Question

A contrast stretching result been obtained by setting (r1, s1) = (rmin, 0) and (r2, s2) = (rmax, L – 1), where, r and s are gray-values of image before and after processing respectively, L is the max gray value allowed and rmax and rmin are maximum and minimum gray-values in image respectively. What should we term the transformation function if r1 = r2 = m, some mean gray-value.

(a) Linear function

(b) Thresholding function

(c) Intermediate function

(d) None of the mentioned

I got this question in a national level competition.

My doubt stems from Piecewise-Linear Transformation Functions topic in section Intensity Transformations and Spatial Filtering of Digital Image Processing

Answer 1

The correct answer is (b) Thresholding function

Easy explanation: From (r1, s1) = (rmin, 0) and (r2, s2) = (rmax, L – 1), we have s1 = 0 and s2 = L – 1 and if r1 = r2 = m is set then the result becomes r1 = r2, s1 = 0 and s2 = L – 1, i.e. a thresholding function.