HDR Luminance Adaptation Circuit for Color Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing technologies face challenges in displaying High Dynamic Range (HDR) images on displays with lower maximum luminance, as they struggle to accurately down-map brighter pixels without causing color errors or clipping.
Innovation Solution
The proposed solution involves an apparatus that calculates a tertiary image with a tertiary luminance dynamic range, using a receiver to process an image signal with metadata containing luma and saturation change functions. This apparatus includes a decoder with a luma mapper and chroma modifier, an inverse chromatic gamut mapper, and a display tuning circuit to adjust the image for any display maximum luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR images with high maximum luminance are displayed on displays with lower maximum luminance, then the display can show a wider range of luminance values, but color errors and clipping occur
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the saturation multiplier based on the display's maximum luminance capability. The system modifies the chroma components (Cb and Cr) by applying a saturation multiplier that is calculated as a function of the display's ML_D parameter, thereby adapting the color saturation to match the display's luminance capabilities and prevent color errors
Solution Approach 2:
The patent implements dynamics by making the saturation multiplier adjustable and display-specific rather than fixed. The saturation multiplier is calculated dynamically based on the ratio of the display's maximum luminance to the master HDR image's maximum luminance, allowing the system to adapt in real-time to different display capabilities and maintain color accuracy across varying luminance ranges
2Adaptability or versatility
If luminance down-mapping is applied to adapt HDR images to lower luminance displays, then the image can be displayed on various displays, but color saturation and accuracy are lost
Solution Approach 1:
The patent applies local quality by differentiating the processing of luma and chroma components. While the luma is down-mapped to match the display's luminance range, the chroma components are selectively adjusted using a saturation multiplier that preserves color information. This localized approach ensures that each color component is processed according to its specific requirements, maintaining color saturation while adapting to the display's capabilities
Solution Approach 2:
The patent implements preliminary action by calculating and applying the saturation multiplier before final color conversion to RGB. The system first determines the appropriate saturation multiplier based on the display's maximum luminance, then applies it to the chroma components, and finally converts to RGB. This preliminary adjustment of saturation ensures that color information is preserved throughout the down-mapping process
3Ease of manufacture
If a fixed luma mapping function is used for HDR to LDR conversion, then the conversion process is simple, but the output image does not match the master HDR image on displays with different maximum luminance
Solution Approach 1:
The patent implements dynamics by making the luma mapping function display-specific rather than fixed. The system generates a tailored luma mapping function for each display based on its maximum luminance capability (ML_D), ensuring that the mapping accurately reflects the display's characteristics. This dynamic approach maintains visual fidelity across different display types while keeping the conversion process computationally efficient
Data Source
Figure 1A~1D
Figure 2
Figure 3
AI summary
To obtain correct pixel colors, which correct chroma in addition to correct luminances for a display optimization in a system which involves change of chromaticity between a wide and narrow chromatic gamut, the inventor proposes an apparatus and method for calculating a tertiary image (Im_MDR) having a tertiary luminance dynamic range (DR_T), the apparatus comprising: a receiver for receiving an image signal (S_inp), which comprises an input image (Im_inp) of a first, lower luminance dynamic range (DR_L), in which pixel colors are coded by an input luma (Yin_LDR) and two input chroma color components (Cb_LDR_709, Cr_LDR_709), which input chroma color components are defined based on a first set of three primary colors (Pr_N, Pg_N, Pb_N), and which image signal comprises metadata (MET) which comprises a luma mapping function (F_L_L2H) for mapping various values of various pixels of the input luma to corresponding values of a secondary luma (Yin_HDR), wherein the secondary luma is a luma of a secondary image (Im_Sec) which has a second, higher luminance dynamic range (DR_H), and which metadata comprises a saturation change function (F_S_L2H) to change the two input chroma color components (Cb_LDR_709, Cr_LDR_709) into corresponding intermediate chroma color components (Cb_HDR_709, Cr_HDR_709) defined in a color system based on the same three primary colors (Pr_N, Pg_N, Pb_N); wherein the apparatus comprises a decoder (401) comprising a luma mapper (402) arranged to calculate the secondary luma (Yin_HDR) by applying the luma mapping function (F_L_L2H) to the input luma (Yin_LDR), and comprising a chroma modifier (403) arranged to determine the intermediate chroma color components (Cb_HDR_709, Cr_HDR_709) based on the input chroma color components (Cb_LDR_709, Cr_LDR_709) and the saturation change function (F_S_L2H); an inverse chromatic gamut mapper (410) arranged to map, keeping a range of lumas constant between input and output, the intermediate chroma color components (Cb_HDR_709, Cr_HDR_709) to secondary chroma color components (Cb_HDR_WG, Cr_HDR_WG) which have a higher saturation and are defined based on a second set of three primary colors (Pr_W, Pg_W, Pb_W) which have a higher saturation than the first set of three primary colors (Pr_N, Pg_N, Pb_N); characterized in that the apparatus comprises a display tuning circuit (430) which comprises: an input for a luma mapping function (i_FT) which is received from a tuned luma mapping function derivation circuit (420), which is arranged to receive the metadata which further comprises a mastering display white point luminance (MDWPL), and receive from a storage location (421) a value of a display maximum luminance (ML_D), and apply an algorithm which determines a display-tuned luma mapping function (FL-DT) which is a similarly shaped version of the luma mapping function (F_L_L2H) which lies closer to a 45 degree diagonal (diag); wherein the display tuning circuit (430) comprises a luma mapper (431) arranged to calculate a tertiary luma (Y_MDR) of the tertiary image, and comprises a saturation multiplier calculation circuit (432) arranged to calculate a saturation multiplier (gsat) and comprises a multiplier (435) arranged to multiply both secondary chroma color components (Cb_HDR_WG, Cr_HDR_WG) by the saturation multiplier to obtain tertiary chroma color components (Cb_MDR_WG, Cr_MDR_WG) of the tertiary image; wherein the saturation multiplier calculation circuit (432) comprises a luma determination circuit (433) to determine a corresponding value of the input luma (Yin_LDR) corresponding to a value of the secondary luma (Yin_HDR) of a pixel being processed, and to determine the saturation multiplier (gsat) as a function of a first factor (SF1) which depends on the corresponding value of the input luma (Yin_LDR) and a second factor (SF2) which depends on the luma mapping applied to the secondary luma (Yin_HDR)