WO2021243986A1 - 屏下式指纹感测装置 - Google Patents

屏下式指纹感测装置 Download PDF

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Publication number
WO2021243986A1
WO2021243986A1 PCT/CN2020/132935 CN2020132935W WO2021243986A1 WO 2021243986 A1 WO2021243986 A1 WO 2021243986A1 CN 2020132935 W CN2020132935 W CN 2020132935W WO 2021243986 A1 WO2021243986 A1 WO 2021243986A1
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Prior art keywords
finger
image sensor
under
display
sensing device
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PCT/CN2020/132935
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English (en)
French (fr)
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林冠仪
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神盾股份有限公司
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Publication of WO2021243986A1 publication Critical patent/WO2021243986A1/zh

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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06VIMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12Fingerprints or palmprints
    • G06V40/13Sensors therefor
    • G06V40/1318Sensors therefor using electro-optical elements or layers, e.g. electroluminescent sensing
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06VIMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12Fingerprints or palmprints
    • G06V40/1347Preprocessing; Feature extraction
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06VIMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12Fingerprints or palmprints
    • G06V40/1382Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger
    • G06V40/1388Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger using image processing
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06VIMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12Fingerprints or palmprints
    • G06V40/1382Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger
    • G06V40/1394Detecting the live character of the finger, i.e. distinguishing from a fake or cadaver finger using acquisition arrangements

Definitions

  • the invention relates to a sensing device, in particular to an under-screen fingerprint sensing device.
  • the capacitive fingerprint sensor originally placed on the front of the electronic device is no longer applicable, and needs to be changed to be placed on the side or back of the electronic device.
  • the fingerprint sensor placed on the side or the back has inconveniences in use, so an under-screen fingerprint sensor has been developed.
  • Under-screen fingerprint sensors can be roughly divided into optical fingerprint sensors and ultrasonic fingerprint sensors. Among them, optical fingerprint sensors are cheaper and more suitable for mass production. Since fingerprint sensing is critical to the security of the user's personal data, it is still necessary to develop an anti-spoofing function. For example, a person who wants to steal personal data may collect a user's fingerprint in the environment and make a fake finger with the fingerprint, and then press the electronic device with the fake finger to achieve successful fingerprint recognition and unlock. Therefore, it is necessary to develop a fingerprint sensor that can recognize fake fingers instead of real fingers to further improve the security of the user's personal data.
  • the present invention is directed to an under-screen fingerprint sensing device, which can identify a real finger and a fake finger.
  • An embodiment of the present invention provides an under-screen fingerprint sensing device for matching with a display.
  • the display emits illuminating light, and the illuminating light is transmitted to the finger pressing on the display, and the finger reflects the illuminating light into fingerprint information carrying the finger Signal light.
  • the under-screen fingerprint sensing device includes an image sensor and a controller.
  • the image sensor is arranged under the display, and the signal light penetrates the display to form a fingerprint image on the image sensor.
  • the controller is electrically connected to the image sensor to process the fingerprint image sensed by the image sensor, and make the inner product of the grayscale values and Haar-like features on the two axes of the fingerprint image in different directions, and borrow This judges whether the fingerprint image comes from a real finger or a fake finger.
  • An embodiment of the present invention provides an under-screen fingerprint sensing device for matching with a display.
  • the display emits illuminating light, and the illuminating light is transmitted to the finger pressing on the display, and the finger reflects the illuminating light into fingerprint information carrying the finger Signal light.
  • the under-screen fingerprint sensing device includes an image sensor and a controller.
  • the image sensor is arranged under the display, and the signal light penetrates the display to form a fingerprint image on the image sensor.
  • the controller is electrically connected to the image sensor and used for processing the fingerprint image sensed by the image sensor.
  • the controller is used to calculate the average gray level of the central area of the fingerprint image and the respective average gray levels of the two peripheral areas on both sides of the central area, and thereby determine whether the fingerprint image is from a real finger or a fake finger.
  • An embodiment of the present invention provides an under-screen fingerprint sensing device for matching with a display.
  • the display emits illuminating light, and the illuminating light is transmitted to the finger pressing on the display, and the finger reflects the illuminating light into fingerprint information carrying the finger Signal light.
  • the under-screen fingerprint sensing device includes an image sensor and a controller.
  • the image sensor is arranged under the display, and the signal light penetrates the display to form a fingerprint image on the image sensor.
  • the controller is electrically connected to the image sensor and used for processing the fingerprint image sensed by the image sensor.
  • the controller is used to internally product the grayscale values on the two axes of the fingerprint image with different directions and the Haar feature to obtain the first result.
  • the controller is used to calculate the average gray scale of the central area of the fingerprint image and the respective gray scale averages of the two peripheral areas on both sides of the central area to obtain the second result.
  • the controller is used to synthesize the first result and the second result to determine whether the fingerprint image is from a real finger or a fake finger.
  • the controller performs inner product of the grayscale values on the two axes of the fingerprint image in different directions and the Haar feature, and/or calculates the central area of the fingerprint image The average gray level of, and the average gray levels of the two peripheral areas on both sides of the central area, to determine whether the fingerprint image comes from a real finger or a fake finger. Therefore, the under-screen fingerprint sensing device of the embodiment of the present invention can achieve an anti-spoofing effect in fingerprint sensing, thereby improving the security of the user's personal data.
