Optical pattern recognition architecture implementing the mean- square error correlation algorithm

摘要

An optical architecture implementing the mean-square error correlation algorithm,PPMSE=&Sgr;[I-R].sup.2P Pfor discriminating the presence of a reference image R in an input image scene I by computing the mean-square-error between a time-varying reference image signal s.sub.1 (t) and a time-varying input image signal s.sub.2 (t) includes a laser diode light source which is temporally modulated by a double-sideband suppressed-carrier source modulation signal I.sub.1 (t) having the formPPI.sub.1 (t)=A.sub.1 [1+{square root}2m.sub.1 s.sub.1 (t)cos (2&pgr;f.sub.o t)]P Pand the modulated light output from the laser diode source is diffracted by an acousto-optic deflector. The resultant intensity of the + 1 diffracted order from the acousto-optic device is given by:P PI.sub.2 (t)=A.sub.2 [+2m.sub.2.sup.2 s.sub.2.sup.2 (t)-2{square root} 2m.sub.2 (t) cos (2&pgr;f.sub.o t]PPThe time integration of the two signals I.sub.1 (t) and I.sub.2 (t) on the CCD deflector plane produces the result R(&tgr;) of the mean-square error having the form: P PR(&tgr;)=A.sub.1 A.sub.2 {[T]+[2m.sub.2.sup.2·∫ s.sub.2. sup.2 (t-&tgr;)dt]-[2m.sub.1 m.sub.2 cos (2&tgr;f.sub.o &tgr;) ·. intg.s.sub.1 (t)s.sub.2 (t-&tgr;)dt]}PP where:P P s.sub.1 (t) is the signal input to the diode modulation source: PP s.sub.2 (t) is the signal input to the AOD modulation source;PP A.sub.1 is the light intensity;P PA.sub.2 is the diffraction efficiency; PPm.sub.1 and m.sub.2 are constants that determine the signal- to-bias ratio;P Pf.sub.o is the frequency offset between the oscillator at f.sub. c and the modulation at f.sub.c +f.sub.o ; andPP a.sub.o and a.sub.1 are constant chosen to bias the diode source and the acousto- optic deflector into their respective linear operating regions so that the diode source exhibits a linear intensity characteristic and the AOD exhibits a linear amplitude characteristic.