
6.2 Gray Scale Modification
223
in Figs.
5a-5f,
respectively. In Fig. 6, each black point has had its gray level
decremented, and each white point has had its level incremented, by a random
amount ζ in the range 0 ^ ζ ^ 9(b
—
w), where b = black, w = white, and
θ = 0.1,0.2,..., 0.9,1 in Figs.
6a-6j,
respectively. A method of removing salt-
and-pepper noise is described in Section
6.4.1.
Noise may depend not only on the gray level of the picture at the given
point, but also on the levels at nearby points. This is so for many of the examples
previously mentioned—e.g., for the flying-spot scanner, since the spot size is
finite; and for photographi ...