Image Enhancement MCQ

1. The principal factor to determine the spatial resolution of an image is _______

A. Quantization
B. Sampling
C. Contrast
D. Dynamic range

Answer: B

The spatial resolution of an image is principally determined by Sampling.

2. What causes the effect, imperceptible set of the very fine ridge-like structures in areas of smooth gray levels?

A. Caused by the use of an insufficient number of gray levels in smooth areas of a digital image
B. Caused by the use of a huge number of gray levels in smooth areas of a digital image
C. All of Mentioned
D. None of the mentioned

Answer: A

The set of the very fine ridge-like structures in the area of smooth gray levels generally is quite visible in images displayed using 16 or less uniformly spaced gray levels.

3. What is the name of the effect caused by the use of an insufficient number of gray levels in smooth areas of a digital image?

A. Dynamic range
B. Ridging
C. Graininess
D. False contouring

Answer: D

The effect caused due to an insufficient number of gray levels in smooth areas of a digital image is called false contouring, so-called because the ridges resemble topographic contours on a map.

4. Using a rough rule of thumb, and assuming powers of 2 for convenience, what image size is about the smallest images that can be expected to be reasonably free of objectionable sampling checkerboards and false contouring?

A. 512*512pixels and 16 gray levels
B. 256*256pixels and 64 gray levels
C. 64*64pixels and 16 gray levels
D. 32*32pixels and 32 gray levels

Answer: B

An image of 128*128pixels shows a pronounced checkerboard pattern, while for a 256*256pixels image a minimum gray level of 64 is required to remove false contouring.
Also, the effect is quite visible in images displayed using 16 or less uniformly spaced gray levels.

5. What does a shift up and right in the curves of isopreference curve simply means? Verify-in terms of N (number of pixels) and k (L=2k, L is the gray level) values.

A. Smaller values for N and k, implies a better picture quality
B. Larger values for N and k, imply low picture quality
C. Larger values for N and k, imply better picture quality
D. Smaller values for N and k, imply low picture quality

Answer: C

Points lying on an isopreference curve correspond to images of equal subjective quality. It was found that the isopreference curves tended to shift right and upward with the details of the image. So, a shift up and right in the curves simply means larger values for N and k, implying better picture quality.

6. How do the curves behave to the detail in the image in isopreference curve?

A. Curves tend to become more vertical as the detail in the image decreases
B. Curves tend to become less vertical as the detail in the image increases
C. Curves tend to become less vertical as the detail in the image decreases
D. Curves tend to become more vertical as the detail in the image increases

Answer: D

The curves in isopreference curve tend to become more vertical as the detail in the image increases.
The right side graph shows the same, the curve for a crowd is nearly vertical.

7. For an image with a large amount of detail, if the value of N (number of pixels) is fixed then what is the gray level dependency in the perceived quality of this type of image?

A. independent of the number of gray levels used
B. Nearly independent of the number of gray levels used
C. Highly dependent on the number of gray levels used
D. None of the mentioned

Answer: B

For images with high details of the image, only a few gray levels may be needed.

8. What is a band-limited function?
A. A function of limited duration whose highest frequency is finite
B. A function of limited duration whose highest frequency is infinite
C. All of Mentioned
D. None of the mentioned

Answer: A

Functions whose area under the curve is finite can be represented in terms of sines and cosines of various frequencies. The highest frequency is determined by the sine/cosine component is the highest “frequency content” of the function. If this highest frequency is finite and the function is of unlimited duration, then, these functions are called band-limited functions.

9. For a band-limited function, which Theorem says that “if the function is sampled at a rate equal to or greater than twice its highest frequency, the original function can be recovered from its samples”?

A. Band-limitation theorem
B. Aliasing frequency theorem
C. Shannon sampling theorem
D. None of the mentioned

Answer: C

For a band-limited function, the Shannon sampling theorem says that “if the function is sampled at a rate equal to or greater than twice its highest frequency, the original function can be recovered from its samples”.

10. What is the name of the phenomenon that corrupts the sampled image, and how does it happen?

A. Shannon sampling, if the band-limited functions are undersampled
B. Shannon sampling, if the band-limited functions are oversampled
C. Aliasing if the band-limited functions are undersampled
D. Aliasing, if the band-limited functions are oversampled

Answer: C

If the band-limited functions are undersampled, then a phenomenon called aliasing corrupts the sampled image.

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Image Enhancement MCQ

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