WO2001084477A1 - Method and apparatus for discriminating latent fingerprint in optical fingerprint input apparatus - Google Patents

Method and apparatus for discriminating latent fingerprint in optical fingerprint input apparatus Download PDF

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Publication number
WO2001084477A1
WO2001084477A1 PCT/KR2001/000708 KR0100708W WO0184477A1 WO 2001084477 A1 WO2001084477 A1 WO 2001084477A1 KR 0100708 W KR0100708 W KR 0100708W WO 0184477 A1 WO0184477 A1 WO 0184477A1
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WO
WIPO (PCT)
Prior art keywords
fingerprint
image
discriminating
detected
backlight
Prior art date
Application number
PCT/KR2001/000708
Other languages
French (fr)
Inventor
Dong-Won Lee
Byung-Jin Lee
Soon-Won Jung
Hwi-Seok Lee
Jae-Hyun Jun
Original Assignee
Nitgen Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nitgen Co., Ltd. filed Critical Nitgen Co., Ltd.
Priority to JP2001581216A priority Critical patent/JP4520685B2/en
Priority to AU55085/01A priority patent/AU5508501A/en
Priority to US10/258,455 priority patent/US6885017B2/en
Publication of WO2001084477A1 publication Critical patent/WO2001084477A1/en
Priority to US11/067,792 priority patent/US6989547B2/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
    • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
    • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
    • G06V40/12—Fingerprints or palmprints
    • G06V40/13—Sensors therefor
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F18/00—Pattern recognition

Definitions

  • This invention relates to a method and an apparatus for discriminating a latent fingerprint that can prevent a fingerprint recognition device from mis-recognizing a latent fingerprint as a fingerprint of a biomass due to a fingerprint residual on an imaging surface of an optical fingerprint input apparatus.
  • a fingerprint recognition device can be utilized in a wide scale as a device for comparing and recognizing fingerprints between an inputted fingerprint and a pre- registered fingerprint of a user in the form of a locking device at a door or a safe, access control to a gate, attendance control of employees, access control to a computer, etc.
  • the fingerprint input apparatuses for receiving fingerprints to perform such fingerprint recognition are mainly classified into two types: an optical type and a non-optical type.
  • the fingerprint recognition device employing an optical fingerprint input apparatus is a device that illuminates a light to a fingerprint laid on a prism, interprets a fingerprint image reflected according to the shapes of valleys or ridges of the fingerprint and formed on an image sensor, and compares the interpreted image with a pre-stored fingerprint.
  • the optical fingerprint input apparatuses are mainly classified into an absorption type and a scattering type.
  • Fig. 1 is a schematic diagram illustrating an operational principle of a fingerprint input apparatus of an absorption type, which comprises a backlight 112, a triangular prism 110, a lens 114, an image sensor 116, and an image processor 125.
  • the backlight 112 uses a plurality of LED aligned.
  • the triangular prism 110 is a prism of a right triangular shape that generates a total reflection inside of an imaging surface when no fingerprint is inputted.
  • the image sensor 116 is an element outputting electric signals corresponding to an amount of inputted light, such as a CCD or a CMOS sensor, well known to those skilled in the art.
  • the inclined surface of the triangular prism 110 is an imaging surface, while an internal plane of the imaging surface 118 is a total reflection surface causing the total reflection.
  • the light originating from the backlight 112 is totally reflected from inside of the imaging surface of the triangular prism 110, and is incident on the image sensor 116 through the lens 1 14.
  • the light illuminated onto the valleys of the fingerprint is totally reflected from the internal surface of the imaging surface 118 and reaches the image sensor 116 because the valleys of the fingerprint are not in contact with the imaging surface.
  • the light illuminated onto the ridges of the fingerprint is not totally reflected from the internal surface of the imaging surface 118 but only a part thereof reaches the image sensor 116.
  • the image sensor 116 Accordingly, the amounts of light incident on the image sensor 116 differ between the valleys and the ridges, and as a consequence, the image sensor 116 outputs electric signals of different levels depending on a pattern of a fingerprint.
  • the image processor 125 formulates the output values of the image sensor 116 into digital signals so as to recognize a fingerprint pattern.
  • Figs. 2A and 2B are schematic diagrams illustrating an operational principle of a fingerprint input apparatus of a scattering type.
  • the fingerprint input apparatus in Fig. 2 A comprises a backlight 212, a prism 210, a lens 214, and a image sensor 216 to have a similar construction to the one in Fig. 1.
  • the prism 210 is of a ladder shape rather than a triangular shape.
  • the light is incident on the imaging surface 218 of the prism 210 from the backlight 211 at an angle far smaller than the right angle or a critical angle. Therefore, the light illuminated onto the valleys of the fingerprint not in contact with the imaging surface 218 penetrates the imaging surface 218 and does not reach the image sensor 216. Meanwhile, the light illuminated onto the ridges of the fingerprint is scattered by the ridges.
  • Fig. 2B is a schematic diagram illustrating an operational principle of the fingerprint input apparatus of another scattering type.
  • the light illuminated onto the valleys of a fingerprint penetrates the imaging surface 318 and does not reach the image sensor 316.
  • the light illuminated onto the ridges of the fingerprint is scattered by the same principle.
  • the difference lies in using a prism of an isosceles triangular shape and changing the position of the backlight 312.
  • the light is absorbed at ridges of a fingerprint. Therefore, the image of the fingerprint appearing on the image sensor is dark at the ridges and bright at the valleys. In case of the fingerprint input apparatus of a scattering type, however, the light is scattered at ridges of a fingerprint. Therefore, the image of the fingerprint appearing on the image sensor is bright image at the ridges and dark at the valleys, thereby reflecting a comprehensively contrary image to the case of the fingerprint input apparatus of an absorption type.
  • an inversed image is displayed on the monitor of a computer in case of the finge ⁇ rint input apparatus of a scattering type.
  • the actual finge ⁇ rint image appearing on the image sensor is bright at the ridges and dark at the valleys of the fingerprint
  • the gray level in the course of processing the fingerprint image has a low value at the ridges and a high value at the valleys as in case of the fingerprint input apparatus of an absorption type.
