Region-Based Image Tone Correction for Natural HDR Gradation
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Solution Overview
Problem
Existing tone correction methods, such as high dynamic range synthesis (HDR), often result in over-correction or under-correction due to varying luminance distributions within an image, leading to unnatural images.
Innovation Solution
An image processing apparatus that divides an image into regions, determines correction characteristics for each region, and applies tone characteristics using a reference correction characteristic for one region, with others based on this reference, to maintain natural gradations and avoid saturation or blackout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tone correction is performed for each region in scenes with wide dynamic range, then tone characteristics are improved, but the image as a whole becomes unnatural
Solution Approach 1:
The patent applies different tone correction characteristics to different regions (subject region and background region) based on their luminance distributions. The subject region uses correction characteristics optimized for its luminance range, while the background region uses correction characteristics optimized for its luminance range, allowing each region to have appropriate tone characteristics without forcing uniform correction across the entire image, thus avoiding unnatural appearance
Solution Approach 2:
The patent dynamically adjusts correction characteristics by determining luminance distribution parameters (representative luminance values and luminance histograms) for each region and using these parameters to select or generate appropriate tone correction characteristics. This parameter-based approach allows the system to adapt correction strength and type to local luminance conditions, resolving the contradiction between precise tone correction and natural appearance
2Manufacturing precision
If correction characteristics are adjusted based on difference between representative luminance values, then tone correction is optimized, but over-correction or under-correction may occur
Solution Approach 1:
The patent incorporates feedback by determining luminance distribution parameters from the actual image data and using these feedback results to adjust correction characteristics. The representative luminance values and luminance histograms serve as feedback that guides the selection of appropriate correction characteristics, allowing the system to adapt to actual luminance conditions and avoid over-correction or under-correction
Solution Approach 2:
The patent makes correction characteristics dynamic by determining them based on the actual luminance distribution of each region rather than using fixed correction characteristics. The system dynamically adjusts correction parameters according to the measured luminance histograms and representative values, enabling adaptive correction that maintains consistency across different lighting conditions and avoids predictable over- or under-correction
Data Source
AI summary
An image processing apparatus, comprises at least one processor or circuit configured to function to: acquire an image; divide and classify the image into a plurality of regions based on predefined conditions; determine correction characteristics for correcting tone characteristics for each of the plurality of regions; and correct the tone characteristic of each of the regions using the correction characteristics corresponding to each of the regions. In the determination, the correction characteristics corresponding to one of the plurality of regions that is used as a reference is set as a reference correction characteristics, and for the correction characteristics other than the reference correction characteristics, the correction characteristics of at least a portion that has a luminance lower than a predetermined luminance are determined based on the reference correction characteristics.