Autofocus Apparatus Offset Adjustment for High-Frequency Image Signal Asymmetry
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Solution Overview
Problem
The existing autofocus methods, such as contrast AF, face challenges in maintaining image quality due to aberrations and errors in lens manufacturing and assembly, especially when dealing with high spatial frequencies, leading to inaccurate focus detection and image blur.
Innovation Solution
An autofocus apparatus that adjusts the focus lens position based on an offset amount calculated from the shape of high-frequency components of the image signal, combining this with a predetermined amount determined by the optical system's characteristic information, to maintain image quality and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a higher frequency component is extracted to detect in-focus position, then the focus detection accuracy is improved, but the detecting reliability deteriorates due to noise and aberrations
Solution Approach 1:
The patent dynamically adjusts the frequency selection and offset amount based on detected asymmetry characteristics. The system transitions from a static approach (fixed frequency and offset) to a dynamic one where parameters are adapted in real-time according to the measured asymmetry, resolving the contradiction between accuracy and reliability
Solution Approach 2:
The patent changes parameters (frequency component selection and offset amount) based on the detected asymmetry characteristics. By adjusting these parameters dynamically, the system maintains focus detection accuracy while compensating for noise and aberration effects that would otherwise reduce reliability
2Speed
If a predetermined amount is used to move the focus lens, then the autofocus speed is improved, but the image quality deteriorates due to manufacturing errors and assembly errors
Solution Approach 1:
The patent introduces feedback by detecting asymmetry characteristics and using this information to adjust the offset amount. This closed-loop approach compensates for manufacturing and assembly errors, maintaining image quality while preserving the speed benefit of predetermined movement amounts
Solution Approach 2:
The patent performs preliminary detection of asymmetry characteristics to determine an appropriate offset amount before executing the focus adjustment. This preliminary action allows the system to compensate for potential errors in advance, ensuring image quality is maintained during the rapid autofocus operation
3Adaptability or versatility
If the focus lens is moved by a predetermined amount in defocus direction for the center, then the focus improving direction for the periphery is achieved, but the image quality drastically deteriorates on the steep slope side due to asymmetry
Solution Approach 1:
The patent explicitly addresses asymmetry by detecting asymmetry characteristics and adjusting the offset amount accordingly. Instead of treating the optical system as symmetric, the invention embraces the asymmetric nature of real optical systems and uses this information to compensate for quality deterioration on the steep slope side
Solution Approach 2:
The patent applies different offset amounts based on local asymmetry characteristics detected in different regions. By tailoring the compensation to the specific asymmetric conditions present, the system maintains image quality across the entire image area while preserving the adaptive focus adjustment capability
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
This approach effectively stabilizes the autofocus performance by minimizing the impact of aberrations and errors, preventing significant deterioration in image quality and focusing accuracy, even under conditions of high spatial frequencies and asymmetry.
Implementation Method 1
an image signal obtained by photoelectrically converting an object image formed by an image pickup optical system
Data Source
AI summary
An autofocus apparatus includes a control unit configured to set an offset amount based on information relating to a shape of a first high-frequency component of an image signal obtained by photoelectrically converting an object image formed by an image pickup optical system that includes a focus lens while driving the focus lens, and to move the focus lens to a position that shifts from a first position of the focus position by a sum of the offset amount and a predetermined amount that is determined by characteristic information of the image pickup optical system.