Autofocus Oscillation Prevention via Phase Contrast Switching
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Solution Overview
Problem
Existing autofocus mechanisms in electronic devices with cameras, such as phase detection autofocus, often experience oscillation issues when focusing on scenes with high frequency details or strong lines, leading to inaccurate focusing due to the finite size of focus sensors and the separation of light views.
Innovation Solution
A method that transitions from phase detection autofocus to contrast detection autofocus when an oscillation condition is detected, by obtaining and comparing lens position phase differences to determine if a switch is necessary, thereby avoiding oscillation and ensuring accurate focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase detection autofocus is used, then focusing speed is improved, but focusing accuracy deteriorates when scene features have high frequency details or strong lines
Solution Approach 1:
The system continuously monitors lens position phase differences and compares successive measurements to detect oscillation conditions. When oscillation is detected, the system switches from phase detection to contrast detection autofocus, using feedback from the oscillation detection mechanism to adjust the focusing method and eliminate the harmful oscillation behavior.
Solution Approach 2:
The patent changes the operational parameter by switching between two different autofocus mechanisms (phase detection and contrast detection) based on detected conditions. When high frequency scene features cause phase detection to oscillate, the system transitions to contrast detection which uses different measurement principles, thereby adapting the parameter set to avoid the oscillation problem while maintaining focusing capability.
2Adaptability or versatility
If phase detection autofocus is used, then autofocus capability is improved, but system stability deteriorates due to oscillation on high frequency scenes
Solution Approach 1:
The patent implements a dynamic switching mechanism that adapts the autofocus system's operational mode based on real-time conditions. The system transitions from phase detection to contrast detection autofocus when oscillation is detected, creating a dynamically adjustable system that maintains stability across varying scene characteristics while preserving the speed advantages of phase detection when conditions are favorable.
3Measurement precision
If focus sensors are made smaller to improve resolution, then measurement precision is improved, but the ability to capture sufficient light deteriorates
Solution Approach 1:
The patent makes the autofocus system multi-functional by implementing both phase detection and contrast detection capabilities. This allows the system to use phase detection (which can utilize larger sensor areas for better light capture) when scene conditions permit, and switch to contrast detection (which can achieve precise focusing without relying on large sensor areas) when phase detection becomes unstable, thereby achieving universality across different scene types.
Data Source
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AI summary
A method and device for auto-focus control in an imaging device is provided. The imaging device includes a lens. In one aspect, a method includes: obtaining a first lens position phase difference; after obtaining the first lens position phase difference, detecting lens movement; obtaining a second lens position phase difference; comparing the second lens position phase difference to the first lens position phase difference to determine whether the second lens position phase difference is greater than the first lens position phase difference; and in response to determining that the second lens position phase difference is greater than the first lens position phase difference, determining autofocus settings by a contrast detection method.