Low-light Autofocus Using Extended Exposure Frames
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Solution Overview
Problem
Passive autofocus techniques, such as phase-detection and contrast-detection autofocus, are less effective in low-light conditions due to insufficient contrast or bright objects, leading to challenges in accurately focusing cameras in such environments.
Innovation Solution
The method involves extending the exposure time for autofocus frames based on the tolerated motion blur, allowing for enhanced autofocus performance without additional optics or sensors, by determining an extended exposure time and capturing frames that improve light gathering and autofocus accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive autofocus procedures are used in low-light conditions, then cost is reduced (no additional rangefinder equipment), but autofocus accuracy deteriorates due to insufficient contrast or bright objects
Solution Approach 1:
The patent changes the exposure time parameter from its traditional short duration to an extended duration specifically for low-light autofocus conditions. This parameter change allows the image sensor to accumulate more photons during the autofocus measurement, thereby improving the signal-to-noise ratio and enabling accurate contrast detection even in low-light environments without adding any hardware components.
Solution Approach 2:
The patent implements dynamic adjustment of exposure time based on detected light conditions. The system automatically extends the exposure time when low-light conditions are detected during autofocus operation, and uses normal exposure times under adequate lighting conditions. This dynamic adaptation allows the same passive autofocus system to maintain accuracy across varying light conditions.
2Measurement precision
If exposure time is extended for low-light autofocus, then autofocus accuracy is improved, but motion blur increases
Solution Approach 1:
The patent applies partial action by using motion blur selectively and acceptably only for the autofocus measurement purpose, while keeping the final image capture free of motion blur. The extended exposure time that would normally create unacceptable motion blur in a final image is tolerated during autofocus because the autofocus algorithm can still extract valid contrast information from the blurred frame, and no final image is produced from this extended exposure.
Solution Approach 2:
The patent segments the imaging process into distinct phases: an extended exposure phase for autofocus measurement only, and a separate normal exposure phase for final image capture. This segmentation allows the system to use aggressive extended exposure times during autofocus without compromising the quality of the final deliverable image, as the two functions are separated in time and purpose.
3Shape
If traditional autofocus exposure time is used, then motion blur is minimized, but autofocus accuracy deteriorates in low-light conditions
Solution Approach 1:
The patent implements dynamic adjustment of exposure time based on detected light conditions. The system automatically extends the exposure time when low-light conditions are detected during autofocus operation, and uses normal exposure times under adequate lighting conditions. This dynamic adaptation allows the same passive autofocus system to maintain accuracy across varying light conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances autofocus accuracy in low-light conditions by increasing the confidence level of the in-focus lens setting, allowing for better image capture in environments with limited light, such as night or dimly lit rooms.
Implementation Method 1
Other cameras (e.g., digital cameras) electrically capture image data (e.g., using a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensors)
Data Source
AI summary
The present disclosure relates to a low-light autofocus technique. One example embodiment includes a method. The method includes receiving an indication of a low-light condition for a camera system. The method also includes determining an extended exposure time for a low-light autofocus procedure of the camera system. Further, the method includes capturing, by the camera system, an extended frame for the low-light autofocus procedure. The extended frame is captured by the camera system using the determined extended exposure time. In addition, the method includes determining, based on the captured extended frame, an in-focus lens setting for a lens of the camera system.