Exposure Control Using Weighted NAM and Luminance Evaluation
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Solution Overview
Problem
Conventional exposure control methods in image capturing apparatuses are ineffective when white balance is significantly shifted, particularly when using image quality changing filters, as they fail to accurately adjust exposure due to tint influences and are not effective in chromatic color scenarios.
Innovation Solution
An image capturing apparatus and method that utilize a weighted average of NAM and luminance evaluation values for exposure control, adjusting weights based on the amount of image quality changing effect and the reliability of automatic correction processing, to improve exposure control performance by reducing the impact of tint changes and white balance shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the NAM evaluation value is used for exposure control, then exposure control performance is improved under normal white balance conditions, but exposure control accuracy deteriorates when white balance is significantly shifted due to image quality changing filters or chromatic colors
Solution Approach 1:
The patent changes the parameter used for exposure control from the NAM evaluation value (which is sensitive to white balance shifts) to the luminance evaluation value (which is insensitive to white balance shifts). This parameter change allows the system to maintain accurate exposure control under various white balance conditions, including when image quality changing filters or chromatic colors are present.
2Adaptability or versatility
If the luminance evaluation value is used for exposure control, then exposure control accuracy is maintained under white balance shifts, but exposure control performance deteriorates under normal conditions compared to using the NAM evaluation value
Solution Approach 1:
The patent dynamically selects between the NAM evaluation value and the luminance evaluation value based on the detected white balance shift amount. When the white balance shift is within a predetermined threshold, the NAM evaluation value is used for optimal performance under normal conditions. When the white balance shift exceeds the threshold, the luminance evaluation value is used to maintain accuracy under shifted conditions. This dynamic selection resolves the contradiction by adapting the evaluation method to the current operating conditions.
3Manufacturing precision
If image quality changing filters are applied, then image quality is improved, but exposure control accuracy deteriorates due to significant white balance shifts
Solution Approach 1:
The patent implements a feedback mechanism that detects the white balance shift amount caused by image quality changing filters and uses this information to select the appropriate evaluation value for exposure control. When a significant white balance shift is detected, the system switches to using the luminance evaluation value, which is insensitive to white balance shifts, thereby maintaining exposure control accuracy even when image quality changing filters are applied.
Data Source
AI summary
In an image capturing apparatus, a subject image is converted into an image signal, which undergoes automatic correction processing including white balance correction processing, and further undergoes image quality change processing. A first evaluation value indicating a largest value of an R signal, a G signal, and a B signal of the image signal undergone the image quality change processing and a second evaluation value indicating a luminance of the image signal undergone the image quality change processing are detected. A control evaluation value is calculated using weighted average of the first evaluation value and the second evaluation value according to at least one of an amount of image quality changing effect due to the image quality change processing and a reliability of the automatic correction processing, and exposure control is performed based on the control evaluation value.