Tone Curve Blending for HDR Image Shadow Reduction
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Solution Overview
Problem
Conventional tone mapping techniques, both global and local, suffer from image quality issues and shadow effects in images with significant brightness differences, limiting effective display of high dynamic range images.
Innovation Solution
An image processing method and apparatus that employs a combination of global, local, and histogram tone mapping, utilizing weighted sums and cumulative distribution functions to generate a final output tone curve, enhancing image visibility by adjusting luminance, resolution, and precision values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If global tone mapping is used, then processing simplicity is maintained, but image quality deteriorates on images with certain characteristics
Solution Approach 1:
The patent combines global tone mapping with histogram-based tone mapping by generating a final tone curve that integrates both approaches. The global tone mapping operator provides overall tone control while the histogram-based operator adjusts specific luminance distributions, merging their advantages to resolve the contradiction between processing simplicity and image quality.
Solution Approach 2:
The patent dynamically adjusts tone curve parameters based on histogram analysis of the input image. By changing the tone mapping parameters according to the actual luminance distribution characteristics, the system adapts to different image types, maintaining simplicity while improving quality for various image characteristics.
2Manufacturing precision
If local tone mapping is used, then image quality is improved, but shadow effects occur in regions with large brightness differences
Solution Approach 1:
The patent applies local quality adjustment through histogram-based tone mapping that operates on luminance distribution rather than individual pixels. This approach provides localized tone control in high-luminance regions while avoiding the shadow effects of conventional local tone mapping by using cumulative distribution functions to smoothly transition tones across brightness boundaries.
3Manufacturing precision
If histogram equalization is applied, then luminance distribution is improved, but outdoor visibility deteriorates
Solution Approach 1:
The patent modifies the histogram equalization parameter by introducing a weight value that controls the strength of histogram-based tone mapping. By adjusting this parameter, the system can reduce the aggressive luminance redistribution that harms outdoor visibility while maintaining the beneficial luminance distribution effects for general image quality.
Solution Approach 2:
The patent applies partial histogram equalization by combining it with global tone mapping rather than using full histogram equalization. This partial application maintains improved luminance distribution in critical regions while avoiding excessive luminance adjustments that would degrade outdoor visibility.
Data Source
AI summary
An image processing method includes transforming input image data into a histogram, equalizing the histogram using a cumulative distribution function, setting a first weight value based on the equalized histogram and a first reference value, generating a first tone curve based on the equalized histogram and the first weight value, generating a final output tone curve by applying a second weight value to the first tone curve and an output of a second tone curve applied to the input image data, and generating output image data based on the final output tone curve and the input image data.