  • FIG. 1 is a schematic cross-sectional view of an electronic device according to an embodiment of the invention.
  • Fig. 2A shows a situation in which the illumination light with the P polarization direction in Fig. 1 is reflected by the finger;
  • Fig. 2B shows a situation in which the illumination light with the S polarization direction in Fig. 1 is reflected by the finger;
  • Fig. 3 is a distribution curve of the reflectance and transmittance of the illuminating light at the interface of the finger and the glass cover of Fig. 1 with respect to the incident angle of the interface;
  • Fig. 4A is a comparison diagram of the fingerprint image sensed by the image sensor of Fig. 1 and the area comparison of P-polarized light and S-polarized light received by the image sensor;
  • 4B is a fingerprint image of a fake finger sensed by the image sensor of FIG. 1;
  • 5A is an average grayscale distribution diagram of a fingerprint image of a real finger sensed by the image sensor of FIG. 1 on a diagonal line M-N;
  • FIG. 5B is an average grayscale distribution diagram of the fingerprint image of the fake finger sensed by the image sensor of FIG. 1 on the diagonal line M-N;
  • Fig. 6 is a schematic diagram of the controller in Fig. 1 processing a fingerprint image
  • Fig. 7 is another schematic diagram of the controller in Fig. 1 processing a fingerprint image
  • FIG. 8 is a schematic diagram of the controller in FIG. 1 processing the first characteristic value and the second characteristic value of the fingerprint image.
  • FIG. 1 is a schematic cross-sectional view of an electronic device according to an embodiment of the invention.
  • the electronic device 100 of this embodiment includes a display 105 and an under-screen fingerprint sensing device 200.
  • the electronic device 100 is, for example, a smart phone, a tablet computer, a notebook computer, a personal digital assistant (PDA) or other appropriate electronic devices.
  • the under-screen fingerprint sensor 200 is used to match the display 105, and includes an image sensor 210 and a controller 230.
  • the image sensor 210 is disposed under the display 105.
  • the display 105 emits the illuminating light 60, the illuminating light 60 is transmitted to the finger 50 pressed on the display 105, and the finger 50 reflects the illuminating light 60 into a signal light 70 that carries fingerprint information of the finger.
  • the signal light 70 penetrates the display 105 to form a fingerprint image on the image sensor 210. In this way, the image sensor 210 can sense the fingerprint image of the finger 50.
  • the controller 230 is electrically connected to the image sensor 210 and is used to process the fingerprint image sensed by the image sensor 210.
  • the display 105 includes a cover glass 120, a linear polarizer 116, a phase retarder film 114, and an organic light emitting diode display panel 112.
  • the linear polarizer 116 is disposed between the glass cover 120 and the image sensor 210.
  • the phase retardation film 114 is disposed between the linear polarizer 116 and the image sensor 210.
  • the phase retardation film 114 is, for example, a wave plate, which may be formed of the material of the display itself, or an additional wave plate.
  • the organic light emitting diode display panel 112 is disposed between the phase retardation film 114 and the image sensor 210.
  • a liquid crystal display panel, a micro-light-emitting diode display panel, an electrophoretic display panel, or other suitable display panels can also be used to replace the organic light-emitting diode display panel 112.
  • the under-screen fingerprint sensing device 200 further includes a lens 220, which is arranged on the path of the signal light 70 and located between the display 105 and the image sensor 210.
  • the lens 220 may include one or more lenses, which can image the signal light 70 on the image sensor 210 to form a fingerprint image on the image sensor 210.
  • the illuminating light 60 emitted by the organic light emitting diode display panel 112 does not have polarization, and after it penetrates the phase retardation film 114, it still does not have polarization.
  • the illumination light 60 penetrates the linear polarizer 116, it will have a polarization direction K0, where the polarization direction K0 can be decomposed into two components, a first polarization direction K1 and a second polarization direction K2, as shown in FIGS. 2A and 2B
  • the first polarization direction K1 is the P polarization direction
  • the second polarization direction K2 is the S polarization direction.
  • the illumination light 60 having the polarization direction K0 can be regarded as a combination of the illumination light 62 having the first polarization direction K1 and the illumination light 64 having the second polarization direction K2.
  • FIG. 2A shows a situation in which the illumination light having the P polarization direction in FIG. 1 is reflected by a finger
  • FIG. 2B shows a situation in which the illumination light having an S polarization direction in FIG. 1 is reflected by the finger.
  • the illumination light 62 with the first polarization direction K1 travels in the glass cover 120 (as shown in FIG. 2A), and is partially reflected by the finger 50 at the upper surface 122 of the glass cover 120 as a signal Light 72, and another part of the illuminating light 82 is transmitted in the finger 50.
  • the illuminating light 64 with the second polarization direction K2 travels in the glass cover 120 (as shown in FIG.
  • the signal light 72 and the signal light 74 synthesize the signal light 70 and transmit to the direction of the image sensor 210.
  • Fig. 3 is a distribution curve of the reflectivity and transmittance of the illuminating light at the interface between the finger and the glass cover of Fig.
  • the image sensor 210 receives the signal light 70 reflected by the illumination light 60 with a larger incident angle at the outer ring, the signal light 72 (P polarized light) and the signal light 74 ( S-polarized light) has a greater difference in light intensity.