  • the optical finge ⁇ rint input apparatus In case of the optical finge ⁇ rint input apparatus, however, sebum or a contaminated material leaves a latent finge ⁇ rint on the fingerprint recognition apparatus due to a contact of a fingerprint therewith. If a light is incident on the imaging surface from an external light, rather than from a backlight, at a particular angle, the image sensor is apt to sense a latent finge ⁇ rint. Thus, if the image sensor senses any latent fingerprint, the fingerprint recognition apparatus mis-recognizes the latent finge ⁇ rint as a fingerprint of a biomass. This causes a problem that an unauthorized user may be authenticated for access by using the latent fingerprint left on the fingerprint recognition apparatus instead of inputting a fingerprint of himself/herself.
  • Fig. 3 A shows an image of a normal fingerprint of a biomass
  • Fig. 3B shows a clear image of a latent fingerprint, which is quite similar to the one in Fig. 3A
  • Fig. 3C shows a vague image of a latent fingerprint.
  • the conventional art uses a method of storing a lastly inputted finge ⁇ rint of a person, comparing the stored fingerprint with a newly inputted fingerprint, and discriminates the newly inputted fingerprint as a latent fingerprint if the two fingerprints area quite similar (i.e., when the positions of a particular point of the two fingerprints coincide with each other or when comprehensive patterns of the two finge ⁇ rints overlap with each other).
  • this method still poses a problem that a pattern of the latent finge ⁇ rint read by the image sensor is variable due to a change of the external light, etc., and the stored pattern may be discriminated to be different from the latent fingerprint, thereby failing to discriminate a latent fingerprint on an accurate basis.
  • the present invention was conceived by an idea that a latent fingerprint can be detected due to an external light even when the backlight is off and not illuminated onto the fingerprint in the fingerprint input apparatus of an optical type. It is, therefore, an object of the present invention to provide a method and an apparatus for discriminating a latent fingerprint to discriminate a fingerprint detected by acquiring an image without illuminating an backlight onto an imaging surface to be a latent fingerprint detected due to an external light.
  • a method of discriminating a latent fingerprint in an optical fingerprint input apparatus comprising the steps of: acquiring an image without illuminating an backlight onto an imaging surface; detecting an existence of a fingerprint from the acquired image; and discriminating a detected finge ⁇ rint to be a latent fingerprint detected due to an external light.
  • an apparatus for discriminating a latent fingerprint in an optical fingerprint input apparatus comprising: backlight control means for controlling on/off of the backlight; image acquisition means for acquiring a fingerprint image without illuminating an backlight onto an imaging surface under a control by the backlight control means; fingerprint detection means for detecting an existence of a finge ⁇ rint from the image acquired by the image acquisition means; and latent fingerprint discrimination means for discriminating a fingerprint detected by the fingerprint detection means to be a latent fingerprint detected due to an external light.
  • a method of acquiring an entire frame of an image can be considered as a method of acquiring an image. Under an "off state of an backlight, an entire frame of an image is acquired and stored in a memory so that an existence of a latent fingerprint can be detected for the stored image.
  • a windowing function is provided for receiving an image at only a partial area of an image sensor depending on kinds thereof Therefore, it is possible to discriminate detection of a fingerprint by selectively acquiring a middle part of an image clearly reflecting the fingerprint when using an image sensor of this kind.
  • the fingerprint detection means comprises: calculating means for adding all the sums of the differences between gray levels of adjacent two pixels in an X direction or a Y direction of a coordinate for the acquired image; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected when the added value is greater than the reference value.
  • a fingerprint is clearly detected when an image has been acquired under an "off state of the backlight, the gray levels on the X axis (or on the Y axis) is varied in a wide range, and detection of a finge ⁇ rint is discriminated based on that variation.
  • a detected fingerprint is discriminated to be a latent fingerprint detected due to an external light.
  • the method of discriminating a fingerprint image by adding the differences in gray levels of adjacent pixels is a technology that can be easily carried out by one skilled in the art.
  • another method is also applicable for detecting an existence of a finge ⁇ rint by adding all the gray levels of each pixel, comparing the added value with a pre-set reference value, and discriminating that a fingerprint has been detected when the added value is less than the reference value.
  • Another method is still applicable for detecting an existence of a fingerprint by calculating an average value of the gray levels of pixels of an image and a dispersion value, and discriminating that a fingerprint has been detected when the average value is less than a first reference value and when the dispersion value is greater than a second reference value.
  • Other methods including this method are also well known to those skilled in the art.
  • the latent fingerprint discrimination means to first discriminate that the fingerprint is not a latent fingerprint in an absence of an incident external light but to mis-recognize the latent fingerprint as a fingerprint of a biomass when an external light is incident at the moment of illuminating an backlight and acquiring the finge ⁇ rint image.
  • the method of discriminating a latent finge ⁇ rint comprises the steps of: illuminating an backlight to the imaging surface and acquiring an image; switching off the backlight and acquiring an image when a fingerprint has been detected from the acquired image; and discriminating the detected fingerprint to be a latent fingerprint detected due to an external light when a fingerprint is detected under an "off state of the backlight.
  • the apparatus for discriminating a latent fingerprint comprises: backlight control means for controlling on and off of an backlight; image acquisition means for acquiring illuminating the backlight to an imaging surface under a control by the backlight control means to acquire an image; finge ⁇ rint detection means for detecting an existence of a fingerprint from the acquired image; wherein, if the fingerprint detection means has detected fingerprint, the image acquisition means re-acquire the image without illuminating the backlight onto the imaging surface; and latent fingerprint discrimination means for discriminating a fingerprint, if detected by the fingerprint acquisition means from the re-acquired image, to be a latent fingerprint detected due to an external light.
  • the methods for acquiring an image in the above method and apparatus can be performed similarly to the method of acquiring an image under an "off state of an backlight.
  • the available methods in this regard are to acquire an entire screen of an image or a partial image when an backlight is illuminated and not illuminated.
  • An existence of a fingerprint within the acquired image can also be detected by the same method as the one for detecting a finge ⁇ rint from an acquired image as described above.
  • an image acquired by using a method of receiving an image while switching "on” and “off the backlight in the course of acquiring the image contains a part acquired under illumination of the backlight and a part acquired under an "off state of the backlight that appear in turn.
  • a latent fingerprint can be discriminated by using this method of each part of the image. In other words, it can be discriminated to be a latent fingerprint if a fingerprint image is detected from the part of the image acquired under illumination of the backlight and a fingerprint image is detected from the part of the image acquired under an "off state of the backlight as well.
  • Fig. 1 is a schematic diagram illustrating an operational principle of a fingerprint input apparatus of an absorption type
  • Figs. 2A and 2B are schematic diagrams illustrating operational principles of a fingerprint input apparatus of an absorption type
  • Figs. 3A to 3C are exemplary patterns of a normal fingerprint and a latent finge ⁇ rint;
  • Fig. 4 is a flow chart illustrating a method of discriminating a latent fingerprint according to the present invention
  • Fig. 5 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a first best mode of the present invention
  • Fig. 6 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according a second best mode of the present invention
  • Fig. 7 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a third best mode of the present invention.
  • Fig. 8 is an exemplary pattern of a partial image acquired from the tip of a latent fingerprint
  • Fig. 9 is an exemplary pattern of a partial image acquired from a latent fingerprint by using a windowing function of an image sensor
  • Fig. 10 is a flow chart illustrating a method of discriminating a latent fingerprint according to a fourth best mode of the present invention
  • Fig. 11 is an exemplary pattern of a fingerprint image acquired by switching on and off an backlight
  • Fig. 12 is a block diagram illustrating a function of an apparatus for discriminating a latent fingerprint according to the present invention.
  • Fig. 4 is a flow chart illustrating a method of discriminating a latent fingerprint according to the present invention
  • Fig. 12 is a block diagram illustrating a function of an apparatus for discriminating a latent fingerprint according to the present invention. For the sake of convenience, the description of a method will be made along with an apparatus according to the present invention. If a person desiring to be authenticated for access touches an imaging surface with one of his/her fingers, backlight control means 503 switches off the backlight [SI 01].
  • Image acquisition means 505 then acquires an image of the fingerprint [S I 03], and fingerprint detection means 507 detects an existence of a fingerprint [SI 05].
  • latent fingerprint discrimination means 509 determines that a latent fingerprint has been detected due to an external light [SI 09]. If no fingerprint has been detected under an "off state of the backlight, the latent fingerprint discrimination means 509 discriminates the inputted fingerprint to be a fingerprint of a biomass [SI 09].
  • the fingerprint can be detected by adding gray levels of the image as described above. To be specific, differences in gray levels between adjacent pixels of the acquired image on the X axis or the Y axis of a coordinate are added, as shown in Fig. 5 [SI 06].
  • the latent fingerprint discrimination means discriminates whether the added value is greater or less than a pre-set reference value [SI 07]. Being greater means that a fingerprint has been detected under an "off state of the backlight, and it is discriminated that the acquired fingerprint image is a latent fingerprint [SI 08]. Being equal or less means that a fingerprint has not been detected [S I 13], and it is discriminated that the acquired fingerprint image is a fingerprint of a biomass.
  • Fig. 6 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according a second best mode of the present invention.
  • a fingerprint image is acquired by switching off the backlight, and all the gray level values of the pixels of the image are added [S206]. If the added value is less than the pre-set reference value, it means that a fingerprint has been detected [S208], and is discriminated that the acquired image is a latent finge ⁇ rint image.
  • Fig. 7 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a third best mode of the present invention.
  • a fingerprint image is acquired by switching off the backlight, and an average value M as well as a dispersion value D of the gray levels of the pixels of the image are calculated [S306]. If it is discriminated that M is less than a first reference value and that D is greater than a second reference value [S307], it means that a fingerprint has been detected [S308]. Therefore, it is discriminated that the acquired image is a latent fingerprint.
  • the above best mode represents a case of discriminating a latent fingerprint by acquiring an entire image of a fingerprint. It was mentioned above that time is wasted for the period of receiving a frame of the image in this case, and that time can be saved by acquiring only a part of the image, rather than the entire image, to discriminate a latent finge ⁇ rint under an "off state of an backlight.
  • Fig. 8 is an exemplary pattern of a half of the entire image acquired from a latent fingerprint.
  • a latent fingerprint can sufficiently be discriminated with only about half of the entire fingerprint image. The same method as described above is applied for discriminating a latent fingerprint.
  • Fig. 9 is an exemplary pattern of a mid-part image acquired from a latent fingerprint by using a windowing function of an image sensor.
  • a windowing function of the image sensor for receiving only a part of an image, the time consumed for receiving the finge ⁇ rint image will be reduced as the width W of the window is narrow, and as a consequence, the time consumed for discriminating a latent fingerprint will also be reduced.
  • Fig. 10 is a flow chart illustrating a method of discriminating a latent fingerprint according to a fourth best mode of the present invention.
  • Image acquisition means 505 switches on the backlight under a control by backlight control means 503 [S401] to acquire an image [S402].
  • fingerprint detection means 507 discriminates whether or not a fingerprint has been detected [S403]. In the affirmative, the image acquisition means 505 switches off the backlight under a control by the backlight control means 503 [S404] to acquire an image [S405]. The fingerprint detection means 507 then discriminates whether or not a fingerprint has been detected under an "off state of the backlight [S406].
  • discrimination means 509 discriminates the detected fingerprint to be a latent fingerprint [S407]. In the negative, the discrimination means 509 discriminates the detected fingerprint to be a fingerprint of a biomass [S408].
  • the same method as shown in Figs. 5 to 7 is used for detecting a fingerprint according to the fourth best mode, as in case of the third best mode.
  • an image is acquired under an "on” state of the backlight to detect an existence of a fingerprint, and an existence of a fingerprint is detected by acquiring an image under an "off state of the backlight when a fingerprint has been detected.
  • An image acquired by using a similar method of receiving an image while switching on and off the backlight in the course of acquiring the image contains a part acquired under an "on” state of the backlight and a part acquired under an "off state of the backlight that appear in turn.
  • Fig. 11 is an exemplary pattern of a fingerprint image acquired by switching on and off an backlight.
  • Part “A” represents an image acquired under an "off state of the backlight
  • part “B” represents an image acquired under an "on” state of the backlight.
  • the technical concept of the present invention lies in acquiring an image under an "off state of an backlight and discriminating a latent fingerprint from a fingerprint of a biomass based on the fingerprint image detected from the acquired image.

Abstract

Disclosed are a method and an apparatus for discriminating a latent fingerprint that can prevent a fingerprint recognition apparatus from mis-recognizing a latent fingerprint as a fingerprint of a biomass due to a fingerprint residual on an imaging surface of an optical fingerprint input apparatus. According to the present invention, there is provided backlight control means for controlling switching on and off of the backlight; image acquisition means for acquiring a fingerprint image without illuminating the backlight onto the imaging surface; fingerprint detection means for detecting an existence of a fingerprint from the image acquired by the image acquisition means; and fingerprint discriminating means for discriminating that the fingerprint, if detected by the fingerprint detection means, is a latent fingerprint detected due to an external light.

Description

METHOD AND APPARATUS FOR DISCRIMINATING LATENT FINGERPRINT IN OPTICAL FINGERPRINT INPUT APPARATUS
Technical Field This invention relates to a method and an apparatus for discriminating a latent fingerprint that can prevent a fingerprint recognition device from mis-recognizing a latent fingerprint as a fingerprint of a biomass due to a fingerprint residual on an imaging surface of an optical fingerprint input apparatus.
Background Art
A fingerprint recognition device can be utilized in a wide scale as a device for comparing and recognizing fingerprints between an inputted fingerprint and a pre- registered fingerprint of a user in the form of a locking device at a door or a safe, access control to a gate, attendance control of employees, access control to a computer, etc. The fingerprint input apparatuses for receiving fingerprints to perform such fingerprint recognition are mainly classified into two types: an optical type and a non-optical type. The fingerprint recognition device employing an optical fingerprint input apparatus is a device that illuminates a light to a fingerprint laid on a prism, interprets a fingerprint image reflected according to the shapes of valleys or ridges of the fingerprint and formed on an image sensor, and compares the interpreted image with a pre-stored fingerprint.
The optical fingerprint input apparatuses are mainly classified into an absorption type and a scattering type.
Fig. 1 is a schematic diagram illustrating an operational principle of a fingerprint input apparatus of an absorption type, which comprises a backlight 112, a triangular prism 110, a lens 114, an image sensor 116, and an image processor 125. The backlight 112 uses a plurality of LED aligned. The triangular prism 110 is a prism of a right triangular shape that generates a total reflection inside of an imaging surface when no fingerprint is inputted. The image sensor 116 is an element outputting electric signals corresponding to an amount of inputted light, such as a CCD or a CMOS sensor, well known to those skilled in the art. The inclined surface of the triangular prism 110 is an imaging surface, while an internal plane of the imaging surface 118 is a total reflection surface causing the total reflection.
Under no input of a fingerprint to the imaging surface 118, the light originating from the backlight 112 is totally reflected from inside of the imaging surface of the triangular prism 110, and is incident on the image sensor 116 through the lens 1 14. If a finger is laid on the imaging surface, the light illuminated onto the valleys of the fingerprint is totally reflected from the internal surface of the imaging surface 118 and reaches the image sensor 116 because the valleys of the fingerprint are not in contact with the imaging surface. By contrast, the light illuminated onto the ridges of the fingerprint is not totally reflected from the internal surface of the imaging surface 118 but only a part thereof reaches the image sensor 116.
Accordingly, the amounts of light incident on the image sensor 116 differ between the valleys and the ridges, and as a consequence, the image sensor 116 outputs electric signals of different levels depending on a pattern of a fingerprint. The image processor 125 formulates the output values of the image sensor 116 into digital signals so as to recognize a fingerprint pattern.
Figs. 2A and 2B are schematic diagrams illustrating an operational principle of a fingerprint input apparatus of a scattering type.
The fingerprint input apparatus in Fig. 2 A comprises a backlight 212, a prism 210, a lens 214, and a image sensor 216 to have a similar construction to the one in Fig. 1. However, the prism 210 is of a ladder shape rather than a triangular shape. Unlike the absorption type shown in Fig. 1 , the light is incident on the imaging surface 218 of the prism 210 from the backlight 211 at an angle far smaller than the right angle or a critical angle. Therefore, the light illuminated onto the valleys of the fingerprint not in contact with the imaging surface 218 penetrates the imaging surface 218 and does not reach the image sensor 216. Meanwhile, the light illuminated onto the ridges of the fingerprint is scattered by the ridges. The scattered light is incident on the lens 214, and is sensed by the image sensor 216. Fig. 2B is a schematic diagram illustrating an operational principle of the fingerprint input apparatus of another scattering type. As in case of Fig. 2A, the light illuminated onto the valleys of a fingerprint penetrates the imaging surface 318 and does not reach the image sensor 316. The light illuminated onto the ridges of the fingerprint is scattered by the same principle. However, the difference lies in using a prism of an isosceles triangular shape and changing the position of the backlight 312.
In case of the fingerprint input apparatus of an absorption type, the light is absorbed at ridges of a fingerprint. Therefore, the image of the fingerprint appearing on the image sensor is dark at the ridges and bright at the valleys. In case of the fingerprint input apparatus of a scattering type, however, the light is scattered at ridges of a fingerprint. Therefore, the image of the fingerprint appearing on the image sensor is bright image at the ridges and dark at the valleys, thereby reflecting a comprehensively contrary image to the case of the fingerprint input apparatus of an absorption type. To facilitate processing of the fingerprint image as well as to avoid an inversion of bright and dark images of a fingerprint appearing on a monitor of a computer depending on the input methods, an inversed image is displayed on the monitor of a computer in case of the fingeφrint input apparatus of a scattering type. To be specific, although the actual fingeφrint image appearing on the image sensor is bright at the ridges and dark at the valleys of the fingerprint, the gray level in the course of processing the fingerprint image has a low value at the ridges and a high value at the valleys as in case of the fingerprint input apparatus of an absorption type.
