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2.8, Processing with Incoherent Light
(b)
Fig. 2.49. Color image subtration. (a) Input (color) images, (b) Subtrated (color) image,
transparency. To avoid the output moire fringe pattern, we sample the primary
color images in orthogonal directions as given by
T(x,y) = K{T r(x,y)[l + sgn(coseo r>')] sgn(cosro fcx)]
)D + sgn(coso; ff.Y)]}
where K is a proportionality constant; T r, T h, and T g are the red, blue, and
green color image exposures; oj r, oj h, and io g are the respective carrier spatial
frequencies: y is the film gamma; and
sgn(cos x) 0, cos x — 0,
1, cos x < 0.
Notice that the diffraction efficiency can be improved by bleaching the encoded
transparency. Nevertheless, if we insert the encoded transparency at the input
