Method and fingerprint sensing system for acquiring a fingerprint image

1. A method of acquiring a fingerprint image of a finger by means of a fingerprint sensing system comprising a fingerprint sensor and processing circuitry connected to the fingerprint sensor, wherein the method comprises:

receiving an indication of the finger contacting the fingerprint sensor;

applying a first fingerprint image acquisition setting for the fingerprint sensor, the first fingerprint image acquisition setting including a first sensitivity level for the fingerprint sensor;

acquiring, subsequent to receiving the indication of the finger contacting the fingerprint sensor, a first fingerprint image using the first fingerprint image acquisition setting;

applying, subsequent to acquiring the first fingerprint image, a second fingerprint image acquisition setting for the fingerprint sensor, the second fingerprint image acquisition setting including a second sensitivity level for the fingerprint sensor, the second sensitivity level being in comparison higher than the first sensitivity level;

acquiring, subsequent to applying the second fingerprint image acquisition setting, a first fingerprint image using the second fingerprint image acquisition setting;

evaluating the acquired fingerprint images based on a quality metric, and

selecting at least one of the acquired fingerprint images satisfying the quality metric,

wherein the second fingerprint image acquisition setting is adapted for acquiring a finger with low or normal level of humidity, and the first fingerprint image acquisition setting is adapted for acquiring a finger with an in comparison higher level of humidity.

2. The method according to claim 1 , further comprising:

acquiring, subsequent to acquiring the first fingerprint image using the first fingerprint image acquisition setting, a second fingerprint image using the first fingerprint image acquisition setting.

3. The method according to claim 1 , wherein evaluating comprises examining a spatial intensity variation in the fingerprint images.

4. The method according to claim 1 , wherein evaluating comprises examining at least one of an image saturation and a histogram width in the fingerprint images.

5. The method according to claim 1 , further comprising:

applying, subsequent to acquiring the first fingerprint image using the second fingerprint image acquisition setting, a third fingerprint image acquisition setting for the fingerprint sensor, the third fingerprint image acquisition setting being based on the evaluation of the first fingerprint image acquired using the second fingerprint image acquisition setting; and

acquiring a first fingerprint image using the third fingerprint image acquisition setting.

6. The method according to claim 2 , wherein the second fingerprint image acquired using the first fingerprint image acquisition setting is acquired a predetermined time subsequent to acquiring the first fingerprint image acquired using the first fingerprint image acquisition setting, the predetermined time being between about 5-60 ms, preferably between 15-60 ms.

7. The method according to claim 1 , further comprising:

post-processing the at least one fingerprint image satisfying the predetermined quality metric.

8. The method according to claim 1 , further comprising:

combining at least two of the acquired fingerprint images.

9. The method according to claim 1 , further comprising:

retrieving a signal indicative of an environmental condition that may affect a property of the finger; and

selecting the first fingerprint image acquisition setting based on the environmental condition.

10. A fingerprint sensing system, comprising:

a fingerprint sensor;

a memory; and

processing circuitry connected to the fingerprint sensor for:

receiving an indication of the finger contacting the fingerprint sensor;

applying a first fingerprint image acquisition setting for the fingerprint sensor, the first fingerprint image acquisition setting including a first sensitivity level for the fingerprint sensor;

acquiring, subsequent to receiving the indication of the finger contacting the fingerprint sensor, a first fingerprint image using the first fingerprint image acquisition setting;

applying, subsequent to acquiring the first fingerprint image, a second fingerprint image acquisition setting for the fingerprint sensor, the second fingerprint image acquisition setting including a second sensitivity level for the fingerprint sensor, the second sensitivity level being in comparison higher than the first sensitivity level;

acquiring, subsequent to applying the second fingerprint image acquisition setting, a first fingerprint image using the second fingerprint image acquisition setting;

evaluating the acquired fingerprint images based on a quality metric, and

selecting at least one of the acquired fingerprint images satisfying the quality metric,

wherein the second fingerprint image acquisition setting is adapted for acquiring a finger with low or normal level of humidity, and the first fingerprint image acquisition setting is adapted for acquiring a finger with an in comparison higher level of humidity.

11. The fingerprint sensing system according to claim 10 , wherein the fingerprint sensor is a capacitive fingerprint sensor.

12. An electronic device comprising:

the fingerprint sensing system according to claim 10 ; and

a device controller for:

performing an authentication of the finger based on the at least one selected fingerprint image, and

performing at least one action only if the authentication indicates an authentication success.

13. The electronic device according to claim 12 , further comprising at least one sensor for sensing a local environment of the electronic device, the controller being configured to provide a signal indicative of an environmental condition that may affect a property of the finger to the fingerprint sensing system.

14. The electronic device according to claim 13 , wherein the at least one sensor includes at least one sensor selected from a group comprising a temperature sensor and a humidity sensor.

15. The portable electronic device according to claim 12 , wherein the portable electronic device is a mobile phone.

16. A computer program product comprising a non-transitory computer readable medium having stored thereon computer program means for controlling a portable electronic device, the portable electronic device comprising a fingerprint sensing system including a fingerprint sensor and processing circuitry, the fingerprint sensing system adapted for acquiring a fingerprint image of a finger, wherein the computer program product comprises:

code for receiving an indication of the finger contacting the fingerprint sensor;

code for applying a first fingerprint image acquisition setting for the fingerprint sensor, the first fingerprint image acquisition setting including a first sensitivity level for the fingerprint sensor;

code for acquiring, subsequent to receiving the indication of the finger contacting the fingerprint sensor, a first fingerprint image using the first fingerprint image acquisition setting;

code for applying, subsequent to acquiring the first fingerprint image, a second fingerprint image acquisition setting for the fingerprint sensor, the second fingerprint image acquisition setting including a second sensitivity level for the fingerprint sensor, the second sensitivity level being in comparison higher than the first sensitivity level;

code for acquiring, subsequent to applying the second fingerprint image acquisition setting, a first fingerprint image using the second fingerprint image acquisition setting;

code for evaluating the acquired fingerprint images based on a quality metric, and

code for selecting at least one of the acquired fingerprint images satisfying the quality metric, wherein the second fingerprint image acquisition setting is adapted for acquiring a finger with low or normal level of humidity, and the first fingerprint image acquisition setting is adapted for acquiring a finger with an in comparison higher level of humidity.