Image Capture Apparatus Focus Detection Correction
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Solution Overview
Problem
Conventional automatic focus detection methods in image capture apparatuses fail to accurately correct focus detection errors caused by optical system aberrations, as they do not consider the focus condition of the captured image and represent only single frequency spatial characteristics, which is insufficient for evaluating the frequency bandwidth required in focus detection.
Innovation Solution
An image capture apparatus and method that utilize weighted addition of image-forming position information from an image sensor to correct focus detection results, using first and second evaluated bands for spatial frequencies, allowing for accurate focus detection by comparing and correcting the focus detection results based on the position of the focusing lens within the imaging optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a correction value suitable for the AF evaluation frequency unique to a camera body is used to correct the focus detection result, then the focus detection result can be corrected according to camera-specific characteristics, but the focus detection error cannot be sufficiently corrected because the focus condition of the captured image is not considered
Solution Approach 1:
The patent segments the focus detection correction process into multiple components: (1) camera body-specific correction values based on AF evaluation frequency, and (2) captured image-specific correction values based on focus condition. By dividing the correction into these segments, the system can apply appropriate corrections for each aspect without losing important information, thereby resolving the contradiction between using camera-specific correction and maintaining focus condition information.
Solution Approach 2:
The patent changes the parameters used in focus detection correction from a single camera-specific parameter to multiple parameters including focus condition parameters derived from the captured image. By introducing additional parameters (focus condition information) while retaining the original camera-specific parameters, the system achieves more accurate correction without losing essential information.
2Device complexity
If the AF evaluation frequency represents only spatial frequency characteristics of a single frequency, then the measurement process is simplified, but the frequency bandwidth required for actual focus detection evaluation is not adequately represented
Solution Approach 1:
The patent transitions from evaluating a single frequency dimension to evaluating a frequency bandwidth dimension. Instead of using a single AF evaluation frequency, the system evaluates a range of frequencies (frequency bandwidth) that better represents the actual focus detection requirements. This dimensional expansion from point-frequency to band-frequency resolves the contradiction between simplicity and comprehensive representation.
Data Source
AI summary
An image capture apparatus can execute automatic focus detection of an imaging optical system, using a signal obtained from an image sensor. First image-forming position information is obtained by performing, using first weights, weighted addition on information regarding image-forming positions of the imaging optical system, the information corresponding to different spatial frequencies. In addition, second image-forming position information is obtained by performing, using second weights, weighted addition on the information. A result of the automatic focus detection is corrected based on a result of a comparison between the first and second image-forming position information. The first weights correspond to an evaluated band at the time of appreciating an image, and the second weights correspond to an evaluated band of the signal used in the automatic focus detection.