HDR Image Saturation Processing via Luminance Mapping
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Solution Overview
Problem
Current HDR image processing technologies face challenges in optimizing pixel colors, particularly saturation, to achieve a correct artistic look on displays with varying peak brightness, as they struggle to adapt HDR content created for a specific peak brightness to displays with different dynamic ranges, leading to suboptimal rendering and loss of image quality.
Innovation Solution
A method and apparatus for processing color saturation in HDR images, involving a luminance mapping function and initial saturation processing, which calculates a display-tuned luminance mapping function and applies a final saturation processing function based on a secondary luminance value, ensuring accurate luminance and saturation adjustment for different dynamic range scenarios, allowing for optimal image rendering across various display peak brightness levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If HDR image content is created for a specific peak brightness (e.g., 5000 nit reference display), then the image achieves optimal luminance distribution and artistic look on that specific display type, but the image rendering quality deteriorates on displays with different peak brightness capabilities
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting saturation multipliers based on the ratio between the reference display peak brightness and the actual display peak brightness. The saturation processing function uses different multiplier values for different luminance ranges, allowing the image to adapt to various display capabilities while maintaining optimal color appearance. This resolves the contradiction by making the rendering process adaptable to different display parameters rather than being fixed for a single reference display.
Solution Approach 2:
The patent implements dynamics by introducing a dynamic saturation adjustment mechanism that changes processing parameters based on the actual display's peak brightness capability. The system calculates appropriate saturation multipliers in real-time based on the display characteristics, transforming a static rendering process into a dynamic one that adapts to different viewing conditions and display hardware.
2Manufacturing precision
If saturation is increased to enhance color vibrancy in HDR images, then the artistic look and visual appeal improve, but color accuracy and natural appearance deteriorate
Solution Approach 1:
The patent applies local quality by implementing different saturation multipliers for different luminance ranges within the image. Instead of applying a uniform saturation boost across all pixels, the system uses higher saturation multipliers for certain luminance ranges and lower multipliers for others, allowing selective enhancement of color vibrancy in appropriate regions while maintaining color accuracy in other regions. This resolves the contradiction by making saturation enhancement spatially and luminance-wise selective rather than global.
3Manufacturing precision
If multiple re-grading functions are created for different display peak brightness levels, then image quality on each specific display type improves, but system complexity and processing overhead increase
Solution Approach 1:
The patent applies universality by creating a single saturation processing function that can handle multiple display peak brightness levels through dynamic parameter adjustment. Rather than requiring separate re-grading functions for each display type, the universal processing function adapts to different displays by calculating appropriate saturation multipliers based on the display's peak brightness capability. This resolves the contradiction by making one processing function serve multiple purposes across different display scenarios.
Data Source
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AI summary
To enable better color and in particular color saturation control for HDR image handling systems which need to do luminance dynamic range conversion, e.g. from a SDR image to an image optimized for rendering on a display of higher display peak brightness and dynamic range, the inventors invented an apparatus (400) for processing a color saturation (C'bL, C'rL) of an input color (Y'L, C'bL, C'rL) of an input image (Im RLDR) to yield an output color (Y'M, Cb'M, Cr'M) of an output image (Im3000nit) corresponding to the input image, which output image is a re-grading of the input image characterized by the fact that its pixel colors have a different normalized luminance position (Y2) compared to the normalized luminance positions of the input colors (Yl), the normalized luminances being defined as the luminance of a pixel divided by the respective maximal codeable luminance of the image's luminance representation, whereby the ratio of the maximum codeable luminance of the input image and the maximum codeable luminance of the output image is at least 4 or larger, or 1/4thor smaller, the apparatus comprising a luminance processor (401) arranged to apply a display tuned luminance mapping function (F_L_da) to determine an output luminance (Y'M) from the input luminance (Y'L) of the input color, the apparatus further comprising a saturation factor determination unit (402) arranged to calculate a final saturation processing strategy (b; Bcorr) based on an initial saturation processing strategy (F _sat) and based on a secondary luminance value (Y'_H) which is derivable from the output luminance (Y'M) by applying a luminance mapping function (F M2H) which is based on the luminance mapping function (F_L_s2h).