Chroma QP Offset Calculation for HDR Video Color Quality
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Solution Overview
Problem
Existing methods for determining quantization parameter (QP) values for chroma components in video encoding and decoding lead to visual color artifacts, especially in High Dynamic Range (HDR) video, due to inconsistent QP settings between chroma and luma components.
Innovation Solution
An efficient method for calculating QP values for chroma components is introduced, which involves determining a QP offset based on the difference between the capture and encoded color spaces, allowing for adaptive adjustment of chroma QP values relative to the luma QP values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same QP value is used for both luma and chroma components, then the encoding complexity is reduced, but visual color artifacts appear especially in HDR video
Solution Approach 1:
The patent applies different QP values to different color components (luma and chroma) based on their specific characteristics. The chroma QP is adjusted separately from the luma QP using a offset mechanism, allowing each component to be optimized independently according to its importance and the HDR/WCG characteristics, thereby reducing visual artifacts while maintaining manageable complexity.
Solution Approach 2:
The patent introduces a chroma_qp_offset_cb and chroma_qp_offset_cr parameter that modifies the base chroma QP value based on the difference between capture and encoded color spaces. This parameter change allows adaptive adjustment of chroma quantization to prevent visual artifacts in HDR video while maintaining encoding efficiency.
2Object-affected harmful factors
If the QP value for chroma is reduced to improve color quality, then chroma blocking artifacts are reduced, but the bitrate increases
Solution Approach 1:
The patent dynamically adjusts the chroma QP offset based on the difference between capture and encoded color spaces. By calculating the appropriate offset value, the system reduces chroma blocking artifacts only when necessary (when color space conversion causes visible degradation), thereby improving color quality without unnecessarily increasing bitrate for all cases.
Solution Approach 2:
The patent applies QP adjustment selectively rather than uniformly. The chroma_qp_offset is applied only when the color space difference indicates potential artifact problems, allowing partial correction of chroma quality issues without fully reducing QP across all scenarios, thus balancing artifact reduction with bitrate efficiency.
3Quantity of substance
If the QP value for chroma is increased to reduce bitrate, then the bitrate decreases, but visual color artifacts become more prominent
Solution Approach 1:
The patent calculates an optimal chroma_qp_offset value that balances bitrate efficiency with artifact prevention. The offset is derived from color space characteristics, allowing the system to maintain higher QP (lower bitrate) when color space conversion is minimal, while automatically reducing QP (increasing bitrate) when artifacts are likely, thus achieving adaptive bitrate-quality optimization.
4Object-affected harmful factors
If adaptive QP adjustment for chroma is implemented, then color quality is improved, but the encoding complexity increases
Solution Approach 1:
The patent introduces a relatively simple parameter (chroma_qp_offset_cb/cr) that can be calculated from color space characteristics. This single offset parameter simplifies the adaptive QP adjustment process compared to more complex approaches, allowing color quality improvement through a manageable increase in encoding complexity that focuses on key parameters rather than comprehensive re-optimization.
Data Source
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AI summary
A QP offset value is calculated for a chroma component of a pixel in a picture of a video sequence based on a reference QP value and a factor that depends on a difference between a capture color space for the pixel and an encoded color space for the pixel. A QP value is then calculated for the chroma component based on the reference QP value reduced by the QP offset value. The calculation of QP values for chroma components based on the factor that depends on the difference between capture and encoded color spaces improves the chroma quality in an efficient way in particular for HDR and WCG video.