Focus Detection Unit Dynamic Frequency Band Selection
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Solution Overview
Problem
In image capturing apparatuses, high gain conditions during low light environments lead to increased noise in high frequency components used for autofocus evaluation, reducing focusing accuracy and making focus adjustment more difficult.
Innovation Solution
The apparatus adjusts the frequency band used for autofocus evaluation based on the gain level, switching to lower frequency bands during high gain conditions to minimize noise influence, and combines low and high frequency components to generate a synthesis signal for accurate focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If gain is multiplied to compensate for darkness in low light environments, then brightness of the image is improved, but noise in the high frequency component increases
Solution Approach 1:
The patent changes the frequency band parameter dynamically based on gain magnitude. When gain is high (indicating low light conditions), the system switches from using high frequency components to using low frequency components for focus evaluation. This parameter adaptation resolves the contradiction by avoiding the noisy high frequency band when gain multiplication introduces significant noise.
2Measurement precision
If high frequency component is used for AF evaluation value, then focusing accuracy is improved under normal conditions, but focus adjustment becomes difficult under high gain conditions
Solution Approach 1:
The patent implements a dynamic switching mechanism that adapts the frequency band selection based on operating conditions (gain magnitude). Under normal conditions, high frequency components provide sharp focus evaluation. Under high gain conditions, the system dynamically switches to low frequency components, making focus adjustment feasible again. This dynamic adaptation resolves the contradiction between achieving high focusing accuracy and maintaining ease of operation across different lighting conditions.
Data Source
AI summary
An image capturing apparatus includes an image capturing unit configured to capture an image focused on a light receiving surface, a gain unit configured to multiply a gain to an image signal output from the image capturing unit and be able to electronically change brightness of an image that the image signal represents, and a focus signal generating unit configured to extract a signal in a frequency band from the image signal output from the gain unit and generate a focus signal from the extracted signal. The focus signal generating unit changes the frequency band for the signal to be used in generating the focus signal in accordance with the magnitude of the gain.