  • FIG. 4A is a comparison diagram of the fingerprint image sensed by the image sensor of FIG. 1 and the area comparison of the P-polarized light and S-polarized light it receives.
  • the image brightness of the area where S+P is located is mainly contributed by the signal light 72 (P-polarized light) and the signal light 74 (S-polarized light).
  • DC value direct current value of the fingerprint image
  • FIG. 4B is a fingerprint image of a fake finger sensed by the image sensor of FIG. 1.
  • FIG. 5A is an average gray scale distribution diagram on the diagonal MN of the fingerprint image of the real finger sensed by the image sensor of FIG. 1
  • FIG. 5B is the fingerprint image of the fake finger sensed by the image sensor of FIG.
  • the average gray scale distribution on the corner line MN The average gray scale of a certain pixel on the diagonal line M-N in FIGS. 5A and 5B is obtained by averaging the gray scale values of several pixels near the pixel and the gray scale value of the pixel itself. Comparing FIGS. 4A and 4B, and FIGS.
  • Fig. 6 is a schematic diagram of the controller in Fig. 1 processing a fingerprint image.
  • the controller 230 is used to make an inner product of the grayscale values and the Haar characteristics on the two axes L1 and L2 of the fingerprint image in different directions, so as to Get the first result.
  • the controller first performs blurring processing on the fingerprint image, and then performs grayscale values and Haar characteristics on the two axes L1 and L2 of the blurred fingerprint image in different directions.
  • Inner product here is, for example, mean blur or Gaussian blur.
  • the grayscale value of each pixel and the grayscale values of several pixels around the pixel are averaged, and Use this average value as the new grayscale value of this pixel.
  • the Haar feature is that the middle area C1 has a first value and the side areas C2 and C3 have a function of a second value, wherein the first value is greater than the second value.
  • the first value is +1
  • the second value is -1.
  • the blurred fingerprint image has, for example, 200 ⁇ 200 pixels, and the first to 75th pixels from the left end of the Haar feature each have a value of, for example, -1, and the 76th to 125th pixels each have The value of is set to, for example, +1, and the value of each of the 126th to 200th pixels is set to, for example, -1.
  • the blurred fingerprint image also has 200 pixels on the axis L1, and each pixel has its own grayscale value, and the grayscale value represents the brightness of the blurred fingerprint image. Then, the grayscale values of the 200 pixels on the axis L1 are sequentially and respectively multiplied by the value of the 200 pixels of the Haar feature (that is, -1 or +1) to obtain 200 products, and then Add these 200 products together to obtain the value obtained after the inner product operation described above.
  • the controller 230 adds the two inner product values respectively corresponding to the axis L1 and the axis L2 to obtain the first characteristic value.
  • the inner product value or the first characteristic value of the real finger in Fig. 5A is smaller after the gray scale values on the axes L1 and L2 are calculated with the Haar feature.
  • the 5B fake finger has a larger inner product value or first feature value, so the calculated first feature value can be used to distinguish whether the sensed finger is a real finger or a fake finger.
  • Fig. 7 is another schematic diagram of the controller in Fig. 1 processing a fingerprint image. 1 and 7, the controller 230 is used to calculate the average gray scale of the central area D2 of the fingerprint image and the respective gray scale averages of the two peripheral areas D1 and D3 on both sides of the central area D2 to obtain the first Two results. In addition, the controller 230 is used to synthesize the first result and the second result to determine whether the fingerprint image is from a real finger or a fake finger.
  • the average gray level of the central area D2 is R2, and the average gray levels of the two peripheral areas D1 and D3 are R1 and R3, respectively.
  • the controller 230 is used to perform arithmetic operations on R1, R2, and R3 to obtain the first Two eigenvalues.
  • the central area D2 and the two peripheral areas D1 and D3 are arranged on the diagonal of the fingerprint image, and the direction of the diagonal can be determined according to the direction of the penetration axis of the linear polarizer 116. That is, the direction with the greater difference between the second feature value of the real finger and the fake finger is selected as the direction of the diagonal.
  • the above-mentioned arithmetic operation is, for example, (R2-R1)+(R2-R3), or the above-mentioned arithmetic operation is, for example, R2-R1-R3. Comparing FIG. 5A, FIG. 5B, and FIG.
  • the second feature value obtained by these two arithmetic operations is that the second feature value of the real finger is smaller, while the second feature value of the fake finger is larger, so the calculated second feature value can be used to distinguish What is sensed is a real finger or a fake finger.
  • FIG. 8 is a schematic diagram of the controller in FIG. 1 processing the first characteristic value and the second characteristic value of the fingerprint image. 1 and 8, the controller 230 is used to determine whether the two-dimensional coordinates (such as the coordinates in the coordinate plane of FIG. 8) formed by the first characteristic value and the second characteristic value fall within the predetermined area F1 or F2 (For example, whether it falls within the elliptical area of the predetermined area F1, or whether it falls within the ellipse area of the predetermined area F2), and the selection of the predetermined area F1, the predetermined area F2, or other areas can be based on the test of the real finger and the fake finger. Case to decide.
