Robert's operator is a non-linear filter to detect the presence of lines in an image. It work son a ecah 2x2 portion of the scence and is defined as the sum of the absolute differences between opposing corners:
G(x,y) = | f(x,y) − f(x+1,y-1) | + | f(x+1,y) − f(x,y-1) |$
Defined on page 251
Used on pages 251, 252, 253
Robert's operator: (i) G = |3−3|+|3−3| = |0|+|0| = 0 (ii) G = |7−2|+|3−8| = |5|+|−5| = 10 (iii) G = |5−6|+|7−1| = |−1|+|6| = 7 (iv) G = |7−8|+|1−2| = |−1|+|−1| = 2