Patent Application
20200364430
The present disclosure relates to a method and to a fingerprint sensing system for determining that a finger covers sensor area of a fingerprint sensor.
Various types of biometric systems are used more and more in order to provide for increased security and/or enhanced user convenience.
In particular, fingerprint sensing systems have been adopted in, for example, consumer electronic devices, thanks to their small form factor, high performance and user acceptance.
Fingerprint sensors can sometimes get activated prematurely, before the finger has made proper contact with the fingerprint sensor, or unintentionally, by a finger or other body part making contact with the fingerprint sensor by mistake, unnecessarily using up power and processing resources. It is preferable that a fingerprint sensor is only activated when a finger makes proper contact with it.
US 2015/0070137 discloses a method using electric field sensors for determining whether a sufficient part of the fingerprint sensor is covered by a finger, and whether the finger is in stable contact. It is determined whether a threshold number of subarrays from at least three of five regions of the fingerprint sensor have acquired finger stability data indicative of a finger. Then it is determined whether the finger is stable based upon whether the threshold number of sub-arrays indicates stability over successive data acquisitions.
It is an objective of the present invention to provide an improved way of determining whether a finger covers the whole of a sensor area of a fingerprint sensor.
It has now been realised that it may be desirable to further ensure that the whole of a sensor area of the fingerprint sensor detection surface is properly covered by a finger before performing an action, e.g. for navigation actions, where not only certain points of the fingerprint are studied. Navigation actions may e.g. include pressure detection indicative of a push/click on a button or link or the like, and movement detection indicative of steering a pointer or the like, e.g. of a graphical user interface, GUI. Also for fingerprint authentication it may be advantageous that the whole sensor area is covered by the finger before performing an authentication action.
According to an aspect of the present invention, there is provided a method of determining that a finger covers a sensor area of a fingerprint sensor. The method comprises, on a surface of the fingerprint sensor, receiving a finger having a fingerprint topography. The method also comprises, by means of the fingerprint sensor, acquiring an image of the fingerprint of the received finger. The method also comprises dividing an image area of the acquired image, corresponding to the sensor area of the fingerprint sensor, into a plurality of image regions, said regions partly overlapping each other and covering the whole image area. The method also comprises, based on image analysis of each of the plurality of image regions, determining that the finger covers the whole sensor area.
According to another aspect of the present invention, there is provided a computer program product comprising computer-executable components for causing a fingerprint sensing system to perform an embodiment of the method of the present disclosure when the computer-executable components are run on processing circuitry comprised in the fingerprint sensing system.
According to another aspect of the present invention, there is provided a fingerprint sensing system comprising a fingerprint sensor, processing circuitry, and data storage storing instructions executable by said processing circuitry whereby said fingerprint sensing system is operative to, on a surface of the fingerprint sensor, receive a finger having a fingerprint topography. The fingerprint sensing system is also operative to, by means of the fingerprint sensor, acquire an image of the fingerprint of the received finger. The fingerprint sensing system is also operative to divide an image area of the acquired image, corresponding to a sensor area of the fingerprint sensor, into a plurality of image regions, said regions partly overlapping each other and covering the whole image area. The fingerprint sensing system is also operative to, based on image analysis of each of the plurality of image regions, determine that the finger covers the whole sensor area.
According to another aspect of the present invention, there is provided an electronic device comprising an embodiment of the fingerprint sensing system of the present disclosure, and a device control unit configured to interact with the fingerprint sensing system.
If it is only checked that a few separate parts of the sensor area are covered by a finger, nothing is known about whether the finger is covering also the sensor area between said parts. By dividing the image area, corresponding to the sensor area, into image regions which together cover the whole image area, the risk of not detecting non-covered parts of the sensor area is reduced. However, a non-covered part of the sensor area which extends over two adjacent, but not overlapping, image regions of the corresponding image area may still not trigger detection of the non-covered part since the non-covered part is divided between two or more regions, each only being affected to a relatively small degree. The solution of the present invention is to use overlapping regions, whereby there is increased probability that at least one of the regions is affected to such a degree that detection of the non-covered part is made by image analysis.
It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of “first”, “second” etc. for different features/components of the present disclosure are only intended to distinguish the features/components from other similar features/components and not to impart any order or hierarchy to the features/components.
Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:
Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.
The fingerprint sensor 3 may operate according to any sensing technology. For instance, the finger print sensor may be a capacitive, optical or ultrasonic sensor. Herein, a capacitive fingerprint sensor, which may be preferred for some applications, is discussed as an example. The fingerprint sensor may comprise a two-dimensional array of fingerprint sensing elements, each corresponding to a pixel of the image outputted by the fingerprint sensor, the pixel e.g. being represented by a grey-scale value. The fingerprint sensor may be located at a side of the display stack 2, outside of the display area of the display 12, as shown in
Referring to the block diagram in
Accordingly (see also
In some embodiments, the fingerprint sensor 3 is a capacitive, ultrasonic or optical fingerprint sensor, e.g. a capacitive fingerprint sensor.
In some embodiments, the fingerprint sensor 3 is covered by a glass layer, e.g. by means of a cover glass or a glass coating, e.g. protecting the sensing elements and providing the detection surface of the fingerprint sensor.
