Page 392 - Introduction to Information Optics

7.3. Polychromatic Pattern Recognition

S r{a,/3) O
S g(a,j8) E3

Stop
Band

Fig. 7.22. Multicolor Fourier-domain filtering, // r , W ff , and H h are red, green, and blue color-
matched spatial filters.

street scene (in gray level) is shown in Fig. 7.23a. Figure 7.23b shows the
polychromatic detection, in which a blue correlation spot representing the
location of the blue van and a red spot representing the stop sign are observed.

7.3.2. DETECTION WITH SPATIAL-DOMAIN FILTERS

Liquid crystal-TV (LCTV) has been widely used in optical processing. By
exploiting the inherent polychromatic structure of the LCTV pixels, polychro-
matic target detection can be developed in a JTC. The LCTV we consider is a
color LCTV (Seiko Model LVD-202) with 6 lines/mm resolution, which can
be used as the spatial-carrier frequency. The enlarged liquid crystal-pixel array
is shown in Fig. 7.24a. If the LCTV panel is illuminated by coherent red, blue,
and green light, the dispersed spectral distribution at the Fourier domain is
shown in Fig. 7.24b. For simplicity, let us consider a red reference signal
f r(x, >'), with blue, green, and red object images displayed on the LCTV panel,
as written by

*(x, v) = / P(x, y + c; A r) + f r(x, y - c; A,) + /„(*, y -d; A h) + / ff(x, y-e; A,),

(7.19)