Autofocus Control for Repetitive Patterns Using Defocus Feedback
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Solution Overview
Problem
Existing autofocus methods, particularly phase difference AF, face challenges in accurately focusing on subjects with periodic patterns, leading to incorrect focus detection and low reliability of defocus amounts.
Innovation Solution
A focus adjustment apparatus that includes an imaging unit, a focus detection unit, a control unit, a first determination unit for identifying repetitive patterns, and a second determination unit for assessing image blurring, which adjusts the focus lens based on the defocus amount when a repetitive pattern is detected and significant blurring is present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phase difference AF is used for subjects with periodic patterns, then focus detection can be performed, but incorrect focus points are detected due to false high correlation positions
Solution Approach 1:
The system performs focus detection multiple times at different focus lens positions and uses the change in defocus amount as feedback to determine the true in-focus position. By comparing the defocus amount change between different positions, the system can distinguish true focus from false correlation peaks caused by periodic patterns.
Solution Approach 2:
The system preliminarily determines whether the subject has a periodic pattern before performing focus detection. When a periodic pattern is detected, the system activates a special focus detection mode that moves the focus lens to a different position and recalculates the defocus amount, preventing false focus points from being selected.
2Ease of operation
If reliability evaluation of defocus amount is performed, then focus adjustment can be made, but reliability is insufficient for subjects with periodic patterns
Solution Approach 1:
The system evaluates reliability not only based on the initial defocus amount calculation but also on the change in defocus amount when the focus lens position is changed. This dual-stage feedback mechanism provides more reliable focus adjustment by verifying that the detected focus point remains consistent across different lens positions, even for periodic pattern subjects.
3Measurement precision
If correlation calculation is used to detect focus position, then focus detection is achieved, but false focal points are detected for periodic patterns
Solution Approach 1:
The system extracts and removes the influence of periodic patterns from the correlation calculation by performing focus detection at multiple focus lens positions. By comparing results across different positions, the system can identify and exclude false correlation peaks that arise from periodic patterns, keeping only the true focus information.
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 accurate focus adjustment operations even on subjects with periodic patterns by determining the degree of image blurring and adjusting the focus lens accordingly, improving the reliability and precision of autofocus detection.
Implementation Method 1
an imaging unit that converts light from an optical system to an electric signal by photoelectric conversion and outputs an image signal for imaging and a pair of parallax image signals
Data Source
AI summary
An imaging apparatus includes: a focus detection unit that detects a defocus amount using the pair of parallax image signals; a control unit that controls adjustment of a focus position based on the defocus amount; a first determination unit that determines whether a subject with a repetitive pattern is being imaged in a focus detection area; and a second determination unit that determines whether a degree of image blurring is equal to or more than a predetermined degree of blurring. When the first determination unit determines that a subject with a repetitive pattern is being imaged and the second determination unit determines that a degree of image blurring is equal to or more than the predetermined degree of blurring, the control unit moves a focus lens to acquire a new defocus amount.