Improvements in or relating to Methods and Apparatus for Classifying Patterns

摘要

1,172,539. Pattern recognition. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 2 Oct., 1967 [12 Oct., 1966; 20 April, 1967], Nos. 45704/66 and 18324/67. Heading G4R. [Also in Division G2] Apparatus for pattern classification produces a diffraction image from the pattern, and electrical signals corresponding to the variation of illumination over at least a portion of the image, and performs a frequency analysis. Collimated light, e.g. from a laser and optics, is passed through a transparency (of a character, e.g. fingerprint, to be identified) or internally reflected at a face of a prism on which a finger is being held, and then focused by a lens to produce a diffraction pattern of the character which is focused on to a scanning disc having two co-linear radial slits with radial edges and which rotates relative to the character. A photomultiplier behind the scanning disc feeds the detected waveform for frequency analysis, followed by comparison of the resulting codes with stored codes, to identify the character. Alternatively a series of scanning discs can be used in turn, each having optical transmissivity which varies sinusoidal circumferentially, each disc having a different number of sine periods. This gives the frequency analysis directly. Instead of the circumferential scan above, a radial scan may be done using an annular slit of varying diameter, successive selection of a plurality of annular slits of different fixed diameters, or varying the magnification of the diffraction pattern image on a fixed annular slit. A combination of circumferential and radial scanning may be used. Fig. 8 shows the scanning disc 18 having two slits 19 referred to above superimposed on a second disc 20 with apertures 21. The two discs are rotated relative to each other, e.g both are rotated at slightly different speeds to scan successive annuli in turn. The scanning disc 18 may alternatively be superimposed on the disc shown in Fig. 9 which has different (prime) numbers of transparent and opaque regions in different annuli. The variation of transmissivity in each annulus could be sinusoidal rather than square-wave as shown in Fig. 9. Mechanical scanning as above may be replaced by a stationary plurality of concentric rings of photo-detectors, signals from different sectors and annuli of this array being added and subtracted in various combinations to obtain the amplitudes of various spatial frequencies.