Phase Difference Prediction for Accurate Focus Lens Control
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Solution Overview
Problem
The phase difference AF method in imaging devices faces challenges in accurately determining the phase difference, especially in low contrast or low brightness conditions, leading to incorrect focus lens positioning and potential overshooting or undershooting.
Innovation Solution
A focusing control device with multiple signal detection units and a phase difference prediction unit that calculates and predicts phase differences based on correlation calculations and historical prediction errors, allowing for precise focus lens control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase difference calculation is performed using correlation calculation of signal groups from different pupil areas, then focusing speed is improved, but measurement precision of phase difference deteriorates in low contrast or low brightness conditions
Solution Approach 1:
The patent introduces a feedback mechanism where the calculated phase difference is used to predict the next focus lens position, and this predicted position feeds back into the correlation calculation process. The system continuously refines the phase difference calculation by comparing predicted positions with actual correlation results, thereby improving measurement precision while maintaining fast focusing speed through the phase difference AF method.
Solution Approach 2:
The patent performs preliminary correlation calculations at multiple candidate phase difference values before final determination. By pre-calculating correlation values for several possible phase differences and selecting the most accurate one based on correlation strength, the system ensures high measurement precision even in challenging lighting conditions while maintaining overall focusing speed.
2Speed
If focus lens is driven based on calculated phase difference, then focusing response speed is improved, but reliability of focus positioning deteriorates due to overshooting or undershooting
Solution Approach 1:
The patent implements dynamic focus lens driving where the drive amount is continuously adjusted based on real-time correlation calculation results. Instead of fixed-step driving, the system modifies the drive amount dynamically according to the correlation strength and phase difference changes, preventing overshooting while maintaining rapid focusing response. The drive amount is optimized at each step based on current imaging conditions.
Solution Approach 2:
The system uses feedback from correlation calculation results to adjust focus lens driving parameters. The phase difference calculation and correlation strength information feed back into the drive control mechanism, allowing the system to correct positioning errors and prevent both overshooting and undershooting, thereby improving reliability while maintaining fast response.
3Measurement precision
If multiple signal detection units are used for correlation calculation, then measurement precision of phase difference is improved, but device complexity increases
Solution Approach 1:
The patent segments the pupil area into multiple regions, with each region having dedicated signal detection units. This segmentation allows parallel correlation calculations across different pupil areas, improving phase difference measurement precision through multiple independent measurements. The segmented approach distributes the complexity across modular detection units rather than requiring a single complex detector.
Solution Approach 2:
The patent designs signal detection units with multi-functionality, where the same detection units serve both phase difference calculation and focus lens drive control functions. This universal design reduces overall device complexity by eliminating redundant components while maintaining high measurement precision through the multi-unit correlation calculation approach.
Data Source
AI summary
Disclosed are a focusing control device which performs focusing control by a phase difference AF method with high accuracy, a lens device, an imaging device, a focusing control method, and a non-transitory computer readable recording medium storing a program. A digital camera includes a phase difference calculation unit which calculates the phase difference between a signal group output from a plurality of pixels 52A and a signal group output from a plurality of pixels 52B, a lens drive control unit which drives a focus lens according to a drive amount corresponding to the phase difference, a phase difference prediction unit which, based on a coefficient for converting a phase difference calculated at an arbitrary time to a drive amount and the difference between a movement amount of the focus lens and the drive amount, calculates a predicted value of the phase difference.