Image Capture Exposure Control Using Segmented Photometric Analysis
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Solution Overview
Problem
Existing exposure control methods in digital video cameras are unstable due to the fluctuation in the number of high luminance areas, leading to inconsistent exposure correction when controlling exposure based on photometric values.
Innovation Solution
An image capture apparatus and method that acquire both an average photometric value and a maximum photometric value from divided areas and high luminance areas, respectively, to calculate a third photometric value, which is used to correct exposure by adjusting the difference between this value and a reference value, ensuring stable exposure control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exposure control target value is determined based on the number of high luminance areas, then the exposure can be corrected for high luminance areas, but the exposure control target value becomes unstable due to fluctuation in the number of high luminance areas
Solution Approach 1:
The screen is divided into multiple areas, and photometric values are calculated separately for each area. The exposure control target value is determined by selecting the maximum photometric value among all areas, rather than using the overall average photometric value. This segmentation approach ensures that high luminance areas do not cause the entire screen's exposure target to become unstable.
Solution Approach 2:
The system continuously monitors photometric values from divided areas and dynamically adjusts the exposure control target value based on the maximum photometric value detected. This feedback mechanism ensures that the exposure control adapts to changing luminance conditions while maintaining stability through the selective use of maximum values rather than fluctuating averages.
2Manufacturing precision
If the exposure control target value is lowered to suppress high luminance areas, then excellent exposure can be obtained for objects in high luminance areas, but the overall exposure control becomes unstable
Solution Approach 1:
The exposure control is optimized for local high luminance areas by determining the exposure control target value based on the maximum photometric value among divided areas. This allows the system to provide excellent exposure quality for objects in high luminance areas without compromising the overall stability of the exposure control target value.
3Device complexity
If the average luminance value of the whole screen is used as the photometric value, then the exposure control is simple, but excellent exposure cannot be obtained for the main object when it exists in the central portion
Solution Approach 1:
The screen is divided into multiple areas with different weights assigned to each area when calculating the photometric value. The central portion is given a higher weight (e.g., doubled) compared to other portions. This segmented approach with weighted averaging maintains relative simplicity while significantly improving exposure quality for the main object located in the central portion.
Solution Approach 2:
Different weights are assigned to different areas of the screen based on the likelihood of the main object's location. The central portion receives higher weight, ensuring that exposure control prioritizes this area where the main object is most likely to be positioned, thereby improving exposure quality without excessive complexity.
Data Source
AI summary
An image capture apparatus comprises an image capturing unit that captures an object image and outputs image data; a photometric value acquisition unit that acquires, from the image data, a first photometric value and a second photometric value different from the first photometric value; and an exposure change unit that changes exposure such that the first photometric value comes close to a target value, wherein the exposure change unit calculates a third photometric value based on the first photometric value, the target value, and the second photometric value and corrects the exposure in accordance with a difference between the third photometric value and a reference value.