Chroma-From-Luma Scaling for Accurate Intra Prediction
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Solution Overview
Problem
Existing video coding technologies, such as AV1 and HEVC, do not effectively exploit the correlation between neighboring samples of different color components for chroma intra prediction, leading to inefficiencies in decoding complexity and prediction accuracy.
Innovation Solution
A method for cross-component intra prediction that derives a predicted scaling factor based on neighboring samples of a luma block to improve chroma block reconstruction, using a linear model and least mean square method to determine the scaling parameter for chroma from luma (CfL) intra prediction mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing video coding technologies (AV1, HEVC) are used for chroma intra prediction, then decoding can be performed, but prediction accuracy is insufficient and decoder complexity is high
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing scaling factors for different chroma prediction modes before actual decoding occurs. The encoder computes these scaling factors based on neighboring luma samples and stores them in a lookup table, so that during decoding the processor can simply retrieve the appropriate scaling factor without performing complex real-time calculations, thus reducing decoder complexity while maintaining high prediction accuracy
Solution Approach 2:
The patent implements self-service by enabling the decoder to autonomously determine the correct scaling factor by examining the intra prediction mode index and neighboring sample values, without requiring external intervention or complex control logic. The decoder uses the stored scaling factor table and simple lookup mechanisms to self-determine the appropriate scaling parameters for different chroma prediction modes, reducing the need for complex decoder architecture
2Measurement precision
If scaling parameters are not optimized for chroma from luma prediction, then decoding is simpler, but prediction accuracy deteriorates
Solution Approach 1:
The patent applies parameter changes by introducing a scaling factor parameter that varies based on the intra prediction mode and neighboring sample values. Instead of using a fixed scaling parameter for all chroma prediction modes, the system dynamically adjusts the scaling factor according to the specific prediction mode (e.g., DC, AC, directional modes) and the characteristics of neighboring luma samples, thereby improving prediction accuracy without excessive signaling overhead
Solution Approach 2:
The patent uses preliminary action by pre-computing and storing scaling factors for different prediction modes in a lookup table during encoder operation. This allows the decoder to retrieve the appropriate scaling factor through simple table lookup based on the prediction mode index and neighboring sample values, avoiding complex real-time parameter calculation while maintaining optimized prediction accuracy
Data Source
AI summary
Methods and apparatuses for performing cross-component intra prediction, including: receiving a current chroma block from a coded bitstream; determining, from the coded bitstream, that a scaling factor used for the current chroma block in a chroma for luma (CfL) intra prediction mode; deriving a predicted scaling factor based on first neighboring samples of the current chroma block and second neighboring samples of a luma block that is co-located with the current chroma block; using the predicted scaling factor as the scaling factor used for the current chroma block in the CfL intra prediction mode; reconstructing the current chroma block after scaling the current chroma block based on the predicted scaling factor.