  • the two-dimensional coordinates such as the coordinates in the coordinate plane of FIG. 8
  • the controller 230 determines that the fingerprint image is from a real finger. If the two-dimensional coordinates fall outside the predetermined area F1 or F2, the controller 230 determines that the fingerprint image is from a fake finger. In this way, the under-screen fingerprint sensing device 100 of this embodiment can achieve an anti-spoofing effect in fingerprint sensing, thereby enhancing the security of the user's personal data.
  • the real finger and the fake finger are judged based on the result of combining the first feature value and the second feature value.
  • the real finger and the fake finger can also be judged based on the first feature value alone, or the real finger and the fake finger can be judged based on the second feature value alone.
  • the controller 230 may only calculate the first characteristic value, and determine whether the first characteristic value falls within a preset range. If the first feature value falls within the preset range, it is determined that the fingerprint image is from a real finger; if the first feature value falls outside the preset range, it is determined that the fingerprint image is from a fake finger.
  • the controller 230 may only calculate the second characteristic value and determine whether the second characteristic value falls within a preset range. If the second feature value falls within the preset range, it is determined that the fingerprint image is from a real finger; if the second feature value falls outside the preset range, it is determined that the fingerprint image is from a fake finger.
  • the controller 230 is, for example, a central processing unit (CPU), a microprocessor (microprocessor), a digital signal processor (digital signal processor, DSP), a programmable controller, and a programmable controller.
  • CPU central processing unit
  • microprocessor microprocessor
  • DSP digital signal processor
  • programmable controller programmable controller
  • programmable controller programmable controller
  • programmable controller programmable controller
  • programmable controller programmable controller
  • a logic device programmable logic device, PLD
  • the functions of the controller 230 may be implemented as multiple program codes. These program codes are stored in a memory, and the controller 230 executes the program codes.
  • each function of the controller 230 may be implemented as one or more circuits. The present invention does not limit the use of software or hardware to implement the functions of the controller 230.
