Perceptual Code Space Transcoding for HDR Display Rendering
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Solution Overview
Problem
Modern displays struggle to accurately render high dynamic range (HDR) images due to their limited dynamic range capabilities, leading to visually noticeable errors and artifacts when compared to the original scene-referred HDR images.
Innovation Solution
The implementation of a perceptual nonlinearity-based image data exchange method using a contrast sensitivity function (CSF) model to generate a reference gray scale display function (GSDF), which optimally maps digital code values to gray levels, allowing for efficient transcoding of HDR image data across different display capabilities, minimizing errors and preserving perceptual details.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If HDR image data is delivered to end users' display devices for rendering, then the dynamic range rendering capability is improved, but device-specific and manufacturer-specific image transformations cause large amounts of visually noticeable errors
Solution Approach 1:
The patent transforms image data from scene-referred HDR parameter space to display-referred parameter space using perceptual mapping functions. This parameter transformation approach allows HDR content to be accurately rendered on displays with varying dynamic range capabilities by adjusting the mapping parameters based on the target display's characteristics, thereby resolving the contradiction between improved dynamic range rendering and maintained image rendering accuracy.
Solution Approach 2:
The patent introduces a perceptual mapping function as an intermediary between the HDR image data and the display device. This intermediary performs device-specific transformations that account for the display's dynamic range limitations while preserving perceptual accuracy, thus mediating between the high dynamic range content and the constrained display capabilities to minimize visually noticeable errors.
2Quantity of substance
If scene-referred HDR images are converted into post-production formats for transmission and storage, then the data transmission and storage efficiency is improved, but the dynamic range is significantly reduced leading to loss of perceptual details
Solution Approach 1:
The patent applies perceptual quantization that changes the parameter representation of HDR image data. Instead of uniformly quantizing the entire dynamic range, the system uses non-linear quantization steps that are denser in perceptually critical regions and coarser in less critical regions. This parameter transformation maintains perceptual details while enabling efficient compression and storage, resolving the contradiction between data efficiency and information preservation.
3Device complexity
If conventional displays with standard dynamic range are used, then the device complexity is reduced, but the rendering accuracy of HDR content deteriorates with visible banding and contour distortion
Solution Approach 1:
The patent enables conventional displays to self-adjust their rendering characteristics by incorporating display characterization and adaptive tone mapping. The system measures or queries the display's actual luminance response and automatically adjusts the image data transformation parameters to match the display's capabilities. This self-service approach allows standard displays to render HDR content with minimized banding and contour distortion without requiring complex hardware modifications.
Data Source
AI summary
A handheld imaging device has a data receiver that is configured to receive reference encoded image data. The data includes reference code values, which are encoded by an external coding system. The reference code values represent reference gray levels, which are being selected using a reference grayscale display function that is based on perceptual non-linearity of human vision adapted at different light levels to spatial frequencies. The imaging device also has a data converter that is configured to access a code mapping between the reference code values and device-specific code values of the imaging device. The device-specific code values are configured to produce gray levels that are specific to the imaging device. Based on the code mapping, the data converter is configured to transcode the reference encoded image data into device-specific image data, which is encoded with the device-specific code values. A display can natively process the device-specific image data to accurately reproduce a corresponding front of panel perceptual light, according to a perceptual curve electro-optical transfer function.