Question

In terms of enhancement, what does mean and variance refers to?

(a) Average contrast and average gray level respectively

(b) Average gray level and average contrast respectively

(c) Average gray level in both

(d) Average contrast in both

This question was addressed to me in a job interview.

The doubt is from Histogram Specification and Use of Histogram Statistics for Image Enhancement topic in chapter Image Enhancement of Digital Image Processing

Answer 1

The correct option is (b) Average gray level and average contrast respectively

To elaborate: In terms of enhancement, mean refers to average gray level and variance to average contrast.

Given by, mean as: m = ∑_(i=0)^(L-1) ri p(ri ) and variance as: σ2(r) = ∑_(i=0)^(L-1) (ri –m)2 p(ri ).

Where, ri is histogram component of ith value of r, p(ri) is probability occurrence of gray level ri and L is the max gray value allowed.