# Digital Image Processing Questions And Answers – Basic Intensity Transformation Functions

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This set of Digital Image Processing Interview Questions and Answers focuses on “Basic Intensity Transformation Functions”.

1. