1. Which of the following is the primary objective of sharpening an image?

A. Blurring the image
B. Highlight fine details in the image
C. Increase the brightness of the image
D. Decrease the brightness of the image

Answer: B

The sharpening of the image helps in highlighting the fine details that are present in the image or to enhance the details that are blurred due to some reason like adding noise.

2. Image sharpening process is used in electronic printing.

A. True
B. False

Answer: A

The applications of image sharpening are present in various fields like electronic printing, autonomous guidance in military systems, medical imaging, and industrial inspection.

3. In the spatial domain, which of the following operation is done on the pixels in sharpening the image?

A. Integration
B. Average
C. Median
D. Differentiation

Answer: D

We know that, in blurring the image, we perform the average of pixels which can be considered as integration. As sharpening is the opposite process of blurring, logically we can tell that we perform differentiation on the pixels to sharpen the image.

4. Image differentiation enhances the edges, and discontinuities and deemphasizes the pixels with slow varying gray levels.

A. True
B. False

Answer: A

Fundamentally, the strength of the response of the derivative operative is proportional to the degree of discontinuity in the image. So, we can state that image differentiation enhances the edges, and discontinuities and deemphasizes the pixels with slow varying gray levels.

5. In which of the following cases, we wouldn’t worry about the behavior of the sharpening filter?

A. Flat segments
B. Step discontinuities
C. Ramp discontinuities
D. Slow varying gray values

Answer: D

We are interested in the behavior of derivatives used in sharpening in the constant gray level areas i.e., flat segments, and at the onset and end of discontinuities, i.e., step and ramp discontinuities.

6. Which of the following is the valid response when we apply the 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

Answer: C

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

7. Which of the following is not a valid response when we apply a second derivative?

A. Zero response at the onset of gray level step
B. Nonzero response at the onset of gray level step
C. Zero response at flat segments
D. Nonzero response along the ramps

Answer: B

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

8. If f(x,y) is an image function of two variables, then the first order derivative of a one dimensional function, f(x) is:

A. f(x+1)-f(x)
B. f(x)-f(x+1)
C. f(x-1)-f(x+1)
D. f(x)+f(x-1)

Answer: A

The first order derivative of a single dimensional function f(x) is the difference between f(x) and f(x+1).

That is, ∂f/∂x=f(x+1)-f(x).

9. Isolated point is also called a noise point.

A. True
B. False

Answer: A

The point which has a very high or very low gray-level value compared to its neighbors, then that point is called an isolated point or noise point. The noise point is of one-pixel size.

10. What is the thickness of the edges produced by first-order derivatives when compared to that of second-order derivatives?

A. Finer
B. Equal
C. Thicker
D. Independent

Answer: C

We know that the first-order derivative is nonzero along the entire ramp while the second order is zero along the ramp. So, we can conclude that the first-order derivatives produce thicker edges and the second-order derivatives produce much finer edges.