In case of the optical fingeφrint input apparatus, however, sebum or a contaminated material leaves a latent fingeφrint on the fingerprint recognition apparatus due to a contact of a fingerprint therewith. If a light is incident on the imaging surface from an external light, rather than from a backlight, at a particular angle, the image sensor is apt to sense a latent fingeφrint. Thus, if the image sensor senses any latent fingerprint, the fingerprint recognition apparatus mis-recognizes the latent fingeφrint as a fingerprint of a biomass. This causes a problem that an unauthorized user may be authenticated for access by using the latent fingerprint left on the fingerprint recognition apparatus instead of inputting a fingerprint of himself/herself.
Fig. 3 A shows an image of a normal fingerprint of a biomass, and Fig. 3B shows a clear image of a latent fingerprint, which is quite similar to the one in Fig. 3A. Fig. 3C shows a vague image of a latent fingerprint.
To solve this problem of mis-recognizing a latent fingerprint, the conventional art uses a method of storing a lastly inputted fingeφrint of a person, comparing the stored fingerprint with a newly inputted fingerprint, and discriminates the newly inputted fingerprint as a latent fingerprint if the two fingerprints area quite similar (i.e., when the positions of a particular point of the two fingerprints coincide with each other or when comprehensive patterns of the two fingeφrints overlap with each other). However, this method still poses a problem that a pattern of the latent fingeφrint read by the image sensor is variable due to a change of the external light, etc., and the stored pattern may be discriminated to be different from the latent fingerprint, thereby failing to discriminate a latent fingerprint on an accurate basis.
Disclosure of Invention The present invention was conceived by an idea that a latent fingerprint can be detected due to an external light even when the backlight is off and not illuminated onto the fingerprint in the fingerprint input apparatus of an optical type. It is, therefore, an object of the present invention to provide a method and an apparatus for discriminating a latent fingerprint to discriminate a fingerprint detected by acquiring an image without illuminating an backlight onto an imaging surface to be a latent fingerprint detected due to an external light.
To achieve the above object, there is provided a method of discriminating a latent fingerprint in an optical fingerprint input apparatus, the method comprising the steps of: acquiring an image without illuminating an backlight onto an imaging surface; detecting an existence of a fingerprint from the acquired image; and discriminating a detected fingeφrint to be a latent fingerprint detected due to an external light.
There is also provided an apparatus for discriminating a latent fingerprint in an optical fingerprint input apparatus, the apparatus comprising: backlight control means for controlling on/off of the backlight; image acquisition means for acquiring a fingerprint image without illuminating an backlight onto an imaging surface under a control by the backlight control means; fingerprint detection means for detecting an existence of a fingeφrint from the image acquired by the image acquisition means; and latent fingerprint discrimination means for discriminating a fingerprint detected by the fingerprint detection means to be a latent fingerprint detected due to an external light.
In the method and apparatus for discriminating a latent fingerprint, a method of acquiring an entire frame of an image can be considered as a method of acquiring an image. Under an "off state of an backlight, an entire frame of an image is acquired and stored in a memory so that an existence of a latent fingerprint can be detected for the stored image.
However, use of the above method of acquiring an image wastes a time for acquiring an entire frame of an image to discriminate a latent fingerprint. Therefore, time can be saved if a latent fingerprint is discriminated by acquiring a partial frame of a fingerprint image without illuminating the backlight and by using the partial frame of the image.
Here, in case when a finger is small or when a fingerprint is in contact with a lower part of the imaging surface, it is desirable to acquire a fingerprint image of about 1/4 to 1/2 from the tip of the fingerprint image. Meanwhile, a windowing function is provided for receiving an image at only a partial area of an image sensor depending on kinds thereof Therefore, it is possible to discriminate detection of a fingerprint by selectively acquiring a middle part of an image clearly reflecting the fingerprint when using an image sensor of this kind.
Detection of an existence of a fingerprint is made by the fingerprint detection means. The fingerprint detection means comprises: calculating means for adding all the sums of the differences between gray levels of adjacent two pixels in an X direction or a Y direction of a coordinate for the acquired image; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected when the added value is greater than the reference value. To be specific, if a fingerprint is clearly detected when an image has been acquired under an "off state of the backlight, the gray levels on the X axis (or on the Y axis) is varied in a wide range, and detection of a fingeφrint is discriminated based on that variation. A detected fingerprint is discriminated to be a latent fingerprint detected due to an external light. The method of discriminating a fingerprint image by adding the differences in gray levels of adjacent pixels is a technology that can be easily carried out by one skilled in the art.
In addition to the above method, another method is also applicable for detecting an existence of a fingeφrint by adding all the gray levels of each pixel, comparing the added value with a pre-set reference value, and discriminating that a fingerprint has been detected when the added value is less than the reference value.
Another method is still applicable for detecting an existence of a fingerprint by calculating an average value of the gray levels of pixels of an image and a dispersion value, and discriminating that a fingerprint has been detected when the average value is less than a first reference value and when the dispersion value is greater than a second reference value. Other methods including this method are also well known to those skilled in the art.
When the above method is used, however, an image is acquired without an backlight illuminated onto the imaging surface, and a user is unable to ascertain whether or not the fingerprint input apparatus is in operation. Furthermore, it is still possible, though rare, for the latent fingerprint discrimination means to first discriminate that the fingerprint is not a latent fingerprint in an absence of an incident external light but to mis-recognize the latent fingerprint as a fingerprint of a biomass when an external light is incident at the moment of illuminating an backlight and acquiring the fingeφrint image.
