HDR to SDR Tone Mapping via Anchor Point Transfer Functions
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Solution Overview
Problem
Current display systems, including consumer TVs, are unable to reproduce high dynamic range (HDR) images, necessitating the creation of multiple content formats, which is inefficient and confusing for consumers. Existing methods for down-converting HDR to standard dynamic range (SDR) often fail to preserve contrast and brightness accurately.
Innovation Solution
A method for mapping HDR images to SDR using a processor that determines a transfer function with three anchor points, based on black, mid-tones, and white points in both dynamic ranges, employing piece-wise linear or sigmoid functions to ensure accurate brightness and contrast preservation across different display ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR content is created in multiple formats (HDR and SDR versions), then compatibility with both HDR and SDR displays is improved, but content creation complexity and storage requirements increase
Solution Approach 1:
The patent implements a universal HDR content format that can be displayed on both HDR and SDR displays through automatic tone mapping. The system uses a transfer function with adjustable anchor points that adapts the content rendering based on the display capabilities, eliminating the need for separate HDR and SDR versions while maintaining compatibility with both display types.
Solution Approach 2:
The patent changes the rendering parameters dynamically based on display characteristics. By adjusting the anchor points of the transfer function according to the target display's luminance range and color volume, the same HDR content can be optimally rendered on different display types without requiring multiple versions of the content.
2Adaptability or versatility
If existing tone mapping methods are used to down-convert HDR to SDR, then display compatibility is improved, but contrast and brightness preservation deteriorates
Solution Approach 1:
The patent performs preliminary color grading and tone mapping adjustments during the HDR content creation phase. By pre-configuring the transfer function with appropriate anchor points that preserve the intended contrast and brightness relationships, the content maintains its visual quality when down-converted to SDR displays without requiring lossy post-processing.
Solution Approach 2:
The patent incorporates feedback mechanisms that monitor the luminance distribution and contrast characteristics of the HDR content. This feedback is used to automatically adjust the transfer function parameters to preserve the original image's contrast and brightness relationships during the tone mapping process, ensuring high-quality rendering on SDR displays.
3Speed
If a simple linear transfer function is used for HDR to SDR mapping, then processing speed is improved, but image quality and contrast preservation deteriorates
Solution Approach 1:
The patent segments the luminance range into multiple regions defined by anchor points, applying different mapping strategies to different segments. This piece-wise approach allows the system to preserve contrast and brightness in critical regions while maintaining processing efficiency, achieving a balance between image quality and processing speed that simple linear mapping cannot provide.
Data Source
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AI summary
Methods for mapping an image from one dynamic range to another dynamic range are presented. The mapping is based on a sigmoid-like function determined by three anchor points. The first anchor point is determined using the black point levels of a reference and a target display, the second anchor point is determined using the white point levels of the reference and target displays, and the third anchor point is determined using mid-tones information data for the input image and the mid-tones level of the target display. The mid-tones level of the target display is computed adaptively based on a desired range of constant brightness and a mapping function. The mapping function mapping may be piece-wise linear (in the log domain), piece-wise continuous, or a sigmoid. Examples for mapping high dynamic range images to standard dynamic range displays are presented.