Tone Conversion Curve for Visually Equivalent Luminance
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Solution Overview
Problem
Conventional methods for adjusting contrast in HDR images fail to ensure that perceived changes in brightness for both dark and bright portions are equivalent, leading to undesirable image quality, especially when high luminance exceeds 1000 nits.
Innovation Solution
An image processing apparatus and method that perform tone conversion on RAW image data by generating a second tone conversion curve to adjust the luminance changes of bright and dark portions so that they are visually equivalent, using a visual differential threshold to ensure equivalent perceived changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional amplitude control method is used for contrast adjustment, then the contrast can be adjusted by controlling signal levels, but the perceived luminance change amounts for dark and bright portions are not equivalent
Solution Approach 1:
The patent applies parameter changes by modifying the tone conversion curve based on visual differential thresholds. Instead of using simple amplitude control with fixed reference levels, the system dynamically adjusts the tone conversion parameters to account for human visual perception characteristics, ensuring that luminance changes in both dark and bright portions are perceived as equivalent amounts.
2Illumination intensity
If HDR image data is displayed with high luminance exceeding 1000 nits, then the dynamic range is preserved, but the perceived luminance change equivalence between dark and bright portions deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the treatment of dark and bright portions in the tone conversion process. The system calculates visual differential thresholds separately for different luminance regions and applies region-specific adjustments to the tone conversion curve, ensuring that each region's luminance changes are perceived equivalently despite the wide overall dynamic range.
3Device complexity
If simple amplitude control is applied to maintain contrast, then the adjustment process is simple, but it cannot guarantee equivalent perceived adjustment amounts for dark and bright portions
Solution Approach 1:
The patent introduces visual differential thresholds as an intermediary parameter between the simple amplitude control and the final tone conversion. This intermediary allows the system to maintain a relatively simple adjustment process while incorporating human visual perception characteristics, thereby guaranteeing equivalent perceived adjustment amounts without significantly increasing system complexity.
Data Source
AI summary
An image processing apparatus operable to perform development processing by performing at least a tone conversion on RAW image data that is inputted image data, the image processing apparatus comprising: a setting unit configured to set a first tone conversion curve corresponding to a dynamic range of the image data; an adjusting unit configured to generate a second tone conversion curve by adjusting the first tone conversion curve so that luminance changes of a bright portion and a dark portion of the image data are visually equivalent; and a tone conversion unit configured to perform a tone conversion of the image data by using the second tone conversion curve.