The present invention generally relates to authenticating a user of an electronic device comprising a capacitive fingerprint sensor and an optical sensor arranged side-by-side with the capacitive fingerprint sensor. In accordance with the present invention a first image of at least a first portion o
The present invention generally relates to authenticating a user of an electronic device comprising a capacitive fingerprint sensor and an optical sensor arranged side-by-side with the capacitive fingerprint sensor. In accordance with the present invention a first image of at least a first portion of an object is acquired using the capacitive fingerprint sensor and an optical image of at least a second portion of the object is acquired using the optical sensor, the optical image and the first image being representative of neighboring portions of the object. An edge portion of the first image is matched with at least an edge portion of the optical image, where the edge portions represent the object at the border between the capacitive fingerprint sensor and the optical sensor. When there is a match, a fingerprint authentication procedure may be performed.
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1. A method for authenticating a user of an electronic device comprising: a capacitive fingerprint sensor comprising an array of sensing elements for sensing a fingerprint pattern, each sensing element having a sensing structure arranged in a sensing structure plane, said capacitive fingerprint sens
1. A method for authenticating a user of an electronic device comprising: a capacitive fingerprint sensor comprising an array of sensing elements for sensing a fingerprint pattern, each sensing element having a sensing structure arranged in a sensing structure plane, said capacitive fingerprint sensor being configured to obtain a capacitive image of a first portion of a user's finger, andan optical sensor arranged side-by-side with said capacitive fingerprint sensor, said optical sensor comprising an array of optical sensor units arranged adjacent to said array of sensing structures in said sensing structure plane, said optical sensor being configured to obtain an optical image of a second portion of said user's finger, said second portion and said first portion being neighboring portions, wherein said method comprising the steps of: acquiring, using the capacitive fingerprint sensor, a first image of at least a first portion of an object;acquiring, using the optical sensor, a optical image of at least a second portion of said object, said optical image and said first image being representative of neighboring portions of said object;matching an edge portion of the first image with at least an edge portion of said optical image, the edge portion of the first image and the edge portion of the optical image representing the object at the border between the capacitive fingerprint sensor and the optical sensor, wherein when there is a match,performing a fingerprint authentication procedure based on at least one of the first image and the optical image, and a plurality of fingerprint enrolment templates. 2. The method according to claim 1, further comprising: acquiring, using the optical sensor, a set of optical images comprising at least a first optical image acquired at a first wavelength range and a second optical image acquired at a second wavelength range different from the first wavelength range; wherein said step of matching of the edge portion of the first image with at least an edge portion of said optical image comprises:matching said edge portion of said first image with an edge portion of each of the optical images in the set of optical images. 3. The method according to claim 2, further comprising: normalizing said set of optical images with respect to one of the optical images in the set of optical images. 4. The method according to claim 2, further comprising: determining a fingerprint feature location in the edge portion of said first image;based on the fingerprint feature location, determining the expected feature location of the fingerprint feature in the optical images of the set of optical images;comparing representations of the fingerprint feature at the expected feature location in the optical images to each other, the representations being formed from the optical images acquired at different wavelengths, whereinbased on the comparison determine that there is a match, whereby a fingerprint authentication procedure may be performed. 5. The method according to claim 4, further comprising: determining a set of ridge locations and a set of valley locations in the edge portion of said first image;based on the ridge and valley positions in the first image, determining a set of expected ridge locations and a set of expected valley locations in each of the optical images acquired at different wavelengths;based on output signal levels at said expected ridge locations and expected valley locations in the optical images, for each optical image acquired at different wavelengths: determining an average ridge signal level for said set of expected ridge locations in the optical image, anddetermining an average valley signal level for said set of expected valley locations in the optical image,calculating a normalized average ridge signal level, said normalization being with respect to one of the determined average ridge signals at one of the wavelengths, andcalculating a normalized average valley signal level, said normalization being with respect to said one of the determined average valley signals at said one of the wavelengths;for each of said different wavelengths, compare said normalized average ridge signal level to said normalized average valley signal level, whereinbased on the comparison, determining that there is a match between the edge portion of the first image and the edge portion of each of said optical images. 