Fisheye Image Histogram Masking for Accurate Exposure Adjustment
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Solution Overview
Problem
Existing image processing systems struggle to accurately display luminance histograms for images captured with all-around fisheye lenses, as underexposed areas cause peaks on the low-luminance side, making it difficult to set exposure correctly.
Innovation Solution
An image processing apparatus that determines the area where the optical image is formed on the image sensor and generates a histogram using luminance information only from this area, excluding underexposed regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a histogram is generated by acquiring luminance information from the whole imaging surface of the image sensor, then all pixel data is included in the histogram, but pixels positioned outside the optical image cause a high peak on the low-luminance side, making it impossible to easily confirm the distribution of luminance values within the optical image
Solution Approach 1:
The imaging surface is segmented into two distinct areas: the first area where the optical image is formed and the second area outside the optical image. The histogram generation process selectively uses luminance information only from the first area, excluding the second area. This segmentation resolves the contradiction by separating useful information (optical image pixels) from harmful information (underexposed pixels), enabling accurate luminance distribution measurement without the confounding low-luminance peak from outside-the-image pixels
Solution Approach 2:
Different areas of the imaging surface are treated differently in the histogram generation process. The first area (within optical image) contributes to the histogram while the second area (outside optical image) is excluded. This local quality approach ensures that the histogram reflects only the luminance distribution of the actual optical image, improving measurement precision and information visibility
2Reliability
If luminance information from the entire imaging surface is used for histogram generation, then complete pixel coverage is achieved, but underexposed pixels create a false high peak that obscures the true luminance distribution
Solution Approach 1:
The harmful component (luminance information from pixels outside the optical image) is extracted and removed from the histogram generation process. By taking out only the useful luminance information from pixels within the optical image area, the histogram accurately reflects the true luminance distribution, enabling reliable exposure setting without the obscuring effect of underexposed pixels
Solution Approach 2:
The patent converts the harmful effect of underexposed pixels into a benefit by using the design information to precisely define the optical image area. The exclusion of pixels outside this area, which would otherwise create false peaks, actually enhances the reliability of exposure setting by ensuring the histogram reflects only meaningful luminance data from the optical image
Data Source
AI summary
An image processing apparatus acquires image signals of an optical image which is formed by an image capturing optical system and captured by an image sensor, and design information of the image capturing optical system. Luminance information is detected from the image signals. A histogram of the luminance information is generated and displayed on a display device. A system controller determines, based on the design information, a first area in which the optical image is formed on an imaging surface of the image sensor, and generates the histogram by using luminance information of pixels included in the first area.