Question

Which of the facts(s) is/are true for the first order derivative of a digital function?

(a) Must be nonzero in the areas of constant grey values

(b) Must be zero at the onset of a gray-level step or ramp discontinuities

(c) Must be nonzero along the gray-level ramps

(d) None of the mentioned

I have been asked this question in semester exam.

My doubt is from Sharpening Spatial Filters-2 topic in section Intensity Transformations and Spatial Filtering of Digital Image Processing

Answer 1

The correct choice is (c) Must be nonzero along the gray-level ramps

The explanation: The first order derivative of a digital function is defined as:

 Must be zero in the areas of constant grey values.

 Must be nonzero at the onset of a gray-level step or ramp discontinuities.

 Must be nonzero along the gray-level ramps.