6. The method according to claim 4, comprising: determining a set of valley locations in the edge portion of said first image;based on the valley location in the first image, determining a set of expected valley locations in the optical images acquired at different wavelengths;based on output signal levels at said expected valley locations in the optical images, for each optical image acquired at different wavelengths: determining a first average valley signal level for a first subset of said set of expected valley locations in the optical image,determining a second average valley signal level for a second subset of said set of expected valley locations in the optical image; andcalculating a first normalized average valley signal level for the first average valley signal, said normalization being with respect to the respective one of the determined average valley signals at one of the wavelengths,calculating a second normalized average valley signal level for the second average valley signal, said normalization being with respect to the respective one of the determined average valley signals at said one of the wavelengths,for each of said different wavelengths, comparing the first normalized valley ridge signal level to the second normalized average valley signal level, whereinbased on the comparison, determining that there is a match between the edge portion of the first image and the edge portion of each of said optical images. 7. The method according to claim 4, further comprising: determining a set of ridge locations in the edge portion of said first image;based on the ridge location in the first image, determining a set of expected ridge locations in the optical images acquired at different wavelengths;based on output signal levels at said expected ridge locations in the optical images, for each optical image acquired at different wavelengths: determining a first average ridge signal level for a first subset of said set of expected ridge locations in the optical image,determining a second average ridge signal level for a second subset of said set of expected ridge locations in the optical image; andcalculating a first normalized average ridge signal level for the first average ridge signal, said normalization being with respect to the respective one of the determined average ridge signals at one of the wavelengths, andcalculating a second normalized average ridge signal level for the second average ridge signal, said normalization being with respect to the respective one of the determined average ridge signals at said one of the wavelengths;for each of said different wavelengths, comparing the first normalized ridge signal level to the second normalized average ridge signal level, whereinbased on the comparison, determining that there is a match between the edge portion of the first image and the edge portion of each of said optical images. 8. The method according to claim 1, wherein said matching comprises: comparing a pattern in said edge portion of said first image with a pattern in said edge portion of each of at least one optical image, whereindetermining, based on said comparing of patterns, if stitching of the first image with each of the at least one optical image is possible, whereinwhen said stitching is successful, determining that there is a match between the edge portion of the first image and the edge portion of each of said at least one optical image. 9. The method according to claim 8, wherein when stitching is successful: performing said fingerprint authentication procedure based on the combined verification image formed by stitching the first image with one of the at least one optical image, and said plurality of fingerprint enrolment templates, wherein the fingerprint enrolment templates are based on stitched capacitive and optical enrolment images. 10. The method according to claim 1, wherein said matching comprises: determining first output signal levels from sensing elements of said capacitive fingerprint sensor neighboring the border with the optical sensor configured to acquire the edge portion of the first image;determining second output signal levels from optical sensor units neighboring said sensing elements of said capacitive fingerprint at the border between the capacitive fingerprint sensor and the optical sensor, said optical sensor units being configured to acquire the edge portion of the optical image,determining a derivative of said output signal levels across from the edge portion of the first image to the optical image or across from the optical image to the edge portion of the first image, wherein,when the magnitude of the derivative is less than a threshold value, determining that there is a match between the edge portion of the first image and the edge portion of said optical image. 11. The method according to claim 10, further comprising: before determining said derivatives, normalizing said first output signal levels with respect to said second output signal levels or normalizing said second output signal levels with respect to said first output signal levels. 12. The method according to claim 1, wherein said capacitive fingerprint sensor is a two-dimensional sensor and said optical sensor is a one-dimensional sensor. 