Rolling Shutter Camera Sub-Frame Illumination for Biometrics
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Solution Overview
Problem
Biometric identification systems using rolling shutter cameras face challenges in capturing high-quality images without causing user discomfort due to long exposure to high-intensity multi-spectral illumination, which can lead to eye blinking and reduced image quality.
Innovation Solution
Synchronizing a rolling shutter camera with a multi-spectral illumination source to switch on the illumination only during the sub-frame duration when capturing the eye region, using a short-duration high-intensity illumination followed by a lower intensity or turning off the light, thereby reducing exposure time and discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multi-spectral illumination source is kept on at high intensity during the entire image capture period, then sufficient lighting is provided for capturing the entire image, but user discomfort increases and eye blinking occurs due to prolonged exposure
Solution Approach 1:
The image capture process is divided into multiple segments corresponding to different regions (e.g., eyes, face). The illumination source is activated only during the capture of specific segments that require it, rather than continuously illuminating the entire scene. This segmentation allows high-intensity illumination to be applied selectively to reduce user discomfort while maintaining image quality for critical regions.
Solution Approach 2:
The illumination source operates in periodic pulses synchronized with the rolling shutter capture intervals. Instead of continuous illumination, the light is turned on and off in periodic cycles that match the camera's scan rate, providing illumination only when needed for each horizontal line or region capture, thereby reducing overall exposure time and user discomfort.
2Reliability
If multi-spectral illumination source is activated for the entire duration of image capture, then complete image illumination is achieved, but eye blinking increases reducing image quality
Solution Approach 1:
The system preliminarily identifies which regions of the image require high-intensity illumination (such as the eye region for biometric authentication) and pre-schedules the illumination activation times accordingly. This preliminary planning ensures that illumination is applied exactly when and where needed, preventing eye blinking in critical regions while avoiding unnecessary illumination that would cause discomfort.
Solution Approach 2:
Different regions of the image receive different illumination strategies. Critical regions such as the eyes receive high-intensity illumination only during their specific capture window, while other regions may receive reduced or no illumination. This local differentiation maintains image quality for authentication-critical areas without causing eye blinking from prolonged exposure.
3Loss of time
If rolling shutter camera captures image over extended time period, then sufficient time is available for image processing, but exposure to illumination increases causing user discomfort
Solution Approach 1:
The illumination source is synchronized with the rolling shutter's periodic scan pattern, activating in brief pulses that correspond to each horizontal line or region capture interval. This periodic illumination provides sufficient lighting for each captured segment while minimizing the total illumination duration, thereby reducing user discomfort during the extended capture process.
Solution Approach 2:
The extended capture time is divided into multiple sequential segments, each corresponding to a specific image region. Illumination is activated only during the segments that require it, allowing the camera to capture the entire image over an extended period for processing purposes while limiting user exposure to illumination only during necessary segments.
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 allows for high-quality image capture of the eye region without prolonged exposure to high-intensity light, reducing user discomfort and the chances of eye blinking, thereby improving the efficiency and accuracy of biometric authentication.
Implementation Method 1
The multi-spectral illumination source can include a light-emitting diode (LED) element
Data Source
AI summary
The technology described in this document can be embodied in a method for capturing an image. The method includes generating a first control signal configured to cause a rolling shutter camera to capture an image of a subject over a first time period. The method also includes generating, at a first time point during the first time period, a second control signal configured to set a multi-spectral illumination source at a first intensity level. The multi-spectral illumination source is configured to illuminate the subject. The method further includes generating, at a second time point during the first time period, a third control signal configured to set the multi-spectral illumination source at a second intensity level that is less than the first intensity level. A portion of the image captured by the rolling shutter camera between the first and second time points includes a target feature associated with the subject.