GB1399675A - Method and apparatus for fingerprint identification - Google Patents

Abstract

1399675 Fingerprint recognition systems SPERRY RAND CORP 9 Oct 1973 46963/73 Heading G4R An optical processor for use in fingerprint identification determines the angular direction of the ridge lines at each of a number of spaced small areas of the print. The principle of operation is illustrated by Fig. 1. The fingerprint is, in this embodiment, a transparency occupying the field 10<SP>1</SP>. Coherent light is directed through the transparency and forms a fourier transform at the focus of lens 13. The transform consists of an undiffracted central spot surrounded by an annular band formed by the lobes of the diffracted components. For example, any small area of the print having vertical ridges will provide two diffraction lobes 12d, 12d<SP>1</SP> on a horizontal axis irrespective of the position of the area within the print. A rotating mask 19 is placed in the transform plane. It is opaque except for slit 19<SP>1</SP>. Light passing through the slit is directed by lens 18 to photosensors 16a, 16b,..., each of which can receive light from only a corresponding area 12a, 12b, ... of the print. For example, sensor 16d will receive light from area 12d, but only when slit 19<SP>1</SP> is aligned with either of diffraction lobes 12d<SP>1</SP>. Mask 19 has peripheral timing slots (not shown) which increment a counter such that the counter output is indicative of the instantaneous angular orientation of the slot. When a photosensor provides an output pulse the present count is read in to an associated register so that at the end of a half revolution of the mask, each register will contain an indication of the orientation of the ridge lines at the corresponding small area of the print and may be used for identification purposes. In an alternative arrangement, Fig. 4, a live finger F is used. Coherent light directed on to the finger forms a fourier transform at 32. The transform is imaged on to a rotating mirror 33 which has an opaque bar across its diameter. The light intensity at a photosensor 34 of an array of sensors will therefore fall when the orientation of the bar is perpendicular to the ridge lines at the corresponding small area of the fingerprint and is used to read a count in to a register as described above. Reference is made to the use of a sawtooth generator instead of the incrementing counter, to the use of an oscillating mirror to compensate for off-centring of the print, and to serial rather than parallel operation.