Adaptive Phase Difference AF Threshold for Moving Subjects
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Solution Overview
Problem
The phase difference AF method in imaging devices faces limitations in detection accuracy, leading to errors in lens positioning and a higher probability of missing a shooting opportunity, especially when the phase difference amount exceeds the maximum detectable value.
Innovation Solution
An imaging device with a first and second signal detection unit in the pupil region of the imaging optical system, a focusing control unit that calculates defocus amounts and drives the focus lens, and a movement detection unit that adjusts the threshold value based on subject movement, allowing for enhanced accuracy and reduced missed opportunities by adjusting the number of focus calculations and lens movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the phase difference amount exceeds the maximum detectable value, then the defocus amount calculation becomes inaccurate, but performing multiple phase difference AF calculations to improve accuracy increases the time required for auto-focusing
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The focusing control unit dynamically adjusts the threshold for determining whether to perform multiple phase difference AF calculations based on the detected subject movement. When subject movement is detected, the threshold is set to a larger value, allowing single-calculation auto-focusing even for larger defocus amounts, thereby reducing auto-focusing time while maintaining acceptable accuracy for moving subjects.
2Speed
If the threshold value for determining single vs. multiple phase difference AF is increased, then auto-focusing speed improves for moving subjects, but measurement precision may be compromised for stationary subjects with large defocus amounts
Solution Approach 1:
The patent applies local quality by making the threshold value context-dependent rather than uniform. Different threshold values are applied based on the local condition of subject movement: a larger threshold is used when subject movement is detected (prioritizing speed), while a smaller threshold is used when no movement is detected (prioritizing precision). This allows the system to optimize for the appropriate characteristic based on the specific situation.
Solution Approach 2:
The patent changes the parameter of the threshold value based on the detected condition (subject movement). The focusing control unit modifies the threshold parameter dynamically: increasing it when movement is present to enable faster single-calculation auto-focusing, and decreasing it when no movement is present to ensure high-precision multi-calculation auto-focusing. This parameter adaptation resolves the contradiction between speed and precision.
3Measurement precision
If multiple phase difference AF calculations are performed to ensure accurate focusing, then measurement precision improves, but the probability of missing a shooting opportunity increases due to extended focusing time
Solution Approach 1:
The patent applies dynamics by making the number of phase difference AF calculations adaptive rather than fixed. The focusing control unit dynamically determines whether to perform single or multiple calculations based on subject movement detection and the calculated defocus amount. For moving subjects, even with larger defocus amounts, the system performs only single calculations to minimize focusing time and capture shooting opportunities, accepting reduced precision as a necessary trade-off for moving targets.
Data Source
AI summary
A digital camera includes a focusing-control-unit that calculates a defocus amount using detection signals of phase difference detection pixels and drives a focus lens according to the defocus amount, and a movement-detection-unit that detects whether a movement is present in a captured subject-image. The focusing-control-unit calculates the defocus amount according to an auto-focus instruction, and drives, in a case where the defocus amount exceeds a threshold-value, the focus lens according to the defocus amount and then performs the phase difference AF again to complete auto-focusing. Further, in a case where the defocus amount is equal to or smaller than the threshold-value, the focusing control unit performs the phase difference AF only once to complete the auto-focusing. Further, in a case where a movement is present in the subject-image, the focusing-control-unit sets the threshold to a larger value than in a case where a movement is not present in the subject-image.