Autoexposure Control for Autofocus Latency in Low Light
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Solution Overview
Problem
Conventional autofocus systems in digital cameras suffer from increased latency and reduced accuracy in low light conditions due to increased exposure time, which decreases frame rate and introduces hand-shake blur, adversely affecting image sharpness statistics.
Innovation Solution
The system employs an autoexposure control mechanism to increase the frame rate and reduce exposure time, while also adjusting image signal gain to enhance image brightness, thereby assisting the autofocus operation and improving latency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exposure time is increased to reduce noise in low light conditions, then image quality is improved, but frame rate decreases and hand-shake blur increases
Solution Approach 1:
The system dynamically adjusts the frame rate based on lighting conditions and autofocus requirements. When in low light conditions, the system can increase the frame rate above the standard reciprocal of exposure time to maintain sufficient frames for autofocus processing, making the frame rate adaptive rather than fixed.
Solution Approach 2:
The system changes the frame rate parameter from its conventional fixed value (reciprocal of exposure time) to a variable value that can be increased when needed for autofocus operations in low light conditions, allowing the system to optimize between noise reduction and autofocus performance.
2Measurement precision
If exposure time is increased to reduce noise in low light conditions, then image quality is improved, but autofocus latency increases
Solution Approach 1:
The system dynamically increases the frame rate during autofocus operations in low light conditions, allowing more image data to be captured within the same time period, thereby reducing the time required for autofocus processing without compromising image quality through excessive exposure time.
Solution Approach 2:
The system performs preliminary actions by capturing additional image data at higher frame rates before final image capture, enabling the autofocus algorithm to process more data points and determine optimal focus more quickly, reducing overall autofocus latency.
3Measurement precision
If frame rate is decreased due to increased exposure time, then noise is reduced, but hand-shake blur increases
Solution Approach 1:
The system dynamically adjusts the frame rate to be higher than the standard reciprocal of exposure time when in low light conditions, capturing more image data that can be processed to compensate for hand-shake effects while maintaining the longer exposure time needed for noise reduction.
Solution Approach 2:
The system uses feedback from the increased frame rate data to detect and compensate for hand-shake motion, allowing the autofocus algorithm to select the sharpest frames and reduce the impact of hand-shake blur on the final image quality.
Data Source
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AI summary
In a particular embodiment, a method is disclosed that includes comparing a frame rate of image capture by an image sensor to a frame rate threshold at an image capture device. The method also includes when the frame rate is less than the frame rate threshold, increasing the frame rate to a modified frame rate that is greater than or at least equal to the frame rate threshold. The method further includes performing an autofocus operation on an image to be captured at the modified frame rate.