  • the controller performs the inner product of the grayscale value and the Haar feature on the two axes of the fingerprint image in different directions, and/or calculates The average gray scale of the central area of the fingerprint image and the respective gray scale averages of the two peripheral areas on both sides of the central area are used to determine whether the fingerprint image comes from a real finger or a fake finger. Therefore, the under-screen fingerprint sensing device of the embodiment of the present invention can achieve an anti-spoofing effect in fingerprint sensing, thereby improving the security of the user's personal data.

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Abstract

本发明提供一种屏下式指纹感测装置,包括图像传感器及控制器。图像传感器配置于显示器下方,其中显示器发出照明光,照明光传递至按压于显示器上的手指,手指将照明光反射成携带手指的指纹信息的信号光,信号光穿透显示器而在图像传感器上形成指纹图像。控制器电性连接至图像传感器,且用以处理图像传感器所感测到的指纹图像。控制器用以对指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,并借此判断指纹图像是来自真手指或假手指。

Description

屏下式指纹感测装置 技术领域
本发明涉及一种感测装置,尤其涉及一种屏下式指纹感测装置。
背景技术
随着可携式电子装置朝向大屏占比发展,原本置于电子装置正面的电容式指纹传感器便不再适用,而需改成置于电子装置的侧面或背面。然而,置于侧面或背面的指纹传感器在使用上有不便利之处,因此屏下式指纹传感器便被发展出来。
屏下式指纹传感器大致上可分为光学式指纹传感器与超声波式指纹传感器,其中又以光学式指纹传感器成本较低且较适合量产。由于指纹感测攸关使用者的个人数据的安全性,因此,尚需发展出反欺骗(anti-spoofing)的功能。例如,欲窃取个人数据的人可能可以在环境中采集使用者的指纹,并制作成具有此指纹的假手指,再用假手指按压电子装置以达成指纹成功识别而解锁。因此,需发展出能够识别出假手指而非真手指的指纹传感器,以进一步提升使用者的个人数据的安全性。
发明内容
本发明是针对一种屏下式指纹感测装置,其可识别出真手指与假手指。
本发明的一实施例提出一种屏下式指纹感测装置,用以与显示器搭配,显示器发出照明光,照明光传递至按压于显示器上的手指,手指将照明光反射成携带手指的指纹信息的信号光。屏下式指纹感测装置包括图像传感器及控制器。图像传感器配置于显示器下方,其中信号光穿透显示器而在图像传感器上形成指纹图像。控制器电性连接至图像传感器,处理图像传感器所感测到的指纹图像,对指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征(Haar-like feature)作内积,并借此判断指纹图像是来自真手指或假手指。
本发明的一实施例提出一种屏下式指纹感测装置,用以与显示器搭配,显示器发出照明光,照明光传递至按压于显示器上的手指,手指将照明光反 射成携带手指的指纹信息的信号光。屏下式指纹感测装置包括图像传感器及控制器。图像传感器配置于显示器下方,其中信号光穿透显示器而在图像传感器上形成指纹图像。控制器电性连接至图像传感器,且用以处理图像传感器所感测到的指纹图像。控制器用以计算指纹图像的中心区域的灰阶平均值及在中心区域两侧的二周边区域的各自的灰阶平均值,并借此判断指纹图像是来自真手指或假手指。
本发明的一实施例提出一种屏下式指纹感测装置,用以与显示器搭配,显示器发出照明光,照明光传递至按压于显示器上的手指,手指将照明光反射成携带手指的指纹信息的信号光。屏下式指纹感测装置包括图像传感器及控制器。图像传感器配置于显示器下方,其中信号光穿透显示器而在图像传感器上形成指纹图像。控制器电性连接至图像传感器,且用以处理图像传感器所感测到的指纹图像。控制器用以对指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,以获得第一结果。控制器用以计算指纹图像的中心区域的灰阶平均值及在中心区域两侧的二周边区域的各自的灰阶平均值,以获得第二结果。控制器用以综合第一结果与第二结果来判断指纹图像是来自真手指或假手指。
在本发明的实施例的屏下式指纹感测装置中,控制器对指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,和/或计算指纹图像的中心区域的灰阶平均值及在中心区域两侧的二个周边区域的各自的灰阶平均值,并借此判断指纹图像是来自真手指或假手指。因此,本发明的实施例的屏下式指纹感测装置在指纹感测上可以达到防欺骗的效果,进而提升使用者的个人数据的安全性。
附图说明
图1为本发明的一实施例的电子装置的剖面示意图;
图2A示出图1中具有P偏振方向的照明光被手指反射的情形;
图2B示出图1中具有S偏振方向的照明光被手指反射的情形;
图3为图1的手指与玻璃盖的界面对照明光的反射率及穿透率相对于入射此界面的入射角的分布曲线;
图4A为图1的图像传感器所感测到的指纹图像与其所接收到的P偏振 光与S偏振光的区域对照图;
图4B为图1的图像传感器感测到假手指的指纹图像;
图5A为图1的图像传感器所感测到的真手指的指纹图像于对角线M-N上的平均灰阶分布图;
图5B为图1的图像传感器所感测到的假手指的指纹图像于对角线M-N上的平均灰阶分布图;
