Fingerprint sensing system configured to determine if a finger contacts a fingerprint sensor
First Claim
1. Method performed by a fingerprint sensing system of determining if a finger contacts a fingerprint sensor of the fingerprint sensing system, comprising:
- capturing an image of an object contacting the fingerprint sensor;
determining an intensity for a plurality of pixels of the captured image;
computing, for each of said plurality of pixels of the captured image, a Hessian matrix where the components of the Hessian matrix consist of second-order derivatives of the pixel intensity in the captured image;
computing the square of the Hessian matrix;
computing a squared Fractional Anisotropy, FA, measure using eigenvalues of the computed squared Hessian matrix; and
determining from the squared FA measure if local pixel intensity variation is dominated by a single direction, in which case the object on the fingerprint sensor is considered to constitute a finger.
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Abstract
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.
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Citations
20 Claims
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1. Method performed by a fingerprint sensing system of determining if a finger contacts a fingerprint sensor of the fingerprint sensing system, comprising:
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capturing an image of an object contacting the fingerprint sensor; determining an intensity for a plurality of pixels of the captured image; computing, for each of said plurality of pixels of the captured image, a Hessian matrix where the components of the Hessian matrix consist of second-order derivatives of the pixel intensity in the captured image; computing the square of the Hessian matrix; computing a squared Fractional Anisotropy, FA, measure using eigenvalues of the computed squared Hessian matrix; and determining from the squared FA measure if local pixel intensity variation is dominated by a single direction, in which case the object on the fingerprint sensor is considered to constitute a finger. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 20)
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10. Fingerprint sensing system comprising a fingerprint sensor and a processing unit, the fingerprint sensing system being configured to determine if a finger contacts the fingerprint sensor of the fingerprint sensing system,
the fingerprint sensor being configured to: -
capture an image of an object contacting the fingerprint sensor; and the processing unit being configured to; determine an intensity for a plurality of pixels of the captured image; compute, for each of said plurality of pixels of the captured image, a Hessian matrix where the components of the Hessian matrix consist of second-order derivatives of the pixel intensity in the captured image; compute the square of the Hessian matrix; compute a squared Fractional Anisotropy, FA, measure using eigenvalues of the computed Hessian matrix; and determine from the squared FA measure if local pixel intensity variation is dominated by a single direction, in which case the object on the fingerprint sensor is considered to constitute a finger. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification