Autofocus Search Interval Calculation for Single-Step Focus Detection
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Solution Overview
Problem
Existing autofocus systems in electronic cameras require a long time to detect focus position as they need to search for it twice, once over a wide search interval and again over a narrow interval, to ensure accuracy.
Innovation Solution
A focusing apparatus and method that calculates a proper search interval based on contrast characteristics and focal length, allowing for single AF search with highly accurate focus detection by using an image pickup device, search interval calculating device, focus evaluation value acquiring device, and focus detecting device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-step search process (wide search interval followed by narrow search interval) is used to detect focus position, then focus detection accuracy is improved, but the time required for focus detection increases significantly
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the search interval based on contrast characteristics and focal length. Instead of using fixed wide or narrow search intervals, the system calculates an optimal search interval that varies with imaging conditions, enabling accurate focus detection within a single search process.
Solution Approach 2:
The patent performs preliminary calculation of contrast characteristics and determination of optimal search interval before executing the focus search. This preliminary action allows the system to prepare the appropriate search parameters in advance, eliminating the need for sequential wide-to-narrow search processes.
2Loss of time
If a single AF search with a fixed search interval is performed, then the time required for focus detection is reduced, but focus detection accuracy deteriorates
Solution Approach 1:
The patent introduces dynamics by making the search interval variable rather than fixed. The search interval is dynamically adjusted based on real-time analysis of contrast characteristics and current focal length, allowing the system to adapt to different imaging conditions while maintaining both speed and accuracy.
Solution Approach 2:
The patent implements feedback by continuously monitoring contrast characteristics during the search process and using this information to verify and adjust the search interval. This feedback mechanism ensures that the single search process achieves accurate focus detection by validating results against measured contrast data.
3Reliability
If the search interval is set broadly to cover all possible focus positions, then the risk of missing the focus peak is reduced, but the number of evaluation points increases and processing time extends
Solution Approach 1:
The patent applies local quality by concentrating search effort on the most promising focus regions rather than uniformly evaluating all possible positions. By using contrast characteristics to identify areas with potential focus peaks, the system directs evaluation resources to locally optimal regions, improving both reliability and speed.
Solution Approach 2:
The patent uses partial action by performing focus search only in regions where contrast characteristics indicate potential focus positions, rather than exhaustively searching the entire range. This selective approach maintains reliability by focusing on high-probability areas while improving productivity by reducing unnecessary evaluations.
Data Source
AI summary
A focusing apparatus according to an aspect of the present invention comprises: an image pickup device which obtains an image signal of a subject that is captured by an image capturing device, wherein the image capturing device incorporates a focus optical system therein; a search interval calculating device which acquires contrast characteristics that are obtained for a subject of a predetermined spatial frequency at a predetermined focal length and calculates a search interval in capturing of an image based on the contrast characteristics; a focus evaluation value acquiring device which moves a focus lens to a detecting point for each search interval in a predetermined searching range and acquires a focus evaluation value at each detecting point from the image signal; and a focus detecting device which detects a focus position by using the focus evaluation value at each detecting point that is acquired by the focus evaluation value acquiring device.