1. Field of the Invention
The present invention relates generally to eliminating the effects of ambient light (indoor or outdoor) on an image.
2. Background Art
Biometrics is the science and technology of authentication (i.e. establishing the identity of an individual) by measuring the person's physiological or behavioral features. The term is derived from the Greek words “bios” for life and “metron” for degree.
In information technology, biometrics usually refers to technologies for measuring and analyzing human physiological characteristics such as fingerprints, eye retinas and irises, voice patterns, facial patterns, and hand measurements; especially for authentication purposes.
In a typical biometric system, a person registers with the system when one or more of their physiological characteristics are obtained, processed by a numerical algorithm, and entered into a database. Ideally, when the person logs into the system at a later time all of their features match. If someone else tries to log in as the same person, their biometric information does not fully match, so the system will not allow them to log in.
Performance of a biometric system is usually referred to in terms of the false accept rate (FAR), the false non-match or reject rate (FRR), and the failure to enroll rate (FTE or FER). In real-world biometric systems the FAR and FRR can typically be traded off against each other by changing parameters. One of the most common measures of real-world biometric systems is the rate at the setting at which both accept and reject errors are equal: the equal error rate (EER), also known as the cross-over error rate (CER). The lower the EER or CER, the more accurate the system is considered to be. Current technologies have widely varying Equal Error Rates (EER) from as low as 60% to as high as 99.9%.
Among all the biometric techniques, fingerprint-based identification is one of the oldest and most accurate methods which has been successfully used in numerous applications. Everyone is known to have unique, immutable fingerprints. A fingerprint is made of a series of ridges and furrows on the surface of the finger. The uniqueness of a fingerprint can be determined by the pattern of ridges and furrows as well as the minutiae points. Minutiae points are local ridge characteristics that occur at either a ridge bifurcation or a ridge ending. To implement fingerprint-based identification, an image or imprint of the fingerprint has to be acquired.
Similarly, an image of any uniquely identifiable skin surface can be used for identification. In addition to a single fingerprint, multiple fingertip images can be used for this purpose. In addition, images of the palm or the entire hand can be used as biometric identifiers.
In each of these identifying methods, a scanning process is used to acquire data representing a person's skin pattern characteristics. This allows the recognition of a person through quantifiable physiological characteristics that verify the identity of an individual. Optical methods are often used to obtain a visual image of the surface data of interest. In the case of fingerprint identification, a common optical data capture method includes placing one or more fingertips on a translucent platen. Beneath the platen, light reflected from the fingertips is directed through an optical path to an imaging device that captures image data.
However, the inventors have found that ambient light, which might be natural or artificial, often interferes with the acquisition of an optical image of a fingerprint. Therefore, there is a need for an improved fingerprint sensor system that overcomes the imaging problems created by the presence of various forms of ambient light.
A method for obtaining an improved optical image of a fingerprint overcomes degradation of the quality and contrast of the image by minimizing the effects of ambient light. In an exemplary embodiment, the method comprises illuminating an object to be imaged with light that includes a predetermined wavelength, filtering the reflection with a band pass filter that passes the predetermined wavelength, and capturing the image with an image sensor.
In an embodiment, an optical sub-system between a skin surface and an image sensor includes an illumination source enabled to emit light including a predetermined wavelength onto the skin surface, and a filter disposed in the optical path created by the optical sub-system between the skin surface and the image sensor and enabled to pass the reflection of the predetermined wavelength.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Neither the summary nor the detailed description are intended to limit the scope of the claims in any way.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention will now be described with reference to the accompanying drawings. In the drawings, some like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of most reference numbers identify the drawing in which the reference numbers first appear.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility.
The present invention will be described in terms of an embodiment applicable to fingerprint scanning and overcoming imaging problems created by the presence of various forms of ambient light. It will be understood that the essential fingerprint scanning concepts disclosed herein are applicable to a wide range of skin surface imaging technologies, biometric systems, architectures and optical hardware elements. Thus, although the invention will be disclosed and described in terms of examples in the field of enhancing the quality of a fingerprint image by overcoming the effects of ambient light, the invention is not limited to this field.
Embodiments of the present invention provide, among other things, improved apparatus and methods for substantially eliminating the effects of ambient light (indoor or outdoor) on a fingerprint image. Exemplary embodiments will now be described in detail with reference to the drawings.
Terminology
To more clearly delineate the present invention, an effort is made throughout the specification to adhere to the following term definitions consistently.
The term “finger” refers to any digit on a hand including, but not limited to, a thumb, an index finger, middle finger, ring finger, or a pinky finger.
The term “skin surface” includes but is not limited to the surface of one or more fingers, palms, toes, foot, hand, palm, etc.
The term “print” can be any type of print including, but not limited to, a print of all or part of one or more fingers, palms, toes, foot, hand, etc. A print can also be a rolled print, a flat print, or a slap print.
The term “hand print,” can include any region on a hand having a print pattern, including thenar and hypothenar regions of the palm, interdigital regions, palm heel, palm pocket, writer's palm, and/or fingertips.
The term “live scan” refers to a capture of any type of print image made by a print scanner.
