Camera Autofocus Using Variable Step Lens Movement
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Solution Overview
Problem
Current automatic focus methods in cameras face challenges in balancing focusing speed and precision, often resulting in slow focus speeds and potential trapping at local poles due to fixed step lengths in focus motor movement.
Innovation Solution
A method and device for camera rapid automatic focusing that calculates estimated and determined focus values at multiple positions using different frequency bands, determines the direction and speed of lens movement based on rate of change and preset thresholds, allowing for adaptive movement until reaching the focus position corresponding to the maximum estimated focus value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed small step length is employed when searching for focus motor travel, then focusing precision can be maintained, but focusing time increases and focus speed decreases
Solution Approach 1:
The patent applies dynamics by making the step length variable rather than fixed. The step length changes based on the current focus state and rate of change of focus values, allowing the system to take larger steps when far from focus and smaller steps when approaching the optimal focus position, thus resolving the contradiction between speed and precision
Solution Approach 2:
The patent changes the parameter of step length dynamically during the focusing process. By adjusting the step length based on the rate of change of focus values and current focus position, the system optimizes both focusing speed and precision, avoiding the trade-off inherent in fixed step length approaches
2Productivity
If the step length is increased to reduce sampling points, then automatic focusing speed increases, but focusing precision decreases due to sparse sampling near peak value
Solution Approach 1:
The patent makes the step length dynamic, increasing it when the focus motor is far from the optimal position to speed up the process, and decreasing it when approaching the peak to ensure precise sampling and accurate focus detection, thus resolving the speed-precision trade-off
3Device complexity
If a fixed step length is used in focus motor movement, then the control algorithm is simple, but the system gets trapped at local poles and focus speed decreases
Solution Approach 1:
The patent implements feedback by continuously monitoring the rate of change of focus values and using this information to adjust the step length dynamically. This feedback mechanism helps the system escape local poles by detecting when the focus value stops increasing and reversing direction, while maintaining relatively simple control logic
Solution Approach 2:
The patent changes the step length parameter based on the focus search progress and detected local poles. By adapting the step length to the current search state, the system improves focus speed without significantly increasing algorithmic complexity
Data Source
AI summary
The disclosure discloses a method and device for camera rapid automatic focusing. The method comprises: driving a lens to move to multiple different focus positions to acquire image data of a object, and calculating a corresponding estimated focus value in a first high frequency and a corresponding determined focus value in a second high frequency for each image data; calculating a rate of change between a current determined focus value and a previous determined focus value, and determining a direction of movement of the lens on the basis of the rate of change being either positive or negative; comparing the rate of change with a preset focus change threshold, and determining a speed of movement of the lens on the basis of a comparison result; and repeating said steps until the lens moves to a focus position corresponding to a maximum of the estimated focus values.