To resolve this problem, another method has been suggested to acquire an image by illuminating an backlight, and when a fingerprint has been detected, switch off the backlight and acquire the image. If a fingerprint is detected under this state, it is discriminated to be a latent fingerprint. Otherwise, it is discriminated to be a fingeφrint of a biomass. In this case, the method of discriminating a latent fingeφrint comprises the steps of: illuminating an backlight to the imaging surface and acquiring an image; switching off the backlight and acquiring an image when a fingerprint has been detected from the acquired image; and discriminating the detected fingerprint to be a latent fingerprint detected due to an external light when a fingerprint is detected under an "off state of the backlight.
In that case, the apparatus for discriminating a latent fingerprint comprises: backlight control means for controlling on and off of an backlight; image acquisition means for acquiring illuminating the backlight to an imaging surface under a control by the backlight control means to acquire an image; fingeφrint detection means for detecting an existence of a fingerprint from the acquired image; wherein, if the fingerprint detection means has detected fingerprint, the image acquisition means re-acquire the image without illuminating the backlight onto the imaging surface; and latent fingerprint discrimination means for discriminating a fingerprint, if detected by the fingerprint acquisition means from the re-acquired image, to be a latent fingerprint detected due to an external light. The methods for acquiring an image in the above method and apparatus can be performed similarly to the method of acquiring an image under an "off state of an backlight. The available methods in this regard are to acquire an entire screen of an image or a partial image when an backlight is illuminated and not illuminated.
An existence of a fingerprint within the acquired image can also be detected by the same method as the one for detecting a fingeφrint from an acquired image as described above.
Also, an image acquired by using a method of receiving an image while switching "on" and "off the backlight in the course of acquiring the image contains a part acquired under illumination of the backlight and a part acquired under an "off state of the backlight that appear in turn. A latent fingerprint can be discriminated by using this method of each part of the image. In other words, it can be discriminated to be a latent fingerprint if a fingerprint image is detected from the part of the image acquired under illumination of the backlight and a fingerprint image is detected from the part of the image acquired under an "off state of the backlight as well. In the opposite case, it can be discriminated to be a fingerprint of a biomass if a fingeφrint image is detected from the part of the image acquired under illumination of the backlight and no fingerprint image is detected from the part of the image acquired under an "off state of the backlight.
Brief Description of Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a schematic diagram illustrating an operational principle of a fingerprint input apparatus of an absorption type;
Figs. 2A and 2B are schematic diagrams illustrating operational principles of a fingerprint input apparatus of an absorption type;
Figs. 3A to 3C are exemplary patterns of a normal fingerprint and a latent fingeφrint; Fig. 4 is a flow chart illustrating a method of discriminating a latent fingerprint according to the present invention;
Fig. 5 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a first best mode of the present invention; Fig. 6 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according a second best mode of the present invention;
Fig. 7 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a third best mode of the present invention;
Fig. 8 is an exemplary pattern of a partial image acquired from the tip of a latent fingerprint;
Fig. 9 is an exemplary pattern of a partial image acquired from a latent fingerprint by using a windowing function of an image sensor;
Fig. 10 is a flow chart illustrating a method of discriminating a latent fingerprint according to a fourth best mode of the present invention; Fig. 11 is an exemplary pattern of a fingerprint image acquired by switching on and off an backlight; and
Fig. 12 is a block diagram illustrating a function of an apparatus for discriminating a latent fingerprint according to the present invention.
Best Modes for Carrying out the Invention
Best modes for carrying out the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Fig. 4 is a flow chart illustrating a method of discriminating a latent fingerprint according to the present invention, and Fig. 12 is a block diagram illustrating a function of an apparatus for discriminating a latent fingerprint according to the present invention. For the sake of convenience, the description of a method will be made along with an apparatus according to the present invention. If a person desiring to be authenticated for access touches an imaging surface with one of his/her fingers, backlight control means 503 switches off the backlight [SI 01]. Image acquisition means 505 then acquires an image of the fingerprint [S I 03], and fingerprint detection means 507 detects an existence of a fingerprint [SI 05]. As described above, if a fingeφrint has been detected under an "off state of an backlight, latent fingerprint discrimination means 509 determines that a latent fingerprint has been detected due to an external light [SI 09]. If no fingerprint has been detected under an "off state of the backlight, the latent fingerprint discrimination means 509 discriminates the inputted fingerprint to be a fingerprint of a biomass [SI 09].
In step [105] of detecting a fingerprint, the fingerprint can be detected by adding gray levels of the image as described above. To be specific, differences in gray levels between adjacent pixels of the acquired image on the X axis or the Y axis of a coordinate are added, as shown in Fig. 5 [SI 06].
As a next step, the latent fingerprint discrimination means discriminates whether the added value is greater or less than a pre-set reference value [SI 07]. Being greater means that a fingerprint has been detected under an "off state of the backlight, and it is discriminated that the acquired fingerprint image is a latent fingerprint [SI 08]. Being equal or less means that a fingerprint has not been detected [S I 13], and it is discriminated that the acquired fingerprint image is a fingerprint of a biomass.
Fig. 6 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according a second best mode of the present invention. A fingerprint image is acquired by switching off the backlight, and all the gray level values of the pixels of the image are added [S206]. If the added value is less than the pre-set reference value, it means that a fingerprint has been detected [S208], and is discriminated that the acquired image is a latent fingeφrint image.
Fig. 7 is a flow chart illustrating a process of discriminating whether or not a fingerprint exists according to a third best mode of the present invention. A fingerprint image is acquired by switching off the backlight, and an average value M as well as a dispersion value D of the gray levels of the pixels of the image are calculated [S306]. If it is discriminated that M is less than a first reference value and that D is greater than a second reference value [S307], it means that a fingerprint has been detected [S308]. Therefore, it is discriminated that the acquired image is a latent fingerprint.
The above best mode represents a case of discriminating a latent fingerprint by acquiring an entire image of a fingerprint. It was mentioned above that time is wasted for the period of receiving a frame of the image in this case, and that time can be saved by acquiring only a part of the image, rather than the entire image, to discriminate a latent fingeφrint under an "off state of an backlight.
