Capacitive Fingerprint Sensor Wet Finger Image Acquisition
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Solution Overview
Problem
Capacitive fingerprint sensors face challenges in acquiring high-quality images from wet or sweaty fingers, as the conductivity of the skin makes it difficult to distinguish between ridges and valleys, resulting in low-contrast inverted images that are not easily recognizable by software algorithms.
Innovation Solution
The method involves using a fingerprint sensing system that applies a specific 'sweaty finger' sensor setting as soon as the finger contacts the sensor, followed by a 'normal' sensor setting, with sensitivity levels adjusted accordingly, and evaluates the acquired images based on a quality metric to select the best image for processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard capacitive sensing technique is used for wet fingers, then the sensor captures high signal from both valleys and ridges, but the resulting image has low contrast and inverted appearance making it difficult to separate ridges from valleys
Solution Approach 1:
The patent applies dynamic adjustment of sensor sensitivity settings based on detected finger humidity levels. The system transitions from a static sensitivity setting to a dynamic one that adapts to wet or dry finger conditions, allowing optimal signal capture while maintaining pattern distinguishability through real-time parameter adjustment
Solution Approach 2:
The patent changes the sensitivity parameter of the capacitive sensor based on finger humidity detection. By adjusting the sensitivity setting according to whether the finger is wet or dry, the system optimizes the balance between signal strength and pattern contrast, resolving the contradiction between detecting high signals and maintaining image quality
2Measurement precision
If multiple images are captured and stitched together to overcome sweaty finger problems, then image quality may be improved, but additional computational steps increase processing complexity and device constraints
Solution Approach 1:
The patent performs preliminary detection of finger humidity levels before capturing the fingerprint image. By detecting the wetness condition in advance and adjusting the sensitivity setting accordingly, the system prevents the need for post-capture image stitching and processing, thereby reducing computational complexity while maintaining image quality
Solution Approach 2:
The system uses the fingerprint sensor itself to detect finger humidity levels and automatically adjusts its sensitivity setting based on this self-detected information. This self-service approach eliminates the need for external processing systems to analyze and stitch multiple images, reducing overall device complexity
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 improves the acquisition of fingerprint images from sweaty fingers by capturing images early before sweat obscures the pattern, enhancing image quality and reducing the need for additional computational steps, thus increasing user convenience.
Implementation Method 1
All capacitive fingerprint sensors provide an indicative measure of the capacitance between several sensing elements and a finger placed on the surface of the fingerprint sensor
Implementation Method 2
For wet fingers, where water or saline (sweat) fill the valleys, the problem is mainly that the saline is even more conductive than the stratum corneum
Data Source
AI summary
The present invention generally relates to a method for acquiring a fingerprint image using a fingerprint sensing system. Advantages with the invention include improved acquisition of fingerprint images of e.g. wet (sweaty) fingers. The invention also relates to a corresponding fingerprint sensing system and to a computer program product.