Focus Detection Apparatus for Repetitive Pattern Objects
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Solution Overview
Problem
Phase difference detection methods in image-capturing apparatuses face accuracy issues when focusing on objects with periodic contrasts or repetitive patterns, as they struggle to differentiate between in-focus and out-of-focus states due to multiple local minimal correlation values.
Innovation Solution
A focus detection apparatus and method that acquire paired phase difference image signals through photoelectric conversion, calculate focus detection information based on phase differences, and determine feature values related to correlation values before and after focus lens drive, allowing for accurate focus detection even with repetitive patterns by selecting the most probable phase difference from candidate shift amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase difference detection method is used for focus detection, then focus detection speed is improved, but focus detection accuracy deteriorates when object has repetitive pattern
Solution Approach 1:
The system performs preliminary analysis of the correlation value waveform to detect multiple local minimal values before final focus determination. This preliminary detection of waveform characteristics allows the system to identify when it is dealing with a repetitive pattern object, enabling subsequent corrective actions to be taken in the focus calculation process.
Solution Approach 2:
The patent introduces an intermediary analysis step that examines the correlation value waveform between the initial phase difference measurement and the final focus determination. This intermediary waveform analysis acts as a mediator to detect the presence of multiple local minimal values and trigger appropriate handling procedures for repetitive pattern objects.
2Loss of information
If correlation calculation is performed on paired phase difference image signals, then focus state information is obtained, but multiple local minimal values cause focus detection failure for repetitive patterns
Solution Approach 1:
The system implements feedback by comparing the detected local minimal values with the lens drive direction and magnitude. After driving the focus lens based on an initial phase difference detection, the system feeds back by re-evaluating the correlation waveform and comparing the new local minimal values with previous ones to verify whether the correct focus state has been achieved, correcting errors if necessary.
Solution Approach 2:
The patent applies dynamics by making the focus detection process adaptive and iterative rather than static. The system dynamically adjusts its approach based on the detected waveform characteristics, performing multiple rounds of correlation calculation and lens driving with comparison of results across iterations to converge on the correct focus state.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and accurate focus detection and lens control, ensuring correct focus state determination even with objects having repetitive patterns, by analyzing correlation value waveforms and selecting the appropriate phase difference for focus lens drive.
Implementation Method 1
causes paired photoelectric converters to photoelectrically convert paired object images formed by dividing a pupil of the imaging optical system
Data Source
AI summary
The focus detection apparatus includes circuitry which function as a producer configured to acquire paired phase difference image signals that are produced through photoelectric conversion of an object image formed by an optical system including a focus lens and that have therebetween a phase difference corresponding to a focus state of the object image, and configured to produce focus detection information using the phase difference acquired from the paired phase difference image signals, and an acquirer configured to acquire a feature value relating to a correlation value between the paired phase difference image signals. The producer is configured to acquire the phase difference depending on a result of comparison between the feature values acquired before and after driving of the focus lens.