Fingerprint Sensor Contact Detection Using Pixel Curvature Analysis
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Solution Overview
Problem
Fingerprint sensors that do not require physical activation can be unintentionally activated by objects other than fingers, leading to unnecessary power consumption and incorrect locking modes when carried in pockets or bags.
Innovation Solution
A method that captures an image of an object contacting the sensor, determines pixel intensity variations, estimates local curvatures, and uses the Fractional Anisotropy measure to differentiate between finger and non-finger contacts by analyzing the dominance of intensity variation in a single direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the fingerprint sensor is activated upon contact with any object, then the sensor can detect fingerprints without physical pressing, but the sensor may be unintentionally activated by non-finger objects such as cloth, coins, or keys
Solution Approach 1:
The system performs preliminary analysis of the contacted object's characteristics (curvature, texture, material properties) before activating fingerprint recognition. This preliminary action distinguishes between finger and non-finger objects, preventing false activations while maintaining contactless operation
Solution Approach 2:
The patent introduces intermediate analysis steps between contact detection and fingerprint recognition activation. These intermediate steps analyze object properties as a mediator to determine whether to proceed with full fingerprint recognition, thereby filtering out false activations
2Measurement precision
If the sensor captures and processes images of all contacted objects, then no finger contact is missed, but unnecessary power is consumed processing non-finger objects
Solution Approach 1:
The system performs partial image processing only on suspected finger contacts. Instead of fully processing all contacted objects, it applies a lightweight preliminary analysis and only activates full fingerprint recognition processing when a finger is detected, thereby reducing unnecessary energy consumption
Solution Approach 2:
The image processing is segmented into multiple stages: initial contact detection, preliminary object classification, and full fingerprint recognition. This segmentation allows the system to process only those images that require full analysis, conserving battery power on non-finger contacts
3Speed
If the sensor is constantly monitoring for contact, then immediate detection is achieved, but the device complexity increases
Solution Approach 1:
Instead of continuous monitoring, the system uses periodic sampling at intervals sufficient to detect user intent. This periodic approach maintains fast detection capability while reducing the computational burden and system complexity associated with constant monitoring
Data Source
AI summary
The invention relates to a method performed by a fingerprint sensing system of determining if a finger contacts a fingerprint sensor of the system, and a fingerprint sensing system performing method. In a first aspect of the invention, a method performed by a fingerprint sensing system is provided for determining if a finger contacts a fingerprint sensor of the fingerprint sensing system. The method comprises capturing an image of an object contacting the fingerprint sensor, determining an intensity for a plurality of pixels of the captured image, estimating local curvatures of pixel intensity variation in the captured image, and determining from the estimated local curvatures if local pixel intensity variation is dominated by a single direction, in which case the object on the sensor is considered to constitute a finger.