Question

Which of the following is the valid response when we apply a first derivative?

(a) Non-zero at flat segments

(b) Zero at the onset of gray level step

(c) Zero in flat segments

(d) Zero along ramps

This question was posed to me in an online interview.

My question is from Sharpening Spatial Filters topic in division Intensity Transformations and Spatial Filtering of Digital Image Processing

Answer 1

Right option is (c) Zero in flat segments

To elaborate: The derivations of digital functions are defined in terms of differences. The definition we use for first derivative should be zero in flat segments, nonzero at the onset of a gray level step or ramp and nonzero along the ramps.