Autofocus Lens Control via Scale Factor Accumulation
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Solution Overview
Problem
Existing autofocus systems in image-capture devices, such as webcams and security cameras, face challenges in quickly re-focusing during zoom-in or zoom-out movements, leading to increased time ranges for identifying the correct lens position, especially when scene changes occur due to camera or object movement.
Innovation Solution
The implementation of a feature-based evaluation using a scale factor to determine the correct lens direction and step dimension, allowing for rapid identification of the correct search direction and related steps, thereby reducing re-focusing time by utilizing the accumulated delta scale factor to detect zoom-in or zoom-out movements and adjust the lens position accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hill climbing search is used to re-focus after scene changes, then the system can identify the correct lens position, but the time range for re-focusing increases
Solution Approach 1:
The patent applies preliminary action by detecting zoom movements (zoom-in or zoom-out) before the actual refocusing is needed. By anticipating the direction of focus change based on zoom detection, the system pre-positions the lens in the correct direction, so when refocusing starts, the lens is already closer to the target position rather than having to search from the opposite end of the adjustment range.
Solution Approach 2:
The patent implements dynamics by making the lens search direction adaptive rather than fixed. The system dynamically adjusts the initial search direction based on detected zoom movements, allowing the refocusing process to move in the correct direction from the start rather than potentially searching in the wrong direction first. This dynamic adaptation significantly reduces the time range required to find the correct focus position.
2Speed
If the lens restarts search from the closest end of adjustment run, then the system can begin refocusing quickly, but the re-focusing time range increases when scene changes occur
Solution Approach 1:
The system performs preliminary detection of zoom movements to determine the correct initial search direction before the refocusing search begins. This preliminary action ensures that when the lens starts moving from the closest end of the adjustment run, it moves in the correct direction toward the new focus position rather than potentially searching in the wrong direction first.
Solution Approach 2:
The patent uses feedback by continuously monitoring zoom movement detection and using this information to adjust the initial lens search direction. The system feedback loop detects zoom-in or zoom-out movements and immediately uses this information to set the correct initial search direction for refocusing, creating a responsive system that adapts to scene changes in real-time.
Data Source
AI summary
In an embodiment, focusing an image-capture device such as, e.g., a camera including an optical system displaceable in opposite directions (A, B) via a focusing actuator, is controlled by evaluating a scale factor for the images acquired by the device. An accumulated value of the variations of the scale factor over a time interval (e.g., over a number of frames) is produced and the absolute value thereof is compared against a threshold. If the threshold is reached, which may be indicative of a zoom movement resulting in image de-focusing, a refocusing action is activated by displacing the optical system via the focusing actuator in the one or the other of the opposite focusing directions (A or B) as a function of whether the accumulated value exhibits an increase or a decrease (i.e., whether the accumulated value is positive or negative).