Question

Subtracting Laplacian from an image is proportional to which of the following?

(a) Unsharp masking

(b) Box filter

(c) Median filter

(d) None of the mentioned

This question was addressed to me in my homework.

My question is taken from Use of First Order Derivative for Enhancement topic in section Image Enhancement of Digital Image Processing

Answer 1

Right option is (a) Unsharp masking

For explanation I would say: subtracting Laplacian from an image gives:

f(x,y)- ∇^2 f(x,y) = f(x, y) – [f(x + 1, y) + f(x – 1, y) + f(x, y + 1) + f(x, y – 1) – 4f(x, y)]

That on calculation gives 5[1.2 f(x, y) – f ̅(x, y)] ≈ 5[f(x, y) – f(x, y)]

Where f(x, y) – f(x, y) is the unsharp masking definition.