图6为图1中的控制器处理指纹图像的示意图;
图7为图1中的控制器处理指纹图像的另一示意图;
图8为图1中的控制器处理指纹图像的第一特征值与第二特征值的示意图。
具体实施方式
现将详细地参考本发明的示范性实施例,示范性实施例的实例说明于附图中。只要有可能,相同元件符号在附图和描述中用来表示相同或相似部分。
图1为本发明的一实施例的电子装置的剖面示意图。请参照图1,本实施例的电子装置100包括显示器105及屏下式指纹感测装置200。电子装置100例如为智能手机、平板计算机、笔记本电脑、个人数字助理(personal digital assistant,PDA)或其他适当的电子装置。屏下式指纹感测装置200用以与显示器105搭配,且包括图像传感器210及控制器230。图像传感器210配置于显示器105下方。显示器105发出照明光60,照明光60传递至按压于显示器105上的手指50,手指50将照明光60反射成携带手指的指纹信息的信号光70。信号光70穿透显示器105而在图像传感器210上形成指纹图像。如此一来,图像传感器210便能够感测到手指50的指纹图像。控制器230电性连接至图像传感器210,且用以处理图像传感器210所感测到的指纹图像。
在本实施例中,显示器105包括玻璃盖(cover glass)120、线偏振片116、相位延迟膜(phase retarder film)114及有机发光二极管显示面板112。手指按压于玻璃盖120上。线偏振片116配置于玻璃盖120与图像传感器210之间。相位延迟膜114配置于线偏振片116与图像传感器210之间,其中相位延迟膜114例如为波片(wave plate),其可以是显示器本身的材料所形成,或是额外加入的波片所形成。有机发光二极管显示面板112配置于相位延迟膜114与图像传感器210之间。在其他实施例中,亦可以用液晶显示面板、 微发光二极管显示面板、电泳显示面板或其他适当的显示面板来取代有机发光二极管显示面板112。
在本实施例中,屏下式指纹感测装置200还包括镜头220,配置于信号光70的路径上,且位于显示器105与图像传感器210之间。镜头220可包括一或多片透镜,其可将信号光70成像于图像传感器210上,以在图像传感器210上形成指纹图像。
具体而言,有机发光二极管显示面板112发出的照明光60是不具有偏振性的,且当其穿透相位延迟膜114后,仍不具有偏振性。然而,当照明光60穿透线偏振片116后,会具有偏振方向K0,其中偏振方向K0可被分解成第一偏振方向K1与第二偏振方向K2两个分量,如图2A及图2B所示,第一偏振方向K1为P偏振方向,而第二偏振方向K2为S偏振方向。换句话说,具有偏振方向K0的照明光60可视为具有第一偏振方向K1的照明光62与具有第二偏振方向K2的照明光64所合成。
图2A示出图1中具有P偏振方向的照明光被手指反射的情形,而图2B示出图1中具有S偏振方向的照明光被手指反射的情形。请参照图1、图2A及图2B,具有第一偏振方向K1的照明光62在玻璃盖120中行进(如图2A),并在玻璃盖120的上表面122处被手指50部分反射成信号光72,而另一部分的照明光82则在手指50中传递。另一方面,具有第二偏振方向K2的照明光64在玻璃盖120中行进(如图2B),并在玻璃盖120的上表面122处被手指50部分反射成信号光74,而另一部分的照明光84则在手指50中传递。其中,信号光72与信号光74合成信号光70,而往图像传感器210的方向传递。
图像传感器210所感测到的信号光72与信号光74的光强度及其比例是有关于手指50与玻璃盖120的折射率所造成的反射率。图3为图1的手指与玻璃盖的界面对照明光的反射率及穿透率相对于入射此界面的入射角的分布曲线,其中,R p为此界面对照明光62的反射率相对于入射角的分布曲线,R s为此界面对照明光64的反射率相对于入射角的分布曲线,T p为此界面对照明光62的穿透率相对于入射角的分布曲线,而T s为此界面对照明光64的穿透率相对于入射角的分布曲线。其中,T p=1-R p,且T s=1-R s。由图3可知,在入射角较大处所对应的信号光72(P偏振光)与信号光74(S偏振光)的 光强度差异越大。由于图像传感器210在越外圈处是收到越大入射角的照明光60所反射成的信号光70,因此越外圈处所感测到的信号光72(P偏振光)与信号光74(S偏振光)的光强度差异越大。
图4A为图1的图像传感器所感测到的指纹图像与其所接收到的P偏振光与S偏振光的区域对照图。请参照图1、图2A、图2B及图4A,图4A中,P所在区域的图像亮度主要是由信号光72(P偏振光)所贡献,S所在区域的图像亮度主要是由信号光74(S偏振光)所贡献,而S+P所在区域的图像亮度主要是由信号光72(P偏振光)与信号光74(S偏振光)两者所共同贡献。P所在区域因为穿透光多,所以指纹图像的对比度较强;S所在区域因为穿透光少,所以指纹图像的对比度较弱;P所在区域因为反射光少,所以指纹图像的直流值(DC value)低,也就是平均亮度较低;S所在区域因为反射光多,所以指纹图像的直流值高,也就是平均亮度较高。
图4B为图1的图像传感器感测到假手指的指纹图像。图5A为图1的图像传感器所感测到的真手指的指纹图像于对角线M-N上的平均灰阶分布图,而图5B为图1的图像传感器所感测到的假手指的指纹图像于对角线M-N上的平均灰阶分布图。在图5A与图5B的对角线M-N上的某个像素的平均灰阶是借由将此像素附近的几个像素的灰阶值与此像素本身的灰阶值取平均值而得。比较图4A与图4B,以及图5A与图5B,可发现真手指的指纹图像于中央的平均亮度较低,而对角线M-N上靠近两端的平均亮度较高。相反地,假手指的指纹图像于中央的平均亮度较高,而对角线M-N上靠近两端的平均亮度较低。会造成此种现象的主要原因之一是假手指的折射率与真手指有差异,因此会造成P偏振光与S偏振光的反射率不同,进而造成平均亮度在不同位置的分布曲线的不同。因此,本发明的实施例便可对此现象加以利用,以产生识别真手指与假手指的方案,这将于以下内容中详述。
