# Digital Image Processing Questions and Answers – Relationship between Pixels and Image Enhancement Basics

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This set of Digital Image Processing Multiple Choice Questions & Answers (MCQs) focuses on “Relationship between Pixels and Image Enhancement Basics”.

1. A pixel p at coordinates (x, y) has neighbors whose coordinates are given by:
(x+1, y), (x-1, y), (x, y+1), (x, y-1)
This set of pixels is called ____________
a) 4-neighbors of p
b) Diagonal neighbors
c) 8-neighbors
d) None of the mentioned

Explanation: The given set of neighbor pixel are 1 unit distance to right, left, up and below respectively from pixel p(x, y). So, are called 4-neighbors of p.

2. A pixel p at coordinates (x, y) has neighbors whose coordinates are given by:
(x+1, y+1), (x+1, y-1), (x-1, y+1), (x-1, y-1)
This set of pixels is called ____________
a) 4-neighbors of p
b) Diagonal neighbors
c) 8-neighbors
d) None of the mentioned

Explanation: The given set of neighbor pixel are 1 unit distance to right-up diagonal, right-down diagonal, left-up diagonal and left-down diagonal respectively from pixel p(x, y). So, are called Diagonal neighbors of p.

3. What is the set of pixels of 8-neighbors of pixel p at coordinates (x, y)?
a) (x+1, y), (x-1, y), (x, y+1), (x, y-1), (x+2, y), (x-2, y), (x, y+2), (x, y-2)
b) (x+1, y), (x-1, y), (x, y+1), (x, y-1), (x+1, y+1), (x+1, y-1), (x-1, y+1), (x-1, y-1)
c) (x+1, y+1), (x+1, y-1), (x-1, y+1), (x-1, y-1), (x+2, y+2), (x+2, y-2), (x-2, y+2), (x-2, y-2)
d) (x+2, y), (x-2, y), (x, y+2), (x, y-2), (x+2, y+2), (x+2, y-2), (x-2, y+2), (x-2, y-2)

Explanation: The set of pixels of 4-neighbors of p and Diagonal neighbors of p together are called as 8-neighbors of pixel p(x, y).

4. Two pixels p and q having gray values from V, the set of gray-level values used to define adjacency, are m-adjacent if:
a) q is in N4(p)
b) q is in ND(p) and the set N4(p) ∩ N4(q) has no pixels whose values are from V
c) Any of the mentioned
d) None of the mentioned

The above conditioned Two pixels p and q are m-adjacent if:
q is in N4(p), or
q is in ND(p) and the set N4(p) ∩ N4(q) has no pixels whose values are from V.

5. Let S, a subset of pixels in an image, is said to be a connected set if:
a) If for any pixel p in S, the set of pixels that are connected to it in Sis only one
b) If it only has one connected component
c) If S is a region
d) All of the mentioned

Explanation: For a subset of pixels in an image S
For any pixel p in S, the set of pixels is called a connected component of S if connected to p in S. The set S is called a connected set if it only has one connected component.
S, is a region of the image if S is a connected set.

6. Let R be a subset of pixels in an image. How can we define the contour of R?
a) If R is a region, and the set of pixels in R have one or more neighbors that are not in R
b) If R is an entire image, then the set of pixels in the first and last rows and columns of R
c) All of the mentioned
d) None of the mentioned

Explanation: For a subset of pixels in an image R
The boundary or contour of a region R is the set of pixels in the region that have one or more neighbors that are not in R.
In case R is an entire image, then its boundary is defined as the set of pixels in the first and last rows and columns of the image.

7. For pixels p(x, y), q(s, t), and z(v, w), D is a distance function or metric if:
a) D(p, q) ≥ 0
b) D(p, q) = D(q, p)
c) D(p, z) ≤ D(p, q) + D(q, z)
d) All of the mentioned

Explanation: For pixels p(x, y), q(s, t), and z(v, w), D is a distance function or metric if:
(i) D(p, q) ≥ 0, (D(p, q) = 0 if p=q),
(ii) D(p, q) = D(q, p), and
(iii) D(p, z) ≤ D(p, q) + D(q, z).

8. For pixels p(x, y), q(s, t), the Euclidean distance between p and q is defined as:
a) D(p, q) = [(x – s)2 + (y – t)2]1/2
b) D(p, q) = |x – s| + |y – t|
c) D(p, q) = max (|x – s| + |y – t|)
d) None of the mentioned

Explanation: The Euclidean distance for pixels p(x, y), q(s, t) is:
D(p, q) = [(x – s)2 + (y – t)2]1/2.

9. For pixels p(x, y), q(s, t), the city-block distance between p and q is defined as:
a) D(p, q) = [(x – s)2 + (y – t)2]1/2
b) D(p, q) = |x – s| + |y – t|
c) D(p, q) = max (|x – s| + |y – t|)
d) None of the mentioned

Explanation: The city-block distance for pixels p(x, y), q(s, t) is the D4 distance given by:
D(p, q) = |x – s| + |y – t|.

10. For pixels p(x, y), q(s, t), the chessboard distance between p and q is defined as:
a) D(p, q) = [(x – s)2 + (y – t)2]1/2
b) D(p, q) = |x – s| + |y – t|
c) D(p, q) = max (|x – s| + |y – t|)
d) None of the mentioned

Explanation: The chessboard distance for pixels p(x, y), q(s, t) is the D8 distance given by:
D(p, q) = max (|x – s| + |y – t|).

11. The domain that refers to image plane itself and the domain that refers to Fourier transform of an image is/are :
a) Spatial domain in both
b) Frequency domain in both
c) Spatial domain and Frequency domain respectively
d) Frequency domain and Spatial domain respectively

Explanation: Spatial domain itself refers to the image plane, and approaches in this category are based on direct manipulation of pixels in an image.
Techniques based on Frequency domain processing are based on modifying the Fourier transform of an image.

12. What is the technique for a gray-level transformation function called, if the transformation would be to produce an image of higher contrast than the original by darkening the levels below some gray-level m and brightening the levels above m in the original image.
a) Contouring
b) Contrast stretching
d) Point processing

Explanation: For a gray-level transformation function “s=T(r)”, where r and s are the gray-level of f(x, y) (input image) and g(x, y) (output image) respectively at any point (x, y).
Then the technique, contrast stretching compresses the value of r below m by transformation function into a narrow range of s, towards black and brightens the value of r above m.

13. For Image Enhancement a general-approach is to use a function of values of f (input image) in a predefined neighborhood of (x, y) to determine the value of g (output image) at (x, y). The techniques that uses such approaches are called ________
a) Contouring
b) Contrast stretching
d) None of the mentioned

Explanation: The above mentioned approach is based on the use of masks. A mask is a small m*n 2-D array in which the values of mask coefficients determine the nature of the process and Image Enhancement on such is called Mask Processing or Filtering. 