Variable ISO Exposure Control for Backlit Subject Underexposure
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Solution Overview
Problem
Conventional image pickup apparatuses face challenges in preventing underexposure of subjects, especially when ISO sensitivity is set to 'ISO Auto' and a subject is photographed against a brighter object like a street lamp at night, leading to inappropriate exposure.
Innovation Solution
An image pickup apparatus with variable ISO sensitivity setting and an exposure controller that adjusts weighting factors between different photometry areas within the photographing frame, switching between divisional average metering and center-weighted metering modes based on ISO sensitivity to ensure optimal exposure, particularly by prioritizing the central area when the subject is against the light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ISO sensitivity is set to 'ISO Auto' to enable automatic exposure adjustment, then the camera can adapt to dark lighting conditions, but the exposure control is interfered by brighter objects (such as street lamps) causing the subject to become underexposed
Solution Approach 1:
The photographing frame is divided into multiple photometry areas (first photometry area and second photometry area) with different weighting factors. The exposure controller selectively weights these areas based on ISO sensitivity settings, preventing bright objects from dominating the overall exposure calculation and causing subject underexposure.
Solution Approach 2:
Different photometry areas are assigned different weighting factors based on their importance for exposure control. The first photometry area (typically central or subject-containing area) is given higher weight when ISO sensitivity is high, while the second photometry area receives lower weight, creating local quality differences in exposure control.
2Device complexity
If the weighting factors of photometry areas are fixed, then the exposure control is simple, but the exposure cannot be optimized for different ISO sensitivity settings and lighting conditions
Solution Approach 1:
The weighting factors of the photometry areas are made variable rather than fixed. The exposure controller dynamically adjusts the weighting factors based on the ISO sensitivity setting, switching between different photo-metering modes (divisional average metering and center-weighted metering) to optimize exposure for different lighting conditions.
Data Source
AI summary
An image pickup apparatus includes an automatic exposure controller automatically controls ISO sensitivity in response to the output signal of an exposure metering circuit, and controls the exposure so that exposure setting is determined based on the brightness values of both the central photometry area and the remaining photometry area of an imaging frame. The automatic exposure controller controls the exposure setting so that when the ISO sensitivity is set to its higher value, the weighting factor of the central photometry area is higher than that of the remaining photometry area. The automatic exposure controller further determines whether or not a light source is behind an object, and, if it is the case, reduces the adjusted exposure setting so as to increase the amount of light incident on the image pickup apparatus.