图6为图1中的控制器处理指纹图像的示意图。请参照图1与图6,在本实施例中,控制器230用以对指纹图像的两个方向不同的轴线L1与L2上的灰阶值与哈尔特征作内积(inner product),以获得第一结果。具体而言,在本实施例中,控制器先对指纹图像作模糊化处理后,再对经模糊化的指纹图像的两个方向不同的轴线L1与L2上的灰阶值与哈尔特征作内积。此处的模糊化例如是平均模糊化(mean blur)或高斯模糊化(Gaussian blur),例如 将每个像素的灰阶值与此像素的周围的几个像素的灰阶值取平均值,并以此平均值作为此像素的新灰阶值。
在本实施例中,哈尔特征为中间区域C1具有第一数值而两侧区域C2与C3具有第二数值的函数,其中第一数值大于第二数值。举例而言,第一数值为+1,而第二数值为-1。经模糊化后的指纹图像例如具有200×200个像素,而哈尔特征从左端数来的第1到75个像素所各自具有的数值例如设为-1,第76至125个像素所各自具有的数值例如设为+1,而第126至第200个像素所各自具有的数值例如设为-1。经模糊化后的指纹图像的轴线L1上亦具有200个像素,而每个像素具有各自的灰阶值,而此灰阶值代表经模糊化后的指纹图像的亮度。接着,将轴线L1上的这200个像素所具有的灰阶值依序分别地与哈尔特征的这200个像素的数值(即-1或+1)相乘,以得到200个积,而后再将这200个积相加,即可获得上述经内积运算后所得到的数值。
然后,控制器230将分别对应于轴线L1与轴线L2的两个内积值相加,以获得第一特征值。比较图5A、图5B与图6可知,轴线L1与L2上的灰阶值经由与哈尔特征作内积运算后,图5A的真手指的内积值或第一特征值越小,而图5B的假手指的内积值或第一特征值越大,因此所运算出的第一特征值可用以分辨所感测的是真手指或假手指。
图7为图1中的控制器处理指纹图像的另一示意图。请参照图1与图7,控制器230用以计算指纹图像的中心区域D2的灰阶平均值及在中心区域D2两侧的二周边区域D1与D3的各自的灰阶平均值,以获得第二结果。此外,控制器230用以综合第一结果与第二结果来判断指纹图像是来自真手指或假手指。
具体而言,中心区域D2的灰阶平均值为R2,二周边区域D1与D3的灰阶平均值分别为R1与R3,控制器230用以对R1、R2、R3作算术运算,以获得第二特征值。在本实施例中,中心区域D2与该二周边区域D1与D3排列于指纹图像的对角线上,而此对角线的方向可依据线偏振片116的穿透轴方向来作决定,也就是选择真手指与假手指的第二特征值的区别较大的方向作为此对角线的方向。在一实施例中,上述的算术运算例如为(R2-R1)+(R2-R3),或者上述的算术运算例如为R2-R1-R3,在比较图5A、图5B及图7可知,对于这两种算术运算所获得的第二特征值而言,都是真手指 的第二特征值较小,而假手指的第二特征值较大,因此所运算出的第二特征值可用以分辨所感测的是真手指或假手指。
图8为图1中的控制器处理指纹图像的第一特征值与第二特征值的示意图。请参照图1与图8,控制器230用以判断第一特征值与第二特征值所形成的二维坐标(如在图8的坐标平面中的坐标)是否落在预定区域F1或F2内(例如是否落在预定区域F1的椭圆区域内,或是否落在预定区域F2的椭圆区域内),而预定区域F1、预定区域F2或其他区域的选择可根据所实验的真手指与假手指的案例来决定。若二维坐标落在预定区域F1或F2内,则控制器230判断指纹图像是来自真手指。若二维坐标落在预定区域F1或F2外,则控制器230判断指纹图像是来自假手指。如此一来,本实施例的屏下式指纹感测装置100在指纹感测上便可以达到防欺骗的效果,进而提升使用者的个人数据的安全性。
上述实施例是以综合第一特征值与第二特征值的结果来判断出真手指与假手指。然而,在其他实施例中,也可以单就第一特征值来判断出真手指与假手指,或者是单就第二特征值来判断出真手指与假手指。举例而言,控制器230可以只计算出第一特征值,并判断第一特征值是否落在预设范围内。若第一特征值落在预设范围内,则判断指纹图像是来自真手指;若第一特征值落在预设范围外,则判断指纹图像是来自假手指。或者,控制器230可以只计算出第二特征值,并判断第二特征值是否落在预设范围内。若第二特征值落在预设范围内,则判断指纹图像是来自真手指;若第二特征值落在预设范围外,则判断指纹图像是来自假手指。
在一实施例中,控制器230例如为中央处理单元(central processing unit,CPU)、微处理器(microprocessor)、数字信号处理器(digital signal processor,DSP)、可程序化控制器、可程序化逻辑设备(programmable logic device,PLD)或其他类似装置或这些装置的组合,本发明并不加以限制。此外,在一实施例中,控制器230的各功能可被实作为多个程序代码。这些程序代码会被储存在一个内存中,由控制器230来执行这些程序代码。或者,在一实施例中,控制器230的各功能可被实作为一或多个电路。本发明并不限制用软件或硬件的方式来实作控制器230的各功能。
综上所述,在本发明的实施例的屏下式指纹感测装置中,控制器对指纹 图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,和/或计算指纹图像的中心区域的灰阶平均值及在中心区域两侧的二个周边区域的各自的灰阶平均值,并借此判断指纹图像是来自真手指或假手指。因此,本发明的实施例的屏下式指纹感测装置在指纹感测上可以达到防欺骗的效果,进而提升使用者的个人数据的安全性。
最后应说明的是:以上各实施例仅用以说明本发明的技术方案,而非对其限制;尽管参照前述各实施例对本发明进行了详细的说明,本领域的普通技术人员应当理解:其依然可以对前述各实施例所记载的技术方案进行修改,或者对其中部分或者全部技术特征进行等同替换;而这些修改或者替换,并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (20)

  1. 一种屏下式指纹感测装置,其特征在于,用以与显示器搭配,所述显示器发出照明光,所述照明光传递至按压于所述显示器上的手指,所述手指将所述照明光反射成携带所述手指的指纹信息的信号光,所述屏下式指纹感测装置包括:
    图像传感器,配置于所述显示器下方,其中所述信号光穿透所述显示器而在所述图像传感器上形成指纹图像;以及
    控制器,电性连接至所述图像传感器,处理所述图像传感器所感测到的指纹图像,对所述指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,并借此判断所述指纹图像是来自真手指或假手指。
