Dynamic Tone Mapping Curve for HDR Detail Preservation
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Solution Overview
Problem
Conventional High Dynamic Range (HDR) imaging technologies face challenges in accurately tone mapping HDR image data, often resulting in degraded images due to reliance on proper Auto Exposure (AE) settings and digital gain functions, leading to loss of detail and contrast, especially when lighting conditions are dynamic or not adequately matched by preconfigured AE modes.
Innovation Solution
A tone mapping function is generated to control the brightness of HDR image data, mapping tone values to match scene lighting conditions without relying on AE settings, using control points like low-tone, mid-tone, and high-tone points to define a parametric tone mapping curve that minimizes visual artifacts and compresses highlights, allowing transformation into Standard Dynamic Range (SDR) or Low Dynamic Range (LDR) image data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional digital gain function is applied to control HDR image brightness, then brightness control is achieved, but visual quality degrades with washed-out appearance and loss of detail
Solution Approach 1:
The patent applies a tone mapping function with multiple control points (black point, mid-tone point, white point) that selectively transforms different luminance ranges of the HDR image. This non-uniform parameter transformation preserves detail in shadow and highlight regions while achieving proper brightness control, avoiding the uniform scaling that causes washing out in conventional digital gain methods.
2Device complexity
If conventional tone mapping assumes proper AE settings, then tone mapping process is simplified, but image quality degrades when AE settings are improper
Solution Approach 1:
The tone mapping function automatically adapts to the actual HDR image characteristics by using the image's own luminance statistics (histogram analysis) to determine optimal control point positions. This self-adjusting mechanism eliminates dependency on pre-configured AE settings, making the system reliable across varying lighting conditions without adding complex manual configuration steps.
3Adaptability or versatility
If HDR image data is displayed on conventional SDR devices, then compatibility is improved, but dynamic range and visual quality are lost
Solution Approach 1:
The patent applies different mapping transformations to different luminance regions of the HDR image through the multi-point tone mapping function. Shadow regions, mid-tone regions, and highlight regions each receive optimized transformation parameters that preserve their local characteristics, maximizing the retention of visual detail and contrast when compressed to SDR format for conventional displays.
Data Source
AI summary
The various embodiments of the present disclosure are directed towards methods for tone mapping High-Dynamic-Range (HDR) image data, as well as controlling the brightness of the image encoded by HDR the image data and/or the tone-mapped image data. HDR image is captured. A tone mapping function for the HDR image data is generated. To generate the tone mapping function, control points are dynamically determined based on an analysis of the HDR image data. The tone mapping function is fit to the control points. The tone mapping function is a non-linear function, and is described by a curve in a plane. The shape of the curve is constrained by a line generated from a portion of the control points. The tone mapping function is applied to the HDR image data. A color-compression is applied to the tone mapped image data to generate Standard Dynamic Range or Low Dynamic Range image data.