Colour Conversion Mapping Circuitry for HDR to SDR Hue Preservation
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Solution Overview
Problem
There is a need to convert digital images or video signals from one color space to another, such as from Rec 2020 to Rec 709, without undesirable changes in hue, brightness, and saturation, as certain colors in one space may not be representable in another, leading to disappointing image quality when displaying HDR images on SDR displays or vice versa.
Innovation Solution
A color conversion apparatus and method that maps pixels from an input color space to an intermediate color space where hue is consistent and independent of brightness and saturation, and then converts these pixels to an output color space, using techniques like matrix operations, gamma functions, and scaling to maintain hue while adjusting brightness and saturation, thereby ensuring that all pixels fall within the representable range of the output color space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct color space conversion is performed from input color space to output color space, then conversion speed is improved, but color accuracy deteriorates because hues change undesirably when colors are mapped outside the representable range
Solution Approach 1:
The patent introduces an intermediate color space with a gamut that encompasses both the input and output color spaces. Colors are first converted to this intermediate space where all colors can be represented, then mapped to the output color space. This intermediary step prevents direct mapping errors that would cause hue changes, thereby maintaining color accuracy while enabling conversion between different color spaces.
2Adaptability or versatility
If color clipping is applied to map colors outside the output color space gamut, then device compatibility is improved, but image quality deteriorates due to noticeable hue changes and color distortion
Solution Approach 1:
By using an intermediate color space as a mediator, the patent allows colors from the input color space to be represented accurately before conversion to the output color space. This approach maintains device compatibility by enabling conversion to various output color spaces while preserving image quality through the intermediate representation that prevents clipping-induced distortion.
Solution Approach 2:
The patent effectively adds a dimensional layer by introducing an intermediate color space between the input and output color spaces. This additional dimension provides a larger gamut that can accommodate all input colors, allowing for lossless conversion and preventing the quality degradation that would occur with direct clipping-based conversion methods.
3Measurement precision
If gamma correction and color matrix operations are applied, then color space conversion accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent utilizes parameter changes in the intermediate color space representation to facilitate accurate color conversion. By transforming colors into an intermediate space with different parametric characteristics (IPT color space with perceptually uniform parameters), the conversion process achieves higher accuracy through systematic parameter transformations rather than complex iterative calculations.
Data Source
AI summary
Colour conversion apparatus comprises mapping circuitry configured to map pixels of an input image having colour components in an input colour space to pixels of an mapped image having colour components in an output colour space, the input colour space and the output colour space being different colour spaces such that at least a subset of colours representable in the input colour space are not representable in the output colour space; the mapping circuitry being configured to: convert pixels from the input colour space to an intermediate colour space in which a colour space representation of hue approximates to a consistent perceived hue independent of brightness and/or saturation; map pixels in the intermediate colour space which lie outside a region of the intermediate colour space corresponding to representable colours in the output colour space to generate mapped pixels so that the mapped pixels lie within that region, by varying the brightness and/or saturation of those pixels in the intermediate colour space but leaving the hue of those pixels substantially unchanged; and convert the mapped pixels from the intermediate colour space to the output colour space.