  2. 根据权利要求1所述的屏下式指纹感测装置,其特征在于,所述控制器先对所述指纹图像作模糊化处理后,再对经模糊化的所述指纹图像的两个方向不同的轴线上的灰阶值与所述哈尔特征作内积。
  3. 根据权利要求2所述的屏下式指纹感测装置,其特征在于,所述控制器将对应于两个方向不同的轴线的两个内积值相加,并判断相加后的数值是否落在预设范围内,所述控制器反应于所述相加后的数值是落在所述预设范围内而判断所述指纹图像是来自真手指,且所述控制器反应于所述相加后的数值是落在所述预设范围外而判断所述指纹图像是来自假手指。
  4. 根据权利要求1所述的屏下式指纹感测装置,其特征在于,所述哈尔特征为中间区域具有第一数值而两侧区域具有第二数值的函数,其中所述第一数值大于所述第二数值。
  5. 根据权利要求1所述的屏下式指纹感测装置,其特征在于,所述显示器包括:
    玻璃盖,其中所述手指按压于所述玻璃盖上;
    线偏振片,配置于所述玻璃盖与所述图像传感器之间;
    相位延迟膜,配置于所述线偏振片与所述图像传感器之间;以及
    有机发光二极管显示面板,配置于所述相位延迟膜与所述图像传感器之间。
  6. 根据权利要求1所述的屏下式指纹感测装置,其特征在于,还包括镜头,配置于所述信号光的路径上,且位于所述显示器与所述图像传感器之间。
  7. 一种屏下式指纹感测装置,其特征在于,用以与显示器搭配,所述显示器发出照明光,所述照明光传递至按压于所述显示器上的手指,所述手指将所述照明光反射成携带所述手指的指纹信息的信号光,所述屏下式指纹感测装置包括:
    图像传感器,配置于所述显示器下方,其中所述信号光穿透所述显示器而在所述图像传感器上形成指纹图像;以及
    控制器,电性连接至所述图像传感器,处理所述图像传感器所感测到的指纹图像,计算所述指纹图像的中心区域的灰阶平均值及在所述中心区域两侧的二周边区域的各自的灰阶平均值,并借此判断所述指纹图像是来自真手指或假手指。
  8. 根据权利要求7所述的屏下式指纹感测装置,其特征在于,所述中心区域与所述二周边区域排列于所述指纹图像的对角线上。
  9. 根据权利要求7所述的屏下式指纹感测装置,其特征在于,所述中心区域的灰阶平均值为R2,所述二周边区域的灰阶平均值分别为R1与R3,所述控制器用以对R1、R2、R3作算术运算,以获得特征值,并判断所述特征值是否落在预设范围内,所述控制器反应于所述特征值是落在所述预设范围内而判断所述指纹图像是来自真手指,且所述控制器反应于所述特征值是落在所述预设范围外而判断所述指纹图像是来自假手指。
  10. 根据权利要求9所述的屏下式指纹感测装置,其特征在于,所述算术运算为(R2-R1)+(R2-R3),或者所述算术运算为R2-R1-R3。
  11. 根据权利要求7所述的屏下式指纹感测装置,其特征在于,所述显示器包括:
    玻璃盖,其中所述手指按压于所述玻璃盖上;
    线偏振片,配置于所述玻璃盖与所述图像传感器之间;
    相位延迟膜,配置于所述线偏振片与所述图像传感器之间;以及
    有机发光二极管显示面板,配置于所述相位延迟膜与所述图像传感器之间。
  12. 根据权利要求7所述的屏下式指纹感测装置,其特征在于,还包括镜头,配置于所述信号光的路径上,且位于所述显示器与所述图像传感器之间。
  13. 一种屏下式指纹感测装置,其特征在于,用以与显示器搭配,所述显示器发出照明光,所述照明光传递至按压于所述显示器上的手指,所述手指将所述照明光反射成携带所述手指的指纹信息的信号光,所述屏下式指纹感测装置包括:
    图像传感器,配置于所述显示器下方,其中所述信号光穿透所述显示器而在所述图像传感器上形成指纹图像;以及
    控制器,电性连接至所述图像传感器,处理所述图像传感器所感测到的指纹图像,对所述指纹图像的两个方向不同的轴线上的灰阶值与哈尔特征作内积,以获得第一结果,所述控制器用以计算所述指纹图像的中心区域的灰阶平均值及在所述中心区域两侧的二周边区域的各自的灰阶平均值,以获得第二结果,且所述控制器用以综合所述第一结果与所述第二结果来判断所述指纹图像是来自真手指或假手指。
  14. 根据权利要求13所述的屏下式指纹感测装置,其特征在于,所述控制器用以先对所述指纹图像作模糊化处理后,再对经模糊化的所述指纹图像的两个方向不同的轴线上的灰阶值与所述哈尔特征作内积。
  15. 根据权利要求14所述的屏下式指纹感测装置,其特征在于,所述控制器将对应于两个方向不同的轴线的两个内积值相加,以获得第一特征值,所述中心区域的灰阶平均值为R2,所述二周边区域的灰阶平均值分别为R1与R3,所述控制器用以对R1、R2、R3作算术运算,以获得第二特征值,所述控制器用以判断所述第一特征值与所述第二特征值所形成的二维坐标是否落在预定区域内,所述控制器反应于所述二维坐标是落在所述预定区域内而判断所述指纹图像是来自真手指,且所述控制器反应于所述二维坐标是落在所述预定区域外而判断所述指纹图像是来自假手指。
  16. 根据权利要求15所述的屏下式指纹感测装置,其特征在于,所述哈尔特征为中间区域具有第一数值而两侧区域具有第二数值的函数,其中所述第一数值大于所述第二数值。
  17. 根据权利要求15所述的屏下式指纹感测装置,其特征在于,所述算术运算为(R2-R1)+(R2-R3),或者所述算术运算为R2-R1-R3。
  18. 根据权利要求13所述的屏下式指纹感测装置,其特征在于,所述中心区域与所述二周边区域排列于所述指纹图像的对角线上。
  19. 根据权利要求13所述的屏下式指纹感测装置,其特征在于,所述显示器包括:
    玻璃盖,其中所述手指按压于所述玻璃盖上;
    线偏振片,配置于所述玻璃盖与所述图像传感器之间;
    相位延迟膜,配置于所述线偏振片与所述图像传感器之间;以及
    有机发光二极管显示面板,配置于所述相位延迟膜与所述图像传感器之间。
  20. 根据权利要求13所述的屏下式指纹感测装置,其特征在于,还包括镜头,配置于所述信号光的路径上,且位于所述显示器与所述图像传感器之间。
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