Suppressing impairment data in fingerprint images

1. A method of a fingerprint sensing system of suppressing impairment data present in an image captured by a fingerprint sensor of the fingerprint sensing system, comprising:

capturing a plurality of images of a fingerprint of a finger contacting the fingerprint sensor, the plurality of images comprising impairment data caused by impairments that the fingerprint sensor is subjected to, wherein the plurality of images are captured during normal user operation of an electronic device in which the fingerprint sensing system is arranged;

creating, from the plurality of captured images of the fingerprint, a composite image comprising the impairment data, wherein one or more images are repeatedly captured upon a user contacting the fingerprint sensor during normal user operation of the electronic device, wherein the composite image created from the plurality of captured images of the fingerprint is created and stored after a sufficient number of images of the fingerprint has been captured;

storing the composite image comprising the impairment data;

capturing at least one further image of a fingerprint of a finger contacting the fingerprint sensor;

processing the further captured image of a fingerprint with the stored composite image comprising the impairment data in order to at least partly suppress the impairment data in said further captured image of a fingerprint;

repeatedly capturing new images of the fingerprint, the images comprising impairment data;

creating, from the captured new images and the previously stored composite image comprising the impairment data, an updated image comprising the impairment data; and

storing the updated image comprising the impairment data, wherein the processing of the further captured image of a fingerprint is performed using the stored updated image comprising the impairment data in order to at least partly suppress the impairment data present in said further captured image of a fingerprint.

2. The method of claim 1 , wherein the processing of the further captured image of a fingerprint with the stored composite image comprising the impairment data comprises:

subtracting the stored composite image comprising the impairment data from the further captured image of a fingerprint.

3. The method of claim 1 , wherein the processing of the further captured image of a fingerprint with the stored composite image comprising the impairment data comprises:

dividing the impairment data present in the further captured image with the impairment data of the stored composite image.

4. The method of claim 1 , further comprising:

applying a small amount of fluid onto the finger of the user, and/or onto a surface of the sensing area of the fingerprint sensor before an image is captured.

5. The method of claim 1 , further comprising:

extracting a fingerprint from said further captured image of a fingerprint in which the impairment data has been suppressed;

comparing a fingerprint of the captured image of the finger with one or more authorised pre-stored fingerprint templates; and

authenticating a user if the extracted fingerprint of the captured image is considered to match one or more of the authorised pre-stored fingerprint templates.

6. The method of claim 1 , further comprising:

computing a confidence metric for the stored composite image comprising the impairment data, wherein in case at least a part of the stored composite image is considered to be unreliable as indicated by the computed confidence metric, said part is not utilized for suppressing impairment data present in the further captured image of a fingerprint.

7. The method of claim 6 , further comprising:

computing an updated confidence metric based on captured new images of the fingerprint; and

storing the updated confidence metric, wherein the stored updated confidence metric subsequently is taken into account when suppressing impairment data present in the further captured image of a fingerprint.

8. A fingerprint sensing system comprising a fingerprint sensor and a processing unit, the fingerprint sensing system being configured to suppress impairment data present in an image captured by the fingerprint sensor of the fingerprint sensing system,

the fingerprint sensor being configured to:

capture a plurality of images of a fingerprint of a finger contacting the fingerprint sensor, the plurality of images comprising impairment data caused by impairments that the fingerprint sensor is subjected to, wherein the plurality of images are captured during normal user operation of an electronic device in which the fingerprint sensing system is arranged;

the processing unit being configured to:

create, from the plurality of captured images of the fingerprint, a composite image comprising the impairment data, wherein one or more images are repeatedly captured upon a user contacting the fingerprint sensor during normal user operation of the electronic device, wherein the composite image created from the plurality of captured images of the fingerprint is created and stored after a sufficient number of images of the fingerprint has been captured;

store the composite image comprising the impairment data;

capture at least one further image of a fingerprint of a finger contacting the fingerprint sensor;

process the further captured image of a fingerprint with the stored composite image comprising the impairment data in order to at least partly suppress the impairment data in said further captured image of a fingerprint;

repeatedly capture new images of the fingerprint, the images comprising impairment data; and

the processing unit being configured to:

create, from the captured new images and the previously stored composite image comprising the impairment data, an updated image comprising the impairment data; and

store the updated image comprising the impairment data, wherein the processing of the further captured image of a fingerprint is performed using the stored updated image comprising the impairment data in order to at least partly suppress the impairment data present in said further captured image of a fingerprint.

9. A computer program product comprising a non-transitory computer readable medium, the computer readable medium having a computer program embodied thereon, the computer program comprising computer-executable instructions for causing a fingerprint sensing system to perform the method of claim 1 when the computer-executable instructions are executed on a processing unit included in the fingerprint sensing system.

10. An electronic device comprising the fingerprint sensing system of claim 8 .