The term “non-planar prism” includes a prism having a non-planar platen surface that extends around all or part of an axis of the prism, and whose non-planar platen surface allows for total internal reflection of light. A non-planar platen surface allows a print pattern (such as, a print pattern on a hand, a palm pocket, a writer's palm, a writer's palm with fingertips), or other hand characteristic images, to be captured. An example of this type of prism can be an approximately conically-shaped prism. Other examples can be approximately spherically shaped prisms, curved prisms, and the like.
A platen can be movable or stationary depending upon the particular type of scanner and the type of print being captured by the scanner.
The terms “fingerprint scanner”, “scanner”, “live scanner”, “live print scanner,” and “print scanner” are interchangeable, and refer to any type of scanner which can obtain an image of a print pattern on all or part of one or more fingers, palms, toes, feet, hands, etc. in a live scan. The obtained images can be combined in any format including, but not limited to, an FBI, state, or international ten print format.
Example Fingerprint Scanning System
The fingerprint scanner 100 in
Where the ridges 108 of a finger 114 contact platen surface 110, the TIR of prism 112 is broken. The light from illumination source 102 escapes the prism and enters the finger, where a significant amount of the light is absorbed. For the fingerprint valleys (areas of the fingerprint where air contacts the platen surface) the illumination source 102 will stay in TIR. These light rays continue through optical sub-system 106 and are focused onto image sensor 104. The optical sub-system 106 may consist of focusing lenses 116 and a mirror 118. The difference between (a) the light reflected off the internal surface of platen 110 onto image sensor 104 and (b) the light absorbed by fingerprint ridges 108 creates the contrast necessary to accurately reproduce a fingerprint image onto image sensor 104.
The image sensor 104 may be a charge coupled device (CCD) as is used in digital cameras and camcorders. A CCD is simply an array of light-sensitive diodes called photosites, which generate an electrical signal in response to light photons. Each photosite records a pixel, a tiny dot representing the light that hit that spot. Collectively, the light and dark pixels form an image of the scanned finger. Typically, an analog-to-digital converter in a scanner system 100 processes the analog electrical signal to generate a digital representation of this image. The image sensor 104 generates an image of the finger. Dark areas represent the ridges of the finger and lighter areas represent valleys between the ridges. Such bright-field illumination is illustrative and not intended to limit the present invention. Other illumination systems may be used including, but not limited to, other bright-field or dark-field types of illumination systems.
The inventors have determined that fingerprint scanning systems of the type shown in
In one embodiment, the described method operates with a fingerprint scanner using a bright field illumination method. As seen in
The embodiment shown in
In another embodiment, band pass filter 302 and IR cutoff filter 304 are combined as a single optical element. In yet another embodiment, infrared cutoff filter 304 is implemented using a cold reflector mirror. In another optional embodiment, filters 302 and 304 are implemented using optical coatings on prism 112, one or more optical elements in optical sub-system 106, or image sensor 104. It is important to note that the mirror 118, lenses 116 and the illumination system in this example are only drawn to illustrate one such method for implementation.
In another embodiment, it is possible to use a non-planar prism instead of a planar prism 112. In yet another embodiment, the skin surface being imaged need not be placed on a platen surface 110 that requires physical contact.
In other embodiments, the image sensor 104 may be a phototransistor, a Contact Image Sensor (CIS), a Complimentary Metal Oxide Semiconductor (CMOS) or any other device capable of capturing skin surface pattern data focused on it via optical sub-system 106.
In a preferred embodiment an illumination source 102 of green light is used since the finger 114 absorbs more light at shorter wavelengths. In other embodiments light of a different wavelength/color that is substantially absorbed by finger 114 or another skin surface may be used. In another embodiment, if an illumination source 102 of a different wavelength/color is used, a band pass filter 302 corresponding to that wavelength/color will have to be used in conjunction with it.
The illumination source 102 in the current embodiment may be an array of light-emitting diodes (LEDs) that emit monochromatic light in a desired wavelength range. In other embodiments, the illumination source 102 may be another light source capable of emitting monochromatic light such as a laser light source. In the physical sense however, no real source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration. Even sources such as lasers have some narrow range of wavelengths within which they operate.
In the current embodiment the optical sub-system 106 consists of lenses 116 and mirror 118. In other embodiments the optical sub-system 106 may consist of the prism 112 and/or the optical filters 302 and 304 as shown in
While the embodiment presented herein uses a fingerprint as an example, it is obvious to a person skilled in the relevant art(s) to apply it to hand prints or any other skin surface pattern data. The embodiments presented use a planar prism 112 but it is obvious to a person skilled in the relevant art(s) to use any optical device (such as a non-planar prism, holographic optical element, or other means) that allows TIR for a fingerprint image to travel from the surface of finger 114 to the image sensor 104 along an optical path provided by optical sub-system 106.
Green band pass filter 302 is illustrative. Any short-wavelength band pass filter can be used that passes light having a wavelength shorter than red light. For example, a band pass filter that passes light having a wavelength less than about 600 nanometers (nm.) can be used. Such a band pass filter can include but is not limited to an amber band pass filter, amber/green band pass filter, green band pass filter or other shorter wavelength band pass filter.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the patent claims and their equivalents.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/566,175, filed Apr. 29, 2004, incorporated herein by reference in its entirety.
Number | Date | Country | |
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60566175 | Apr 2004 | US |