Tone Curve Mapping for HDR Image Conversion
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Solution Overview
Problem
Existing methods for displaying high dynamic range (HDR) images are limited as they require creating multiple versions of content in different formats, and existing tone curve determination techniques face challenges in achieving a one-to-one mapping, controlling contrast, and handling mid-tone anchor points effectively.
Innovation Solution
A tone curve mapping method using up to four segments, including optional linear and spline segments, controlled by three anchor points and three slopes, which allows for precise mapping of HDR images from one dynamic range to another, ensuring monotonicity and explicit control over contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple versions of content are created in different formats for HDR and SDR displays, then compatibility with various display devices is improved, but content creation complexity and processing time increase
Solution Approach 1:
The patent applies universality by creating a single HDR content version that can be adaptively converted to multiple display formats (HDR and SDR) through automatic tone curve mapping. The system determines optimal tone curves based on target display characteristics, allowing one content version to serve multiple display types without requiring separate creation processes for each format.
2Ease of manufacture
If existing tone curve techniques are used for HDR to SDR mapping, then implementation simplicity is maintained, but mapping precision and contrast control deteriorate
Solution Approach 1:
The patent applies parameter changes by introducing a parameterized tone curve model with multiple controllable parameters (anchor points, slopes, curvature). This allows precise control over the mapping characteristics while maintaining automated determination of parameter values based on input and target display characteristics. The system balances precision through multiple parameters with simplicity through automatic parameter selection.
Solution Approach 2:
The patent applies dynamics by making the tone curve parameters adaptive rather than fixed. The system dynamically determines optimal anchor points, slopes, and curvature based on the specific input image characteristics and target display properties. This dynamic adaptation enables precise mapping for different content and display combinations while maintaining automated operation.
3Manufacturing precision
If complex tone curve parameters are used to control contrast and anchor points, then mapping precision is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-determining optimal parameter values through automated analysis of input image statistics and target display characteristics. The system calculates appropriate anchor points, slopes, and curvature parameters before executing the actual tone mapping. This preliminary determination of parameters simplifies the computational process during real-time or near-real-time conversion while maintaining high mapping precision.
Data Source
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AI summary
Methods for mapping an image from a first dynamic range to a second dynamic range are presented. The mapping is based on a function that includes two spline polynomials determined using three anchor points and three slopes. The first anchor point is determined using the black point levels of the input and target output, the second anchor point is determined using the white point levels of the input and target output, and the third anchor point is determined using mid-tones information data for the input and target output. The mid-tones level of the target output is computed adaptively based on an ideal one-to-one mapping and by preserving input contrast in both the blacks and the highlights. An example tone-mapping transfer function based on third order (cubic) Hermite splines is presented.