GB1188302A - Improvements relating to Fingerprint Identification - Google Patents

Abstract

1,188,302. Recognizing finger-prints. BRITISH AIRCRAFT CORP Ltd. 24 July, 1967 [27 July, 1966], No. 33740/66. Heading G4R. [Also in Division G2] In finger-print identification apparatus, known finger-prints in an array are correlated optically with the Fourier transform of an unknown print to produce light spots each with an intensity depending on the correlation between the unknown print and a known print, the co-ordinates in the array of a known print producing a spot exceeding a predetermined intensity being read out. Coherent light from a laser source is transmitted through a slide holding an array of known finger-prints, and then a Fourier-transforming lens, on to a hologram of the unknown print, a reference beam split from the original laser light also being directed on to the hologram. The hologram output light is imaged by an optical correlator on to a vidicon which scans the correlation light spots. The correlator or the array of known prints is rotatable to allow for non-standard orientation of the unknown print or print fragment. The amplitudes of the spots are digitized and fed with the values of their position co-ordinates to a computer which stores the data for spots of above a certain amplitude for subsequent print-out. A plurality of scans could be made with successively larger or smaller thresholds until a suitable number of spots above the threshold is found. The scanning could be done using masks movable in the X and Y directions over the slide of known prints. A series of slides of known prints can be tried in turn automatically until a match is found. By using the technique of volume holography, a plurality of arrays of known prints can be stored on a single slide, the slide being rotated to access successive arrays. The distance between the Fourier-transforming lens and the hologram of the unknown print may be varied to compensate for different sizes of unknown print. The hologram is formed by replacing the slide of known prints by a transparency of the unknown print and putting a photographic plate where the hologram will eventually go for print identification. The reference beam could be dispensed with throughout in which case a mere Fourier transform of the unknown print is produced and used instead of a hologram. The reference beam, when used, also has the function of normalizing the output against changes in source brightness.