Liquid platen fingerprint image enhancement
First Claim
1. An optical fingerprint imaging system comprising in combination:
- a platen having a finger-touching surface to which a liquid layer may be applied;
means for providing two interrogating light beams, one on each side of and below the finger position on the platen and positioned to illuminate and provide a modulated light beam from the ridges and valleys of the finger surface when immersed in the liquid layer and placed on the finger-touching surface of the platen;
the two interrogating light beams each being collimated and the projections of each beam into a horizontal plane assuming an angle of approximately forty-five degrees with the longitudinal axis of the finger when place on the finger-touching surface;
imaging means;
a mirror for reflecting the visible modulated light beam from the finger ridges and valleys to the imaging means; and
,a first polarizing filter positioned between the platen and the mirror to intercept the visible modulated light prior to reflection from the mirror.
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Accused Products
Abstract
A fingerprint enhancement system has a platen with a liquid contacting and finger-touching surface. Two collimated interrogating light beams lie below and are opposite sides of the finger-touching surface. The horizontal extensions of the light beams assume an angle of approximately forty-five degrees with the finger longitudinal axis. Side surfaces of the platen are oriented normal to the incident colliminated light beams prior to interrogation. The light beam modulated by the fingerprint passes to a reflecting mirror, imaging means and a scanner below the platen. A polarizing filter lies between the platen and reflecting mirror. A second polarizing filter lies above the platen. A contrast enhancement circuit increases the modulation of the scanned fingerprint signal and automatically adjusts the level of the modulated signal without saturation. Circuit filtering eliminates spurious input signals. Finger position sensing by a light emitting diode and photo transistor is also provided.
76 Citations
16 Claims
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1. An optical fingerprint imaging system comprising in combination:
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a platen having a finger-touching surface to which a liquid layer may be applied; means for providing two interrogating light beams, one on each side of and below the finger position on the platen and positioned to illuminate and provide a modulated light beam from the ridges and valleys of the finger surface when immersed in the liquid layer and placed on the finger-touching surface of the platen; the two interrogating light beams each being collimated and the projections of each beam into a horizontal plane assuming an angle of approximately forty-five degrees with the longitudinal axis of the finger when place on the finger-touching surface; imaging means; a mirror for reflecting the visible modulated light beam from the finger ridges and valleys to the imaging means; and
,a first polarizing filter positioned between the platen and the mirror to intercept the visible modulated light prior to reflection from the mirror. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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- 11. A method of fingerprint imaging comprising immersing the finger in a layer of liquid on a finger-touching surface, the layer of liquid being of sufficient thickness to immerse the ridges and at least a portion of the valleys of the finger surface, interrogating the finger surface by two colliminated light beams from below and respectively on opposite sides of the finger surface, the horizontal projection of the collimated light beams assuming an angle of approximately forty-five degrees with the longitudinal axis of the finger when placed on the finger-touching surface, intercepting and optically filtering by a polarizing filter the modulated light reflected from the finger surface, and thereafter reflecting and scanning the modulated light.
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14. A fingerprint imaging system comprising in combination:
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a platen having a finger-touching surface to which a liquid layer may be applied; means for providing two collimated interrogating light beams to illuminate and provide a modulated light beam from the ridges and valleys of a finger surface immersed in the liquid layer and placed on the finger-touching surface; means to image the modulated light beam; a circuit to enhance the contrast of the imaged light beam; electrical and optical filtering means; said contrast enhancement circuit including the electrical filter means to filter out spurious input signals; said optical filtering means comprising a polarizing filter positioned on one side of the platen to intercept the modulated light beam prior to its being imaged. - View Dependent Claims (15, 16)
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Specification