Method and device for forming a fingerprint representation

1. A method for forming a candidate fingerprint representation of a fingerprint of a user of an electronic device comprising a capacitive fingerprint sensor for sensing a fingerprint pattern, the method comprising the steps of:

acquiring a sequence of candidate fingerprint images comprising at least a first candidate fingerprint image acquired with a first imaging acquisition setting and a second candidate fingerprint image acquired with a second imaging acquisition setting different from the first imaging acquisition setting;

extracting a fingerprint feature set from each of the candidate fingerprint images, whereby a first fingerprint feature set is extracted from the first candidate fingerprint image and a second fingerprint feature set is extracted from the second candidate fingerprint image, the fingerprint features of each fingerprint feature set being extracted from the respective candidate fingerprint image according to a first selection criterion,

determining a first fingerprint feature representation set from said first fingerprint feature set, and a second fingerprint feature representation set from said second fingerprint feature set;

forming a candidate fingerprint representation from a combination of fingerprint feature representation sets comprising at least said first fingerprint feature representation set and said second fingerprint feature representation set.

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

selecting at least one fingerprint feature from said first fingerprint feature set based on a second selection criterion, and at least one fingerprint feature from said second fingerprint feature set based on said second selection criterion, wherein said fingerprint feature representation sets are determined from said selected fingerprint features.

3. The method according to claim 2 , wherein the second selection criterion is the same as the first selection criterion.

4. The method according to claim 2 , wherein the second selection criterion is different from the first selection criterion.

5. The method according to claim 1 , wherein at least one common fingerprint feature is comprised in both the first fingerprint feature set and in the second fingerprint feature set, wherein said method comprises:

forming said candidate fingerprint representation including a representation of said common fingerprint feature for each imaging acquisition setting.

6. The method according to claim 5 , comprising:

determining a geometrical transformation between the first fingerprint image and the second fingerprint image based on the common fingerprint feature, and

transforming the fingerprint feature representation set formed from said first fingerprint feature set according to the geometrical transformation before forming said candidate fingerprint representation.

7. The method according to claim 1 , wherein the first fingerprint feature set comprises at least one fingerprint feature being different from at least one fingerprint feature in said second fingerprint feature set.

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

discarding said sequence of candidate fingerprint images after said step of extracting fingerprint features for the respective fingerprint image.

9. The method according to claim 1 wherein any one of said imaging acquisition setting is a gain setting for the fingerprint sensor.

10. The method according to claim 1 , wherein any one of said imaging acquisition setting is a shift setting for the fingerprint sensor.

11. The method according to claim 1 , wherein any one of said imaging acquisition setting is a combination of a gain setting and a shift setting for the fingerprint sensor.

12. A method for authenticating a fingerprint of finger of a user of an electronic device comprising a capacitive fingerprint sensor, said method comprising the steps of claim 1 , and:

performing a fingerprint authentication procedure based on said candidate fingerprint representation.

13. A fingerprint sensing system, comprising:

a capacitive fingerprint sensor; and

a processor connected to said fingerprint sensor for:

controlling the fingerprint sensor to acquire a sequence of candidate fingerprint images comprising at least a first candidate fingerprint image acquired with a first imaging acquisition setting and a second candidate fingerprint image acquired with a second imaging acquisition setting different from the first imaging acquisition setting;

extracting a fingerprint feature set from each of the candidate fingerprint images, whereby a first fingerprint feature set is extracted from the first candidate fingerprint image and a second fingerprint feature set is extracted from the second candidate fingerprint image, the fingerprint features of each fingerprint feature set being extracted from the respective candidate fingerprint image according to a first selection criterion,

determining a first fingerprint feature representation set from said first fingerprint feature set, and a second feature representation set from said second fingerprint feature set;

forming a candidate fingerprint representation from a combination of fingerprint feature representation sets comprising at least said first fingerprint feature representation set and said second fingerprint feature representation set.

14. The fingerprint sensing system according to claim 13 , wherein said capacitive fingerprint sensor comprises a two-dimensional array of sensing elements configured to obtain a measure of the capacitive coupling between the finger and each sensing element.

15. An electronic device, comprising:

a fingerprint sensing system according to claim 13 , and a device controller for:

providing an authentication request for said finger to the fingerprint sensing system;

receiving said authentication signal from the fingerprint sensing system; and

performing at least one action if said authentication signal indicates authentication success.

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

17. Computer program product comprising a non-transitory computer readable medium having stored thereon computer program means for controlling an electronic device, the electronic device comprising a control unit, a capacitive fingerprint sensor, wherein the computer program product comprises:

code for controlling said capacitive fingerprint sensor to acquire a sequence of candidate fingerprint images comprising at least a first candidate fingerprint image acquired with a first imaging acquisition setting and a second candidate fingerprint image acquired with a second imaging acquisition setting different from the first imaging acquisition setting;

code for extracting a fingerprint feature set from each of the candidate fingerprint images, whereby a first fingerprint feature set is extracted from the first candidate fingerprint image and a second fingerprint feature set is extracted from the second candidate fingerprint image, said fingerprint features of each fingerprint feature set being extracted from the respective candidate fingerprint image according to a first selection criterion,

code for determining a first fingerprint feature representation set from said first fingerprint feature set, and a second feature representation set from said second fingerprint feature set;

code for forming a candidate fingerprint representation from a combination of fingerprint feature representation sets comprising at least said first fingerprint feature representation set and said second fingerprint feature representation set.