HDR Luma Mapping Adaptation for Display Peak Brightness
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Solution Overview
Problem
High dynamic range (HDR) video coding technologies face challenges in adapting image pixel luminances for displays with varying luminance dynamic ranges, leading to inconsistent rendering of bright and dark scenes, particularly when converting HDR images to Standard Dynamic Range (SDR) for legacy displays, resulting in unwatchable night scenes and loss of contrast.
Innovation Solution
An image pixel luminance adaptation apparatus that receives encoded HDR images and metadata specifying luma mapping functions, applies an algorithm to calculate display-adapted luma mapping functions based on the display's maximum luminance, combining original and alternative luma mapping functions to adjust pixel luminances for optimal rendering on displays with different peak brightness capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR images are converted to SDR for legacy displays, then compatibility with legacy displays is improved, but contrast and brightness fidelity are lost resulting in unwatchable night scenes
Solution Approach 1:
The patent implements dynamic tone mapping that adapts the conversion process based on the display's peak brightness capability. Instead of a static conversion, the system dynamically adjusts the tone mapping curve parameters according to the target display's characteristics, allowing optimal contrast preservation for each specific display device. This dynamic approach enables the system to maintain better contrast fidelity while ensuring compatibility across different display types.
Solution Approach 2:
The patent changes key parameters of the tone mapping function based on the display's peak brightness. By adjusting parameters such as the curve shape, knee point, and saturation levels according to the target display's capabilities, the system optimizes the conversion process. This parameter adaptation allows the system to preserve contrast and brightness fidelity better than fixed conversion methods, while still ensuring compatibility with legacy SDR displays.
2Measurement precision
If display-adapted luma mapping functions are calculated based on display maximum luminance, then rendering accuracy on specific displays is improved, but processing complexity increases
Solution Approach 1:
The patent performs preliminary calculations of display-adapted luma mapping functions by pre-determining the tone mapping parameters based on the display's peak brightness capability. This preliminary adaptation is done before the actual image rendering, allowing the system to store and reuse the adapted mapping functions for multiple images on the same display. This approach reduces per-image processing complexity while maintaining high rendering accuracy.
Solution Approach 2:
The patent introduces an intermediary display adaptation layer that sits between the HDR content and the display output. This intermediary component calculates and applies the display-specific luma mapping functions, acting as a mediator that translates HDR content to match the specific display's characteristics. By isolating the complex adaptation logic in this intermediary layer, the system achieves high rendering accuracy without overwhelming the overall processing complexity.
3Adaptability or versatility
If multiple luma mapping functions are combined for different display brightness levels, then adaptability to various displays is improved, but computational overhead increases
Solution Approach 1:
The patent applies partial adaptation by selectively combining luma mapping functions based on the specific display's peak brightness level. Instead of applying all possible mapping functions to all images, the system selects and combines only the relevant functions needed for the current display configuration. This partial approach maintains adaptability across different display types while significantly reducing the computational overhead compared to applying all mappings universally.
Solution Approach 2:
The patent segments the luma mapping function combination process by dividing it into distinct ranges based on display peak brightness levels. Different combination strategies are applied to different brightness segments (e.g., low brightness displays vs. high brightness displays). This segmentation allows the system to optimize the computational approach for each segment, improving adaptability while managing computational overhead through targeted rather than universal processing.
Data Source
AI summary
To enable a better and more adjustable manner of HDR video display adaptation, applicants inventor contributed an image pixel luminance adaptation apparatus (500), comprising: a connection (501) to a comprised or connectable video decoder (207), which video decoder is arranged to receive an encoded high dynamic range image (Im_COD), which is encoded according to a first maximum codeable luminance (PB H), and which video decoder is arranged to receive metadata specifying at least one luma mapping function (F_ct; FL_50t1_1), which at least one luma mapping function specifies the offsets of luminances of a secondary image corresponding to the encoded high dynamic range image compared to the luminances of the same pixel positions as encoded in the encoded high dynamic range image, which secondary image has a second maximum codeable luminance (PB_S) which preferably is at least 4× smaller or larger than the first maximum codeable luminance (PB_H), and the video decoder being arranged to output a decoded high dynamic range image (Im_RHDR) and the luma mapping function; a display adaptation unit (401) arranged to receive a value of a display maximum luminance (PB_D) that a particular display can display as brightest pixel color, and an input luma mapping function, and the display adaptation unit being arranged to apply an algorithm which calculates at least one display adapted luma mapping function based on the input luma mapping function and the display maximum luminance (PD_D), wherein this at least one display adapted luma mapping function corresponds in shape to the input luma mapping function but lies closer to a 45 degree increasing diagonal of a graph of the input luma mapping function in perceptually uniformized axes, depending on the difference between the value of the display maximum luminance (PB_D) and the first maximum codeable luminance (PB_H) relative to the difference between the second maximum codeable luminance (PB_S) and the first maximum codeable luminance (PB_H); characterized in that the image pixel luminance adaptation apparatus comprises an alternative luma mapping function determination unit (502) arranged to determine an alternative luma mapping function (ALT_FL_50t1_1) and wherein the display adaptation unit (401) comprises a combination unit (503) which is arranged to combine the at least one luma mapping function (F_ct; FL_50t1_1) and the alternative luma mapping function (ALT_FL_50t1_1) into a combined luma mapping function (CMB_FL_50t1_1), and wherein the display adaptation unit is arranged to apply its algorithm on as input luma mapping function the combined luma mapping function; the image pixel luminance adaptation apparatus comprising a luma mapping unit (510) arranged to receive pixel lumas of the decoded high dynamic range image (Im_RHDR) and to apply to those pixel lumas the combined luma mapping function to obtain output lumas of an output image (Im_DA); the image pixel luminance adaptation apparatus comprising an output image or video communication cable or wireless channel, to which a display can be connected, and an output signal formatter (230) arranged to send the output image (Im_DA).