Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2002-07-24
2004-10-19
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S208100, C382S124000
Reexamination Certificate
active
06806483
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-228972, filed Jul. 30, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensor system having a photosensor array constituted by two-dimensionally arraying a plurality of photosensors, and an image reading method using the photosensor system.
2. Description of the Related Art
In recent years, individual identification techniques have actively been studied to strengthen the security function in access to a confidential document stored in a computer, e-commerce on a network, and entrance/exit to/from an important facility. The individual identification method uses, e.g., biometric information. In particular, fingerprints are different between individuals, do not change as long as a person lives, and thus are utilized as an important feature which realizes individual identification. From this, fingerprint collation apparatuses have enthusiastically been developed.
This fingerprint collation apparatus requires a two-dimensional image reading apparatus which uses a finger as an object to be sensed and reads a fine three-dimensional structure on the object surface. An example of the two-dimensional image reading apparatus is a photosensor system which comprises a photosensor array constituted by arraying photoelectric conversion elements (photosensors) in a two-dimensional matrix and reads a fingerprint image by the photosensor array. A known photosensor system of this type uses a transmission photosensor as a photoelectric conversion element and has an illumination light source attached to the back surface. A schematic arrangement of the photosensor system is shown in
FIGS. 13
,
14
A, and
14
B.
This photosensor system schematically comprises a photosensor array
101
and an illumination light source (back light) BL. In the photosensor array
101
, a plurality of photosensors
10
are arrayed in a two-dimensional matrix on one surface of a glass board GB, and a light-receiving surface
102
is formed by covering the photosensor array with a transparent insulating film
20
. The light source BL is arranged on the back side of the photosensor array
101
opposite to the side of the light-receiving surface
102
. As the photosensor
10
, e.g., a CCD is used. The photosensors
10
arrayed in a matrix are scanned and driven by horizontal and vertical scanning circuits (not shown). The number of electron-hole pairs (charge amount) generated in correspondence with the quantity of light incident on the light-receiving portions of the photosensors is detected to sense the luminance of received light.
To read a fingerprint image by the photosensor system, a finger is set on the light-receiving surface
102
and irradiated with light from the light source BL attached to the back surface of the photosensor array_-
101
. Light emitted by the light source BL irradiates the finger surface through transparent insulating film portions except the formation regions of the photosensors
10
. The light is scattered and reflected in accordance with a three-dimensional structure corresponding to the fingerprint of the finger in contact with the light-receiving surface
102
. Then, reflected light with a bright/dark pattern corresponding to the fingerprint enters the photosensor array
101
.
When the finger touches the light-receiving surface
102
, the ridge portions (projecting portions) of the fingerprint tightly contact the light-receiving surface
102
, and strongly scatter and reflect irradiation light from the light source BL. A large quantity of light enters the photosensor
10
, and the ridge portions are detected bright (white). The valley portions (recessed portions) of the fingerprint do not tightly contact the light-receiving surface
102
, and irradiation light from the light source BL is weakly scattered at the interface between the transparent insulating film
20
and air. A small quantity of light enters the photosensor
10
, and the valley portions are detected dark (black). The bright/dark pattern corresponding to three-dimensional structure of the fingerprint is two-dimensionally read to read the fingerprint image.
The state of the finger surface, i.e., the state of the skin surface of a person changes due to the individual difference in the secretion of sebum or the moisture retention of the skin. The skin surface state also varies depending on the ambient humidity, air temperature, or the like. The skin surface is finely corrugated, and even the surface of the ridge portion of the fingerprint is subtly corrugated.
FIG. 14A
is an enlarged view showing the main part when the skin surface of the finger is moist with a proper amount of sebum or water at the fingerprint reading portion of the photosensor system.
FIG. 14B
is an enlarged view showing the main part when the skin surface of the finger is dry due to a shortage of sebum or water.
If the finger has a properly moistened skin, as shown in
FIG. 14A
, the ridge portions can tightly contact the light-receiving surface
102
via sebum, water, or the like. The entire ridge portions strongly scatter and reflect irradiation light, and the ridge and valley portions can be clearly read to accurately read the fingerprint image.
To the contrary, if the finger skin is dry, as shown in
FIG. 14B
, the skin surfaces at the ridge portions are finely corrugated, which make it difficult to tightly contact the light-receiving surface
102
. The projecting portions of the ridge portions tightly contact the photosensor
10
, strongly scatter and reflect irradiation light, and are detected bright (white). The recessed portions of the ridge portions do not tightly contact the light-receiving surface and are detected dark (black). In other words, even the ridge portion is detected bright (white) and dark (black) in different parts. As a result, the ridge portion becomes unclear, failing to accurately read the fingerprint image.
BRIEF SUMMARY OF THE INVENTION
The present invention has an advantage that a photosensor system which has a photosensor array constituted by two-dimensionally arraying a plurality of photosensors, uses the fingerprint of a finger as a finger to be sensed, and reads a fingerprint image can clearly read the fingerprint image of even a dry finger, and can read a fingerprint image with a uniform contrast without any contrast nonuniformity generated in the fingerprint image.
The present invention also has an advantage that the power consumption of an illumination light source used can be reduced in reading a fingerprint image.
To achieve the above advantages, a photosensor system according to the present invention comprises a photosensor array which is constituted by two-dimensionally arraying a plurality of photosensors and has a light-receiving surface, a first light source (front light) which is arranged to face the light-receiving surface, and illuminates a rear surface of a finger set on the light-receiving surface, and image reading section which reads a fingerprint image by receiving light that is emitted by the first light source and passes through the finger.
The image reading section in the present invention comprises sensitivity adjustment reading section which reads the fingerprint image at a plurality of image reading sensitivities, optimal image reading sensitivity deriving section which derives an optimal image reading sensitivity suitable for reading operation of the fingerprint image on the basis of fingerprint images read by the sensitivity adjustment reading section at the image reading sensitivities, and image reading sensitivity setting section which sets the optimal image reading sensitivity as an image reading sensitivity. The optimal image reading sensitivity deriving section extracts maximum and minimum values for each image reading sensitivity out of pixel data based on an image pattern of the read fingerprint image, calculates a da
Aoki Hisashi
Iihama Tomomi
Mizutani Yasushi
Nakamura Yoshiaki
Sasaki Makoto
Casio Computer Co. Ltd.
Frishauf Holtz Goodman & Chick P.C.
Luu Thanh X.
Sohn Seung C.
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