13. Fingerprint sensing system comprising: a capacitive fingerprint sensor comprising an array of sensing elements for sensing a fingerprint pattern, each sensing element having a sensing structure arranged in a sensing structure plane, said capacitive fingerprint sensor being configured to obtain a capacitive fingerprint image of a first portion of said user's finger,an optical sensor comprising an array of optical sensor units arranged adjacent to said array of sensing structures in said sensing structure plane, said optical sensor being configured to obtain an optical image of a second portion of said user's finger, said second portion and said first portion being neighboring portions,said fingerprint sensing system being configured to: acquire, using the capacitive fingerprint sensor, a first image of at least a first portion of an object;acquire, using the optical fingerprint sensor, a optical image of at least a second portion of said object, said optical image and said first image being representative of neighboring portions of said object;providing said first image and said optical image to a control unit configured to: match an edge portion of the first image with at least an edge portion of said optical image, the edge portion of the first image and the edge portion of the optical image representing the border between the capacitive fingerprint sensor and the optical sensor, wherein when there is a match,perform a fingerprint authentication procedure based on at least one of the first image and the optical image, and a plurality of fingerprint enrolment templates. 14. The fingerprint sensing system according to claim 13, wherein said array of sensing elements of said capacitive fingerprint sensor is a two-dimensional array and said array of optical sensor units of said optical sensor is a one-dimensional array arranged along an edge of said array of sensing elements. 15. The fingerprint sensing system according to 13, wherein said array of optical sensor units of said optical sensor is arranged such that the array of sensing elements of said capacitive fingerprint sensor is surrounded by optical sensor units in the sensing structure plane. 16. The fingerprint sensing system according to claim 13, wherein said optical sensor arrangement comprises a light-emitting device configured to illuminate said object, wherein said optical sensor units are configured to detect said optical image in response to said illumination by said light-emitting device. 17. The fingerprint sensing system according to claim 13, wherein said optical sensor is configured to obtain said optical image by reflection spectroscopy or transmission spectroscopy. 18. The fingerprint sensing system according to claim 13, wherein said optical sensor units comprises photo diodes. 19. The fingerprint sensing system according to claim 13, configured to perform the steps claim 1. 20. An electronic device, comprising: a fingerprint sensing system according to claim 13, and said control unit, wherein said control unit is configured to: control the capacitive fingerprint sensor to acquire a first image of at least a portion of an object;control the optical fingerprint sensor to acquire a optical image of at least a portion of said object, said optical image and said first image being representative of neighboring portions of said object;match an edge portion of the first image with at least an edge portion of said optical image, the edge portion of the first image and the edge portion of the optical image representing the border between the capacitive fingerprint sensor and the optical sensor, wherein when there is a match,perform a fingerprint authentication procedure based on at least one of the first image and the optical image, and a plurality of fingerprint enrolment templates. 21. The electronic device according to claim 20, wherein the electronic device is a mobile phone. 22. 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 comprising an array of sensing elements for sensing a fingerprint pattern each sensing element having a sensing structure arranged in a sensing structure plane, said capacitive fingerprint sensor being configured to obtain a capacitive fingerprint image of a first portion of said user's finger; andan optical sensor comprising an array of optical sensor units arranged adjacent to said array of sensing structures in said sensing structure plane, said optical sensor being configured to obtain an optical image of a second portion of said user's finger, said second portion and said first portion being neighboring portions,wherein the computer program product comprises: code for controlling the capacitive fingerprint sensor to acquire a first image of at least a portion of an objectcode for controlling the optical fingerprint sensor to acquire a optical image of at least a portion of said object, said optical image and said first image being representative of neighboring portions of said object;code for matching an edge portion of the first image with at least an edge portion of said optical image, the edge portion of the first image and the edge portion of the optical image representing the border between the capacitive fingerprint sensor and the optical sensor, andcode for, when there is a match, performing a fingerprint authentication procedure based on at least one of the first image and the optical image, and a plurality of fingerprint enrolment templates.
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