Second order derivative Use For Image Enhancement MCQ [Free PDF]

1. A filter is applied to an image whose response is independent of the direction of discontinuities in the image. The filter is/are ________

A. Isotropic filters
B. Box filters
C. Median filter
D. All of the mentioned

Answer: A

The isotropic filter is rotation invariant because it has the same response when applied to the image first and then after rotating the image.

2. In isotropic filtering, which of the following is/are the simplest isotropic derivative operator?

A. Laplacian
B. Gradient
C. All of the mentioned
D. None of the mentioned

Answer: A

An isotropic filtering is an example of a second-order derivative for enhancement and uses Laplacian as the simplest derivative operator, while gradient is used with first derivatives.

3. The Laplacian is which of the following operator?

A. Nonlinear operator
B. Order-Statistic operator
C. Linear operator
D. None of the mentioned

Answer: C

Derivatives of any order are linear operations and since Laplacian is the simplest isotropic derivative operator, so is a linear operator.
Order-Statistics operators are nonlinear operators.

4. A Laplacian for an image f(x, y) is defined as: is given by ________

A. [f(x + 1, y) + f(x – 1, y) – 2f(x, y)] and [f(x, y + 1) + f(x, y – 1) – 2f(x, y)] respectively
B. [f(x + 1, y + 1) + f(x, y – 1) – 2f(x, y)] and [f(x , y + 1) + f(x – 1, y) – 2f(x, y)] respectively
C. [f(x, y + 1) + f(x, y – 1) – 2f(x, y)] and [f(x + 1, y) + f(x – 1, y) – 2f(x, y)] respectively
D. None of the mentioned

Answer: A

For a Laplacian given by:∇2 f=
Applying second order derivative in x direction (∂2 f)/∂x2 = [f(x + 1, y) + f(x – 1, y) – 2f(x, y)], and
Applying second order derivative in y direction (∂2 f)/∂y2 = [f(x, y + 1) + f(x, y – 1) – 2f(x, y)].

5. The Laplacian ∇2 f=[f(x + 1, y) + f(x – 1, y) + f(x, y + 1) + f(x, y – 1) – 4f(x, y)], gives an isotropic result for rotations in increment by what degree?

A. 90o
B. 0o
C. 45o
D. None of the mentioned

Answer: A

The given Laplacian gives isotropic results for 90o incremental rotations.

6. The Laplacian incorporated with diagonal directions, i.e. ∇2 f=[f(x + 1, y) + f(x – 1, y) + f(x, y + 1) + f(x, y – 1) – 8f(x, y)], gives an isotropic result for rotations in increment by what degree?

A. 90o
B. 0o
C. 45o
D. None of the mentioned

Answer: A

The given Laplacian since includes the diagonal direction, so, gives an isotropic result for 45o incremental rotations.

7. Applying Laplacian has which of the following result(s)?

A. Produces images having greyish edge lines
B. Produces image having a featureless background
C. All of the mentioned
D. None of the mentioned

Answer: C

Since Laplacian is a derivative operator, so, highlights the gray-level discontinuities in an image and deemphasizes areas with slowly varying gray levels. Hence, produces images having greyish edge lines superimposed on the featureless background.

8. Applying Laplacian produces an image having featureless background which is recovered maintaining the sharpness of the Laplacian operation by either adding or subtracting it from the original image depending upon the Laplacian definition used. Which of the following is true based on the above statement?

A. If the definition used has a negative center coefficient, then subtraction is done
B. If the definition used has a positive center coefficient, then subtraction is done
C. If the definition used has a negative center coefficient, then the addition is done
D. None of the mentioned

Answer: A

Applying Laplacian produces an image having featureless background which is recovered maintaining the sharpness of the Laplacian operation using the original image either added if the Laplacian definition used has a positive center coefficient or subtracting the result from the original image if has a negative center coefficient.

9. A mask of size 3*3 is formed using Laplacian including diagonal neighbors that have a central coefficient of 9. Then, what would be the central coefficient of the same mask if it is made without diagonal neighbors?

A. 5
B. -5
C. 8
D. -8

Answer: A

The mask is formed by eliminating diagonal neighbors i.e. 4f(x, y) since each diagonal contains a -2f(x, y), the mask has 5 as its central coefficient.

10. Which of the following mask(s) is/are used to sharpen images by subtracting a blurred version of the original image from the original image itself?

A. Unsharp mask
B. High-boost filter
C. All of the mentioned
D. None of the mentioned

Answer: C

Unsharp mask sharpens images by subtracting a blurred version of the original image from the original image itself.
A high-boost filter is a generalized form of unsharp mask.

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