Fingerprint Image Sensing Dynamic Exposure Control
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Solution Overview
Problem
Fingerprint identification systems face issues with image overexposure due to varying finger widths, pressing angles, and environmental light, leading to identification failures and reduced user experience.
Innovation Solution
An image sensing method that analyzes the first frame for overexposure areas, generates additional frames, and replaces overexposed pixel values with processed values to produce a third frame with clear image details, improving the completeness and accuracy of fingerprint images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed exposure time settings are used in optical fingerprint identification, then the device complexity is reduced, but image overexposure occurs due to varying finger widths, pressing angles, or strong environmental light, leading to identification failure
Solution Approach 1:
The patent implements dynamic exposure time adjustment by capturing multiple frames with different exposure times and selectively combining them. The system transitions from fixed exposure settings to adaptive exposure control, where the exposure time varies based on detected overexposure conditions in different regions of the fingerprint image.
Solution Approach 2:
The system changes the exposure time parameter dynamically by capturing a first frame with a first exposure time and a second frame with a second exposure time. Based on analysis of pixel values in the first frame, the system determines overexposure regions and adjusts exposure parameters for subsequent captures to optimize image quality.
2Reliability
If multiple fingerprints are registered to increase reliability, then the False Acceptance Rate decreases, but the time required for identification increases
Solution Approach 1:
The system performs self-correction by automatically detecting overexposure regions and replacing defective pixel values without requiring user intervention. This eliminates the need for users to repress their fingers due to identification failures, thereby reducing the time loss associated with multiple registration attempts while maintaining high security standards.
3Reliability
If the image sensing array captures a larger area to present complete fingerprint images, then the False Rejection Rate decreases, but the image processing complexity increases
Solution Approach 1:
The patent divides the fingerprint image into overexposure regions and non-overexposure regions based on pixel value analysis. By segmenting the image processing task, the system can apply different processing strategies to different regions, replacing only the overexposed pixel values while preserving the rest of the image, thus managing complexity effectively.
Solution Approach 2:
The system uses an intermediate processing step where pixel values from the first frame are analyzed to generate a mask identifying overexposure regions. This intermediate representation guides the selective replacement of pixel values using data from the second frame, simplifying the overall processing complexity while achieving complete fingerprint capture.
Data Source
AI summary
The present invention provides an image sensing device and an image sensing method. The image sensing device comprises an image sensing array and an image processing circuit. The image sensing array obtains a first frame for a test object, and the first frame comprises a plurality of first pixel values. The image processing circuit analyzes the first frame, and generate an overexposure area for the first pixel values greater than a first threshold in the first frame. Then, the image sensor array obtains a second frame for the overexposure area, and the second frame comprises a plurality of second pixel values. The image processing circuit performs a detection processing on all the first pixel values in the first frame, which retains the first pixel values outside of the overexposure area in the first frame, and replaces the first pixel values in the overexposure area with the second pixel values.