Backlight Compensation Using Luminance Boundaries
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Solution Overview
Problem
Existing methods for backlight compensation in digital images and videos obtained in backlight environments suffer from overexposure of the background, loss of chromatic information, and discontinuous luminance, leading to poor contrast and distinguishability of targets.
Innovation Solution
A method and apparatus that generate first and second luminance boundary values to perform nonlinear backlight compensation on pixel points within specific luminance ranges, using a quadratic compensation function to maintain luminance continuity and enhance image contrast without overexposing the background.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If exposure intensity is increased to brighten the target in backlight environment, then the luminance of the target is improved, but the background becomes overexposed with large white patches and loss of detail
Solution Approach 1:
The patent applies different compensation strategies to different regions of the image based on their luminance characteristics. Pixel points are classified into first type (lower luminance) and second type (higher luminance), and different compensation rates are applied accordingly. This local differentiation allows the target region to be brightened while preserving background detail, resolving the contradiction between improving target luminance and preventing background overexposure.
2Illumination intensity
If a compensation rate is used to compensate for the luminance of the entire image, then the luminance of the target is improved, but the contrast of the image is deteriorated
Solution Approach 1:
The patent calculates different compensation rates for different pixel points based on their individual luminance values and the luminance difference between foreground and background. This localized compensation approach maintains the relative luminance relationships within regions, preserving image contrast while still brightening the target. The compensation rate varies spatially rather than being uniform across the entire image.
3Illumination intensity
If linear compensation is applied to pixel points with luminance less than a fixed value, then the luminance of dim regions is improved, but chromatic information is lost and image layering occurs
Solution Approach 1:
The patent employs a dynamic, nonlinear compensation function rather than a fixed linear compensation rate. The compensation amount varies continuously based on the pixel's luminance value and its relationship to the luminance difference between foreground and background. This dynamic approach prevents the abrupt transitions and uniform scaling that cause image layering and chromatic information loss in linear compensation methods.
Data Source
AI summary
A method and an apparatus for processing images are disclosed. The method includes: generating an image histogram of an image to be processed; judging whether the image to be processed requires backlight compensation according to the image histogram; if the image to be processed requires backlight compensation, determining a first luminance boundary value A used for deciding whether to perform backlight compensation and a second luminance boundary value C used for deciding whether to perform positive or negative backlight compensation; and performing backlight compensation for the image to be processed according to the first luminance boundary value A and the second luminance boundary value C. The method is simple and universally applicable. After backlight compensation, the contrast of the image is high, and the image is free from background overexposure and image layering. The image photographed in a backlight environment is processed properly.