White Balance Gain Correction for Night View Images
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Solution Overview
Problem
Existing image-capturing apparatuses face challenges in maintaining accurate white balance, particularly in images with a high proportion of dark areas, as the nonlinear output characteristic of dark regions can lead to color reproduction issues when gains are adjusted based on bright areas.
Innovation Solution
An image-capturing apparatus with a white balance gain calculator and a gain correction unit that determines and adjusts white balance gains based on the luminance and color differences of pixels, using a correction coefficient when the ratio of dark pixels exceeds a threshold, to prevent shifts in white balance, especially in night view images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If white balance gain is calculated based on bright area information, then white balance adjustment is simplified and processing efficiency is improved, but color reproduction accuracy deteriorates in images with high proportion of dark areas
Solution Approach 1:
The patent applies local quality by differentiating processing approaches for bright and dark areas. It calculates white balance gain primarily from bright area pixels (where color information is reliable) but applies correction coefficients to compensate for dark area characteristics. This allows the system to use bright area information for efficient gain calculation while addressing the specific nonlinear characteristics of dark areas through targeted correction, thus resolving the contradiction between processing efficiency and color accuracy.
Solution Approach 2:
The patent changes parameters by introducing correction coefficients that modify the white balance gain based on image characteristics. When the proportion of dark pixels exceeds a threshold, the system adjusts the gain calculation by applying correction coefficients derived from dark area pixel statistics. This parameter adjustment allows the system to maintain efficient bright-area-based processing while compensating for dark area color reproduction issues.
2Loss of information
If white balance adjustment uses information from the entire image including dark areas, then comprehensive color information is utilized, but white balance accuracy deteriorates due to nonlinear output characteristics in dark regions
Solution Approach 1:
The patent extracts only the reliable color information from bright area pixels for white balance gain calculation, excluding dark area pixels that contain unreliable color data due to nonlinear sensor characteristics. By separating the image into bright and dark areas and using only bright area information for primary gain calculation, the system prevents contamination from inaccurate dark area data while still processing the entire image for final output.
Solution Approach 2:
The patent introduces correction coefficients as an intermediary mechanism. These coefficients are calculated based on dark area pixel statistics and are used to adjust the white balance gain to compensate for dark area color reproduction issues. This intermediary allows the system to use bright area information for accurate gain calculation while still addressing the color reproduction problems in dark areas without directly using unreliable dark area color data.
3Measurement precision
If correction processing is applied to dark areas, then color reproduction accuracy in dark regions is improved, but device complexity increases
Solution Approach 1:
The patent applies partial action by implementing correction processing only when necessary - specifically when the proportion of dark pixels in the image exceeds a predetermined threshold. The system first calculates white balance gain from bright areas, then evaluates the dark pixel proportion, and only applies correction coefficients if the threshold is exceeded. This conditional approach provides dark area color improvement only when needed, avoiding unnecessary processing complexity in images where correction is not required.
Data Source
AI summary
There is provided a technique of preventing occurrence of a shift in white balance even when the ratio of a dark area is greater than the ratio of a bright area as in the case of a night view. A white balance gain calculator calculates white balance gains for an image from color of pixels whose luminance levels are at equal to or greater than a reference luminance level among all pixels of an image. When the ratio of dark pixels whose luminance satisfies a predetermined condition, among all pixels of the image, is equal to or greater than a reference ratio, a correction coefficient calculating section determines a correction coefficient from at least one of factors; namely, image-capturing sensitivity corresponding to an image, the ratio of dark pixels, and firing/non-firing of flash light; and instructs the white balance gain calculator to make a correction to the white balance gain in accordance with the correction coefficient.