Fig. 8 is an exemplary pattern of a half of the entire image acquired from a latent fingerprint. A latent fingerprint can sufficiently be discriminated with only about half of the entire fingerprint image. The same method as described above is applied for discriminating a latent fingerprint.
Fig. 9 is an exemplary pattern of a mid-part image acquired from a latent fingerprint by using a windowing function of an image sensor. When using such a windowing function of the image sensor for receiving only a part of an image, the time consumed for receiving the fingeφrint image will be reduced as the width W of the window is narrow, and as a consequence, the time consumed for discriminating a latent fingerprint will also be reduced.
Fig. 10 is a flow chart illustrating a method of discriminating a latent fingerprint according to a fourth best mode of the present invention. Image acquisition means 505 switches on the backlight under a control by backlight control means 503 [S401] to acquire an image [S402]. As a next step, fingerprint detection means 507 discriminates whether or not a fingerprint has been detected [S403]. In the affirmative, the image acquisition means 505 switches off the backlight under a control by the backlight control means 503 [S404] to acquire an image [S405]. The fingerprint detection means 507 then discriminates whether or not a fingerprint has been detected under an "off state of the backlight [S406]. In the affirmative, discrimination means 509 discriminates the detected fingerprint to be a latent fingerprint [S407]. In the negative, the discrimination means 509 discriminates the detected fingerprint to be a fingerprint of a biomass [S408]. The same method as shown in Figs. 5 to 7 is used for detecting a fingerprint according to the fourth best mode, as in case of the third best mode.
In the fourth best mode shown in Fig. 10, an image is acquired under an "on" state of the backlight to detect an existence of a fingerprint, and an existence of a fingerprint is detected by acquiring an image under an "off state of the backlight when a fingerprint has been detected. An image acquired by using a similar method of receiving an image while switching on and off the backlight in the course of acquiring the image contains a part acquired under an "on" state of the backlight and a part acquired under an "off state of the backlight that appear in turn.
Fig. 11 is an exemplary pattern of a fingerprint image acquired by switching on and off an backlight. Part "A" represents an image acquired under an "off state of the backlight, while part "B" represents an image acquired under an "on" state of the backlight. As described above, it is discriminated that an image was acquired from a fingeφrint of a biomass because a fingeφrint has not been detected in the part "A", which was acquired under an "off state of the backlight, but has been detected in the part "B", which was acquired under an "on" state of the backlight.
It is well known to those skilled in the pertinent art that switching on and off of the backlight is controlled by software, and that the image part acquired under an "on" state of the backlight is discriminated from the image part acquired under an "off state of the backlight by calculation.
While the invention has been shown and described with reference to certain best modes to carry out the invention, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The technical concept of the present invention lies in acquiring an image under an "off state of an backlight and discriminating a latent fingerprint from a fingerprint of a biomass based on the fingerprint image detected from the acquired image.

Claims

What Is Claimed Is:
1. A method of discriminating a latent fingerprint residual on an imaging surface of an optical fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingeφrint and reflected therefrom, the method comprising the steps of: acquiring an image without illuminating the backlight onto the imaging surface; detecting an existence of a fingerprint from the acquired image; and discriminating the fingerprint, if detected, to be a latent fingerprint detected due to an external light.
2. The method of claim 1 , wherein the step of acquiring an image is performed by receiving an entire screen of an image.
3. The method of claim 1 , wherein the step of acquiring an image is performed by receiving only a part of an image from the tip thereof.
4. The method of claim 1 , wherein the step of acquiring an image is performed by receiving only a part of an image by using a windowing function of an image sensor.
5. The method of any one of claims 1 to 4, wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating a sum of differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingeφrint has been detected if the sum of the gray levels is greater than the reference value.
6. The method of any one of claims 1 to 4, wherein the step of detecting an existence of a fingeφrint comprises the sub-steps of: calculating a sum of differences between gray levels with respect to the acquired image; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingerprint has been detected if the sum of the gray levels is less than the reference value.
7. The method of any one of claims 1 to 4, wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
8. A method of discriminating a latent fingerprint residual on an imaging surface of an optical fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingerprint and reflected therefrom, the method comprising the steps of: acquiring an image by illuminating an backlight onto the imaging surface: detecting an existence of a fingerprint from the acquired image; acquiring an image under an "off state of the backlight if a fingerprint has been detected; detecting an existence of a fingerprint from the acquired image; and discriminating that the fingerprint, if detected, is a latent fingerprint detected due to an external light.
9. The method of claim 8, wherein the step of acquiring an image is performed by receiving an entire screen of an image.
10. The method of claim 8, wherein the step of acquiring an image is performed by receiving only a part of an image from the tip thereof.
11. The method of claim 8, wherein the step of acquiring an image is performed by receiving only a part of an image by using a windowing function of an image sensor.
12. The method of any one of claims 8 to 11, wherein the step of detecting an existence of a fingeφrint comprises the sub-steps of: calculating a sum of differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingeφrint has been detected if the sum of the gray levels is greater than the reference value.
13. The method of any one of claims 8 to 1 1 , wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating a sum of differences between gray levels with respect to the acquired image; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingerprint has been detected if the sum of the gray levels is less than the reference value.
14. The method of any one of claims 8 to 1 1 , wherein the step of detecting an existence of an fingeφrint comprises the sub-steps of: calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
15. A method of discriminating a latent fingeφrint residual on an imaging surface of an optical fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingerprint and reflected therefrom, the method comprising the steps of: acquiring an image while switching on and off the backlight onto the imaging surface; detecting an existence of a fingerprint with respect to the image part acquired under an "on" state of the backlight; detecting an existence of a fingerprint with respect to the image part acquired under an "off state of the backlight; and discriminating that the fingerprint, if detected from both image parts acquired under an "on" state and "off state of the backlight, is a latent fingerprint detected due to an external light.
16. The method of claim 15, wherein the step of acquiring an image is performed by receiving an entire screen of an image.
