Phase Difference Focus Detection Error Correction
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Solution Overview
Problem
Existing phase-difference focus detection methods in image capture apparatuses face errors due to misalignment, optical aberrations, and electrical crosstalk, leading to incorrect focus detection even when the image forming and focus detecting pixels are in-focus, especially when the F-number of the imaging optical system changes.
Innovation Solution
An image capture apparatus with a two-dimensional CMOS sensor where image forming and focus detecting pixels are arranged on the same plane, using microlenses and divided photoelectric conversion portions to correct image shift errors through a focus detection unit and controller, which calculates lens movement based on detected image shift and corrects for errors using pre-determined correction values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase difference detection is performed using image forming pixels and focus detecting pixels arranged on the same plane, then focus detection speed is improved, but image shift error occurs due to luminous flux scattering and electrical crosstalk
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for image shift error in a lookup table before actual focus detection. During focus detection, the appropriate correction value is retrieved and applied to compensate for scattering and crosstalk effects, enabling high-speed detection while maintaining precision without real-time complex calculations.
Solution Approach 2:
The patent implements feedback by using the correlation between focus detection signals to detect image shift error and then applying correction based on this detected error. The correction value is determined through correlation processing and used to adjust the focus detection results, creating a closed-loop system that maintains precision despite pixel arrangement limitations.
2Measurement precision
If correction for spatial misalignment is applied, then focus detection error from misalignment is reduced, but correction amount cannot change when F-number changes
Solution Approach 1:
The patent applies dynamics by making the correction value variable rather than fixed. The correction value is dynamically determined based on the F-number of the imaging optical system and the position in the imaging area. This allows the correction to adapt automatically to different shooting conditions, resolving the contradiction between precision and adaptability.
Solution Approach 2:
The patent implements parameter changes by varying the correction value according to changing system parameters (F-number and imaging area position). The correction is not a static value but changes as system conditions change, enabling the system to maintain focus detection precision across different F-numbers while adapting to the specific optical characteristics of each shooting condition.
3Measurement precision
If correction for optical aberration is applied, then focus detection error from aberration is reduced, but deviation between best imaging focal position and calculated focal position remains
Solution Approach 1:
The patent applies local quality by determining correction values specific to each imaging area position rather than using a uniform correction. The correction is tailored to the local optical characteristics at different positions in the imaging area, accounting for position-dependent aberrations and scattering effects. This enables precise focus detection while accurately determining the best imaging focal position for each location.
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 enables high-precision correction of focus detection errors, maintaining accurate focus detection across varying F-numbers and reducing the impact of optical aberrations and electrical crosstalk, ensuring precise focus adjustment.
Implementation Method 1
each of the pixels having one microlens and a photoelectric conversion portion that has been divided into a plurality of portions
Implementation Method 2
a plurality of pixels that photoelectrically convert an object image formed by an imaging optical system
Data Source
AI summary
An image capture apparatus includes: an image sensor having a plurality of pixels that photoelectrically convert an object image formed by an imaging optical system, each of the pixels having one microlens and a photoelectric conversion portion that has been divided into a plurality of portions; a focus detection unit configured to correct an image shift amount detected with a phase difference detection method using focus detection signal arrays of two images obtained by the photoelectric conversion portions divided into a plurality of portions; and a controller that calculates information corresponding to a movement amount of a lens of the imaging optical system based on the image shift amount detected and corrected by the focus detection unit, and controls movement of the lens of the imaging optical system.