The data storage 20 may be regarded as a computer program product 20 comprising computer-executable components 21 for causing the fingerprint sensing system 13 to perform an embodiment of the method of the present disclosure when the computer-executable components are run on processing circuitry 16 comprised in the fingerprint sensing system. Additionally, any mobile or external data storage means, such as a disc, memory stick or server may be regarded as such a computer program product.
The electronic device also comprises a device control unit 18 configured to control the electronic device 1 and to interact with the fingerprint sensing system 13. The electronic device also comprises a battery 22 for providing electrical energy to the various components of the electronic device 1.
Although not shown in
The electronic device 1 may be any electrical device or user equipment (UE), mobile or stationary, e.g. enabled to communicate over a radio channel in a communication network, for instance but not limited to e.g. mobile phone, tablet computer, laptop computer or desktop computer.
The electronic device 1 may thus comprise an embodiment of the fingerprint sensing system 13 discussed herein, and a device control unit 18 configured to interact with the fingerprint sensing system.
In some embodiments, the device control unit 18 is configured to interact with the fingerprint sensing system 13 such that a navigation input of the finger 5 detected by the fingerprint sensing system is detected as a command for control of the electronic device 1 by the device control unit.
As a finger 5 contacts a detection surface of the fingerprint sensor 3, the fingerprint sensor is activated to by means of the fingerprint image acquisition circuitry 14 acquire an image n, or a time-sequence 30 of images n to m (herein also denoted n . . . m) as illustrated in
An advantage with overlapping regions r is illustrated by means of
In some embodiments, after the determining S4 that the finger 5 covers the whole sensor area 42, a navigation input from the finger is detected S5. The navigation input may e.g. be based on gesture recognition, which may for instance facilitate navigation in e.g. a menu or the like of a GUI. The detecting S5 of the navigation input may comprise detecting a pressure of the finger 5 against the sensor area 42 or detecting a movement of the finger 5 relative to the sensor area 42. As mentioned above, navigation actions may e.g. include pressure detection indicative of a selection, push/click on a button or link or 30 the like, and movement detection indicative of steering a pointer or the like, e.g. of a GUI presented by the display stack 2. In other embodiments, an authentication operation may be triggered by the determining S4 that the finger 5 covers the whole sensor area 42.
In some embodiments, the determining S4 that the finger 5 covers the whole sensor area 42 comprises comparing an average intensity value imean of the image area 41 with at least one intensity value it of each of the image regions r. The average intensity value imean of the image area may e.g. be an average grey-scale value of all pixels in the image area, or of groups of pixels in the image area. The at least one intensity value it of each of the image regions r may e.g. be an average intensity value, a maximum intensity value or a minimum intensity value, e.g. of grey-scale values of all pixels in the image region, or of groups of pixels in the image region, preferably a minimum intensity value ir,min of each image region.
Then it can be determined S45 that the finger covers the sensor area when the FCS is below a predetermined threshold tFCS, i.e. FCS<tFCS. The FCS may for example be within the range of 0.5-0.9 when the finger covers the whole sensor area, e.g. the fingerprint topography is in contact with the detection surface over the whole sensor area. Thus, the threshold tFCS may conveniently be at least 0.9, e.g. within the range of 0.95-1.1
In some embodiments, the sensor area 42 covers the whole detection surface of the fingerprint sensor 3, i.e. the sensor area 42 is not a sub-area of the detections surface, whereby essentially all the sensing elements of the fingerprint sensor 3 are used to form pixels in the image area 41. In some other embodiments, the sensor area 42 covers only a part of the fingerprint sensor 3. It may e.g. be enough that the sensor area 42 covers only a part, such as 30, 50 or 70%, of the detection surface of the fingerprint sensor 3, e.g. depending on the size and/or resolution of the fingerprint sensor 3, in order to be enabled for an action, such as authentication and/or navigation as discussed herein.
In some embodiments, the determining S4 that the finger 5 covers the whole sensor area 42 comprises determining that the finger is in contact with the surface of the fingerprint sensor 3 over the whole sensor area. Although some sensor technologies, e.g. capacitive, may allow for fingerprint sensing also when the fingerprint topography hovers just above the detection surface, it may be convenient, e.g. for obtaining a stable image n, that the fingerprint topography, typically the ridges thereof, is in direct physical contact with the detection surface. The detection surface may be provided by e.g. a cover glass or glass coating of the fingerprint sensor 3, protecting the fingerprint sensing elements.
As also discussed with reference to
The image regions r may have any shape or size, but in some embodiments each of the plurality of image regions r has size of at least 8×8 pixels of the acquired image n. In some embodiments, each of the plurality of image regions r corresponds to a sensor region, being a sub-area of the sensor area 42, having a size of at least 0.48 mm times 0.48 mm of the sensor area.
As previously mentioned, the acquired image n, e.g. any image n . . . m of an acquired time-sequence 30 of images, may be a grey-scale image.
The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1751086-8 | Sep 2017 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2018/050885 | 9/3/2018 | WO | 00 |
