LARGE DEPTH-OF-FIELD IMAGING SYSTEM AND IRIS RECOGNITON SYSTEM
First Claim
1. An iris-recognition (I-R) system for capturing images of one or both irises of a person over a large depth of field (DOF), comprising:
- an illumination system adapted to i) illuminate at an imaging wavelength λ
IM a facial region of the person, wherein the facial region includes one or both eyes and at least a forehead portion of the person, and ii) to form a spot on the forehead portion;
an optical system having an object plane within the large depth of field DOF, an image plane within a correspondingly large depth of focus DOF′
with an image sensor arranged thereat, and an amount of spherical aberration (SA) at an imaging wavelength λ
IM such that the depth of field DOF increases by an amount between 50% and 500% as compared to the optical system being diffraction limited, the optical system configured to form on the image sensor an image of the facial region when the facial region is placed within the depth of field DOF, wherein said facial region image includes an image of the forehead spot; and
a controller electrically connected to the image sensor and to the illumination system, the controller adapted to control and coordinate the operation of the illumination system and the image sensor, and adapted to perform image-processing on the facial-region image to form an enhanced image of one or both irises based on an enhanced modulation transfer function (MTF) formed using forehead distance information obtained from the forehead spot.
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Abstract
(A2) An extended depth of field (DOF) imaging system (10) is disclosed that has a corresponding extended depth of focus (DOF′) by virtue of its optical system (20) having a select amount of spherical aberration. The imaging system has an image processing unit (54) adapted to process the raw images and perform contrast enhancement to form processed images. The image processing includes restoring the defocused modulation transfer functions (MTFs) using a gain function (G) and the amount of defocus. The imaging system can include an illumination system (60) that illuminates the object being imaged to establish a distance (DH) between the optical system and the object, where distance DH is used in the restoring of the MTF. An iris-recognition (I-R) system based on the enhanced DOF imaging system is also disclosed.; Optical system embodiments for use in the DOF imaging system that can provide select amounts of spherical aberration—and thus select increases in DOF—without increasing the adverse impact of other aberrations on image formation are also disclosed.
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Citations
38 Claims
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1. An iris-recognition (I-R) system for capturing images of one or both irises of a person over a large depth of field (DOF), comprising:
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an illumination system adapted to i) illuminate at an imaging wavelength λ
IM a facial region of the person, wherein the facial region includes one or both eyes and at least a forehead portion of the person, and ii) to form a spot on the forehead portion;an optical system having an object plane within the large depth of field DOF, an image plane within a correspondingly large depth of focus DOF′
with an image sensor arranged thereat, and an amount of spherical aberration (SA) at an imaging wavelength λ
IM such that the depth of field DOF increases by an amount between 50% and 500% as compared to the optical system being diffraction limited, the optical system configured to form on the image sensor an image of the facial region when the facial region is placed within the depth of field DOF, wherein said facial region image includes an image of the forehead spot; anda controller electrically connected to the image sensor and to the illumination system, the controller adapted to control and coordinate the operation of the illumination system and the image sensor, and adapted to perform image-processing on the facial-region image to form an enhanced image of one or both irises based on an enhanced modulation transfer function (MTF) formed using forehead distance information obtained from the forehead spot. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of forming an enhanced image of at least one iris of a person, comprising:
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forming a raw image of a facial region of the person that includes at least one eye of the person and a forehead portion of the person using an optical system having an amount of spherical aberration that increases a depth of field (DOF) of the optical system by an amount between 50% and 500% as compared to the optical system being diffraction limited; using an image sensor, electronically capturing the raw image to form a digitized raw image, the raw image having a corresponding raw modulation transfer function (MTF); establishing an amount of defocus in the digitized raw image based on a position of the person relative to the optical system; forming an enhanced MTF from the raw MTF by multiplying the raw MTF by a gain function, wherein the enhanced MTF is a function of the amount of defocus; and applying the enhanced MTF to the digitized raw image to obtain the enhanced image. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. An enhanced depth of field (DOE) imaging system for forming an enhanced contrast image of an object, comprising:
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an optical system having an amount of spherical aberration (SA) at an imaging wavelength λ
IM such that the depth of field DOF increases by an amount between 50% and 500% as compared to the optical system being diffraction limited, the optical system configured to form an image of the object at an image plane when the object is within the DOF and at a distance away from the optical system;an image sensor located at the image plane and adapted to form an electrical signal representative of the image as a raw image; a controller electrically connected to the image sensor and adapted to receive the electrical signal and perform image-processing on the raw image to form an enhanced image using an enhanced modulation transfer function (MTF) formed based on said object distance. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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Specification