Chroma Quantization Derivation in Dual Tree Video Coding
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Solution Overview
Problem
In video encoding and decoding, the dependency of luma decoding on chroma in dual tree coding systems leads to increased bit usage and decreased coding quality, as chroma base QP is explicitly coded, which can be far from nearby luma QPs, preventing independent decoding of luma blocks.
Innovation Solution
Implicit derivation of chroma base QP from co-located luma blocks within the same picture, using functions such as average, median, or specific sample-based methods to determine the chroma QP, reducing the need for explicit coding and maintaining independent luma decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chroma base QP is explicitly coded in dual tree coding systems, then chroma quantization can be independently controlled, but bit usage increases and coding quality decreases
Solution Approach 1:
The patent uses the luma QP value as a reference (copy) to derive the chroma base QP instead of explicitly coding it. The chroma base QP is copied from the luma QP and then adjusted by an offset, eliminating the need for separate chroma QP signaling while maintaining reasonable chroma quantization control.
Solution Approach 2:
The luma QP parameter serves multiple functions: it is used for luma quantization and also serves as the basis for deriving chroma base QP. This multi-functionality reduces the need for separate chroma QP parameters, decreasing bit usage while maintaining coding efficiency.
2Adaptability or versatility
If chroma base QP is explicitly coded, then chroma quantization is independently controllable, but luma decoding becomes dependent on chroma
Solution Approach 1:
Instead of deriving luma QP from chroma base QP, the patent inverts the relationship by deriving chroma base QP from luma QP. This inversion allows luma decoding to remain independent while chroma quantization is still controllable through the derived base QP and subsequent offsets.
Solution Approach 2:
The patent separates the chroma QP control into two parts: chroma base QP (derived from luma QP for independence) and chroma QP offsets (for independent control). This segmentation allows both independence and adaptability to coexist.
3Ease of operation
If separate coding trees are used for luma and chroma, then independent processing is achieved, but chroma QP derivation becomes complex
Solution Approach 1:
The patent performs preliminary derivation of chroma base QP from luma QP before the actual chroma quantization process. This preliminary action simplifies the overall chroma QP derivation by establishing a baseline value that can be easily adjusted with offsets, reducing the complexity of separate tree processing.
Data Source
AI summary
A decoding method is disclosed. A quantization parameter of at least one luma block is obtained. The at least one luma block comprises a luma sample co-located with at least one chroma sample selected in a current chroma block. The luma and chroma blocks are coded in dual tree mode. A quantization parameter of the current chroma block is then determined responsive to the quantization parameter of the at least one luma block. Finally, the current chroma block is decoded using the quantization parameter of the current chroma block.