Chroma QP Extension and Mapping for Luma-Aligned Bit Allocation
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Solution Overview
Problem
Existing video codec standards, such as HEVC, limit the maximum quantization parameter (QP) for chroma components, leading to inefficient bit allocation and reduced overall video quality, especially in low bit-rate applications.
Innovation Solution
The proposed solution extends the range of chroma QP values to match the range of luma QP values, allowing for more aggressive quantization of chroma components. This is achieved by determining a QP index from the luma QP and a chroma QP offset, and then mapping this index to a chroma QP value, ensuring an upper limit of quantization step size for chroma matches that of luma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the maximum QP for chroma components is limited in existing video codec standards, then the decoding complexity is reduced and compatibility is maintained, but the bit allocation efficiency deteriorates and overall video quality is reduced
Solution Approach 1:
The patent extends the chroma QP range by modifying the parameter definition in the video codec standard. Specifically, it allows chroma QP to reach values up to 51 (matching luma QP range) by adjusting the clipping function parameters and QP derivation formulas, enabling more aggressive quantization of chroma components when needed for bit rate control
2Adaptability or versatility
If the chroma QP range is extended to match luma QP values, then the bit allocation flexibility is improved, but the decoder complexity increases
Solution Approach 1:
The patent extends the chroma QP range by modifying the parameter definition in the video codec standard. Specifically, it allows chroma QP to reach values up to 51 (matching luma QP range) by adjusting the clipping function parameters and QP derivation formulas, enabling more aggressive quantization of chroma components when needed for bit rate control
Solution Approach 2:
The decoder derives chroma QP values automatically from luma QP and chroma_qp_offset_cb/cr parameters using standardized formulas. This self-service mechanism allows the system to adapt chroma quantization dynamically without requiring complex external control logic, maintaining implementation simplicity while achieving flexible bit allocation
3Quantity of substance
If aggressive quantization of chroma components is applied, then the bitrate for chroma components is reduced, but the chroma quality deteriorates
Solution Approach 1:
The patent applies different quantization strengths to different color components locally. By independently controlling chroma QP through chroma_qp_offset_cb and chroma_qp_offset_cr parameters, the system can apply aggressive quantization (higher QP values) to chroma components while maintaining finer quantization (lower QP values) for luma components, achieving bit rate reduction with minimal perceptual impact
Data Source
AI summary
Innovations in control and use of chroma quantization parameter (“QP”) values that depend on luma QP values. More generally, the innovations relate to control and use of QP values for a secondary color component that depend on QP values for a primary color component. For example, during encoding, an encoder determines a QP index from a primary component QP and secondary component QP offset. The encoder maps the QP index to a secondary component QP, which has an extended range. The encoder outputs at least part of a bitstream including the encoded content. A corresponding decoder receives at least part of a bitstream including encoded content. During decoding, the decoder determines a QP index from a primary component QP and secondary component QP offset, then maps the QP index to a secondary component QP, which has an extended range.