Dynamic Softclipping Transfer Function for Video Contrast
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for improving contrast in images on displays, such as LCDs, face limitations in applying high gains due to hardclipping issues, which result in loss of local details and reduced contrast, especially in scenes with many dark samples or when using dynamic backlighting.
Innovation Solution
A method involving a transfer function with a slope greater than one in the gain region and a slope between zero and one in the softclip region, allowing for high gain application without hardclipping, by using a combination of linear gain and softclip functions defined across the entire displayable range, ensuring all output levels remain within the displayable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a gain is applied to increase video levels and improve contrast, then perceived contrast increases, but video levels may exceed the displayable range causing hardclipping and loss of local details
Solution Approach 1:
The patent divides the transfer function into two segments: a first segment with slope >=1 for dark regions that provides contrast enhancement, and a second segment with slope >=1 for light regions that prevents hardclipping. This segmentation allows different gain behaviors in different luminance regions, enabling high gain application without causing hardclipping in the overall image.
Solution Approach 2:
The patent applies different transfer function characteristics to different regions of the image based on their luminance values. Dark regions receive higher gain (slope >=1) to improve perceived contrast, while light regions use a transfer function that ensures output levels remain within the displayable range. This local differentiation resolves the contradiction by allowing aggressive contrast enhancement only where it benefits image quality without causing hardclipping.
2Illumination intensity
If a high gain is applied to compensate for reduced backlight luminance in DBL, then brightness perception is maintained, but contrast improvement is limited due to hardclipping constraints
Solution Approach 1:
The transfer function is segmented into a first segment for dark samples with slope >=1 that provides contrast improvement, and a second segment for light samples that prevents hardclipping. This allows the system to apply high gain (up to 4x or more) to compensate for DBL backlight reduction while maintaining both brightness perception and contrast improvement without the limitations of conventional unity-gain approaches.
3Illumination intensity
If a transfer function with slope >=1 is used to improve contrast in dark regions, then perceived contrast increases, but output levels may exceed the maximum displayable value requiring hardclipping
Solution Approach 1:
The transfer function is divided into a first segment with slope >=1 that operates on dark samples to improve perceived contrast, and a second segment with slope >=1 that operates on light samples to ensure output levels remain within the displayable range. The adaptive pivot point determines where the transition between segments occurs, ensuring that dark regions receive contrast enhancement while light regions are protected from hardclipping.
Data Source
AI summary
A method for improvement of contrast in an image shown on a display having a range of displayable video levels. The method comprises providing input video levels representing the image, said levels being within said displayable range; providing a transfer function (120, 121) having a slope greater than one everywhere in a gain region (130) of said displayable range, and a slope greater than zero and less than one everywhere in a softclip region (131) of said displayable range, said regions (130, 131) meeting at a threshold level (125), the transfer function (120, 121) being adapted to transfer any input video level within said displayable range to an output level within displayable said range; and transforming said input levels into output levels within said range, using the transfer function (120, 121). According to the invention, instead of “hardclipping” there is a “softclipping” of levels. Hence, compared to conventional methods, a higher gain may be used. In practical situations, the gain applied in the gain region typically may be up to 4.