With reference to Eq. (10.3-20), advance an argument that establishes that 0 ≤η(k)≤ 1, for...

With reference to Eq. (10.3-20), advance an argument that establishes that 0 ≤η(k)≤ 1, for k in the range 0 ≤ k ≤ L − 1, where the minimum is achievable only by images with constant intensity, and the maximum occurs only for 2-valued images with values 0 and L − 1.

(10.3-20)