17. The method of claim 15, wherein the step of acquiring an image is performed by receiving only a part of an image from the tip thereof.
18. The method of claim 15, wherein the step of acquiring an image is performed by receiving only a part of an image by using a windowing function of an image sensor.
19. The method of any one of claims 15 to 18, wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating a sum of differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingerprint has been detected if the sum of the gray levels is greater than the reference value.
20. The method of any one of claims 15 to 18, wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating a sum of differences between gray levels with respect to the acquired image; comparing the calculated sum of the gray levels with a pre-set reference value; and discriminating that a fingerprint has been detected if the sum of the gray levels is less than the reference value.
21. The method of any one of claims 15 to 18, wherein the step of detecting an existence of a fingerprint comprises the sub-steps of: calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
22. An apparatus for discriminating a latent fingeφrint residual on an imaging surface of a fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingerprint and reflected therefrom, the apparatus comprising: backlight control means for controlling switching on and off of the backlight; image acquisition means for acquiring a fingeφrint image without illuminating the backlight onto the imaging surface; fingerprint detection means for detecting an existence of a fingerprint from the image acquired by the image acquisition means; and fingerprint discriminating means for discriminating that the fingerprint, if detected by the fingerprint detection means, is a latent fingerprint detected due to an external light.
23. The apparatus of claim 22, wherein the image acquisition means receives an entire screen of an image.
24. The apparatus of claim 22, wherein the image acquisition means receives only a part of an image from the tip thereof.
25. The apparatus of claim 22, wherein the image acquisition means receives only a part of an image by using a windowing function of an image sensor.
26. The apparatus of any one of claims 22 to 25, wherein the fingerprint detection means comprises: calculating means for adding differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is less than the pre-set reference value.
27. The apparatus of any one of claims 22 to 25, wherein the fingerprint detection means comprises: calculating means for adding gray levels with respect to the acquired image; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is less than the pre-set reference value.
28. The apparatus of any one of claims 22 to 25, wherein the fingerprint detection means comprises: calculating means for calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating means for discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
29. An apparatus for discriminating a latent fingerprint residual on an imaging surface of an optical fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingerprint and reflected therefrom, the apparatus comprising: backlight control means for controlling switching on and off of the backlight; image acquisition means for acquiring a fingerprint image without illuminating an backlight onto an imaging surface under a control by the backlight control means; fingerprint detection means for detecting an existence of a fingerprint from the image acquired by the image acquisition means; wherein, if the fingerprint detection means has detected fingerprint, the image acquisition means re-acquire the image without illuminating the backlight onto the imaging surface; and latent fingerprint discrimination means for discriminating a fingerprint, if detected by the fingerprint acquisition means from the re-acquired image, to be a latent fingerprint detected due to an external light.
30. The apparatus of claim 29, wherein the image acquisition means receives an entire screen of an image.
31. The apparatus of claim 29, wherein the image acquisition means receives only a part of an image from the tip thereof.
32. The apparatus of claim 29, wherein the image acquisition means receives only a part of an image by using a windowing function of an image sensor.
33. The apparatus of any one of claims 29 to 32, wherein the fingerprint detection means comprises: calculating means for adding differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is greater than the pre-set reference value.
34. The apparatus of any one of claims 29 to 32, wherein the fingerprint detection means comprises: calculating means for adding gray levels with respect to the acquired image; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is less than the pre-set reference value.
35. The apparatus of any one of claims 29 to 32, wherein the fingerprint detection means comprises: calculating means for calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating means for discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
36. An apparatus for discriminating a latent fingerprint residual on an imaging surface of an optical fingerprint input apparatus, which acquires a fingerprint image by an backlight illuminated onto a fingerprint and reflected therefrom, the apparatus comprising: backlight control means for controlling switching on and off of the backlight; image acquisition means for acquiring an image acquiring an image while switching on and off the backlight onto the imaging surface; fingerprint detection means for detecting an existence of a fingerprint with respect to the image parts acquired under an "on" state of the backlight and under an "off state of the backlight, respectively; and latent fingerprint discriminating means for discriminating that the fingerprint, if detected from both image parts acquired under an "on" state and "off state of the backlight, is a latent fingerprint detected due to an external light.
37. The apparatus of claim 36, wherein the image acquisition means receives an entire screen of an image.
38. The apparatus of claim 36, wherein the image acquisition means receives only a part of an image from the tip thereof.
39. The apparatus of claim 36, wherein the image acquisition means receives only a part of an image by using a windowing function of an image sensor.
40. The apparatus of any one of claims 36 to 39, wherein the fingerprint detection means comprises: calculating means for adding differences between gray levels of adjacent pixels of the acquired image on an X axis or a Y axis of a coordinate; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is greater than the pre-set reference value.
41. The apparatus of any one of claims 36 to 39, wherein the fingerprint detection means comprises: calculating means for adding gray levels with respect to the acquired image; comparing means for comparing the added value with a pre-set reference value; and discriminating means for discriminating that a fingerprint has been detected if the added value is less than the pre-set reference value.
42. The apparatus of any one of claims 36 to 39, wherein the fingerprint detection means comprises: calculating means for calculating an average value and a dispersion value of gray levels with respect to the acquired image; and discriminating means for discriminating that a fingerprint has been detected if the calculated average value is less than a first reference value and the calculated dispersion value is greater than a second reference value.
PCT/KR2001/000708 2000-04-29 2001-04-27 Method and apparatus for discriminating latent fingerprint in optical fingerprint input apparatus WO2001084477A1 (en)

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US20050141756A1 (en) 2005-06-30
KR20010105426A (en) 2001-11-29
CN100380389C (en) 2008-04-09
KR100333138B1 (en) 2002-04-19
US20040026635A1 (en) 2004-02-12
JP2003532240A (en) 2003-10-28
CN1451141A (en) 2003-10-22
US20050141755A1 (en) 2005-06-30
US6989547B2 (en) 2006-01-24
US6885017B2 (en) 2005-04-26
US6995384B2 (en) 2006-02-07

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