# Digital Image Processing Questions and Answers – Piecewise-Linear Transformation Functions

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This set of Digital Image Processing Multiple Choice Questions & Answers (MCQs) focuses on “Piecewise-Linear Transformation Functions”.

1. Which gray-level transformation increase the dynamic range of gray-level in the image?
a) Power-law transformations
b) Negative transformations
c) Contrast stretching
d) None of the mentioned

Explanation: Increasing the dynamic range of gray-levels in the image is the basic idea behind contrast stretching.

2. When is the contrast stretching transformation a linear function, for r and s as gray-value of image before and after processing respectively?
a) r1 = s1 and r2 = s2
b) r1 = r2, s1 = 0 and s2 = L – 1, L is the max gray value allowed
c) r1 = 1 and r2 = 0
d) None of the mentioned

Explanation: If r1 = s1 and r2 = s2 the contrast stretching transformation is a linear function.

3. When is the contrast stretching transformation a thresholding function, for r and s as gray-value of image before and after processing respectively?
a) r1 = s1 and r2 = s2
b) r1 = r2, s1 = 0 and s2 = L – 1, L is the max gray value allowed
c) r1 = 1 and r2 = 0
d) None of the mentioned

Explanation: If r1 = r2, s1 = 0 and s2 = L – 1, the contrast stretching transformation is a thresholding function.
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4. What condition prevents the intensity artifacts to be created while processing with contrast stretching, if r and s are gray-values of image before and after processing respectively?
a) r1 = s1 and r2 = s2
b) r1 = r2, s1 = 0 and s2 = L – 1, L is the max gray value allowed
c) r1 = 1 and r2 = 0
d) r1 ≤ r2 and s1 ≤ s2

Explanation: While processing through contrast stretching, if r1 ≤ r2 and s1 ≤ s2 is maintained, the function remains single valued and so monotonically increasing. This helps in the prevention of creation of intensity artifacts.

5. A contrast stretching result been obtained by setting (r1, s1) = (rmin, 0) and (r2, s2) = (rmax, L – 1), where, r and s are gray-values of image before and after processing respectively, L is the max gray value allowed and rmax and rmin are maximum and minimum gray-values in image respectively. What should we term the transformation function if r1 = r2 = m, some mean gray-value.
a) Linear function
b) Thresholding function
c) Intermediate function
d) None of the mentioned

Explanation: From (r1, s1) = (rmin, 0) and (r2, s2) = (rmax, L – 1), we have s1 = 0 and s2 = L – 1 and if r1 = r2 = m is set then the result becomes r1 = r2, s1 = 0 and s2 = L – 1, i.e. a thresholding function.

6. A specific range of gray-levels highlighting is the basic idea of __________
a) Contrast stretching
b) Bit –plane slicing
c) Thresholding
d) Gray-level slicing

Explanation: gray-level slicing is being done by two approach: One approach is to give all gray level of a specific range high value and a low value to all other gray levels.
Second approach is to brighten the pixels gray-value of interest and preserve the background.
I.e. in both highlighting of a specific range of gray-level is been done.

7. What is/are the approach(s) of the gray-level slicing?
a) To give all gray level of a specific range high value and a low value to all other gray levels
b) To brighten the pixels gray-value of interest and preserve the background
c) All of the mentioned
d) None of the mentioned

Explanation: There are basically two approach of gray-level slicing:
One approach is to give all gray level of a specific range high value and a low value to all other gray levels.
Second approach is to brighten the pixels gray-value of interest and preserve the background.

8. Which of the following transform produces a binary image after processing?
a) Contrast stretching
b) Gray-level slicing
c) All of the mentioned
d) None of the mentioned

Explanation: The approach of gray-level slicing “to give all gray level of a specific range high value and a low value to all other gray levels” produces a binary image.
One of the transformation in Contrast stretching darkens the value of r (input image gray-level) below m (some predefined gray-value) and brightens the value of r above m, giving a binary image as result.

9. Specific bit contribution in the image highlighting is the basic idea of __________
a) Contrast stretching
b) Bit –plane slicing
c) Thresholding
d) Gray-level slicing

Explanation: Bit-plane slicing highlights the contribution of specific bits made to total image, instead of highlighting a specific gray-level range.

10. In bit-plane slicing if an image is represented by 8 bits and is composed of eight 1-bit plane, with plane 0 showing least significant bit and plane 7 showing most significant bit. Then, which plane(s) contain the majority of visually significant data.
a) Plane 4, 5, 6, 7
b) Plane 0, 1, 2, 3
c) Plane 0
d) Plane 2, 3, 4, 5

Explanation: In bit-plane slicing, for the given data, the higher-ordered bits (mostly top four) contains most of the data visually signified.

11. Which of the following helps to obtain the number of bits to be used to quantize each pixel.
a) Gray-level slicing
b) Contrast stretching
c) Contouring
d) Bit-plane slicing

Explanation: Bits-plane slicing helps in obtaining the importance played by each bit in the image by separating the image into bit-planes.

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