases
Solution Approach 1:
The patent introduces an index as an intermediary to represent delta angles. Instead of directly signaling the actual delta angle values, the encoder signals an index that points to predefined delta angle values stored in mapping tables at both encoder and decoder sides. This intermediary mechanism reduces the number of bits required for signaling while maintaining the ability to represent the same set of delta angle values.
Solution Approach 2:
The patent changes the parameter being signaled from the actual delta angle value to an index value. By transforming the representation from direct angle values to indirect index references, the signaling efficiency is improved. The mapping tables establish a correspondence between index values and delta angle values, allowing the decoder to reconstruct the original delta angles without receiving them directly.
2Manufacturing precision
If all delta angles are explicitly signaled, then prediction accuracy is maintained, but bitrate increases and encoding efficiency decreases
Solution Approach 1:
The patent uses copying by maintaining identical mapping tables at both the encoder and decoder sides. These tables define the relationship between index values and delta angle values. By copying the same reference data structure to both ends, the system enables lossless compression where the decoder can accurately reconstruct the original delta angles from the transmitted indices without requiring explicit signaling of each angle value.
Solution Approach 2:
Instead of signaling all delta angle values completely, the patent signals only the index values which partially represent the delta angles. The actual delta angle information is partially recovered through the predefined mapping relationship, reducing the total amount of data that needs to be transmitted while maintaining full prediction accuracy.
3Adaptability or versatility
If chroma delta angles are independently signaled, then chroma prediction independence is maintained, but context utilization is lost and efficiency decreases
Solution Approach 1:
The patent implements feedback by using the luma prediction mode as context information to determine the chroma delta angle. The encoder first determines the luma prediction mode, then uses this information to select or constrain the chroma delta angle from the mapping tables. This feedback mechanism allows the chroma component to leverage contextual information from the luma component, improving efficiency while maintaining the ability to represent independent chroma predictions when needed.
Data Source
AI summary
An example method of video decoding includes receiving a video bitstream that comprises a chroma component and a luma component. The method further includes identifying a context based on a nominal angle corresponding to the chroma component, and entropy-decoding an indicator from the video bitstream according to the context, the indicator corresponding to a delta angle for the chroma component. The method also includes decoding video data from the video bitstream using the delta angle.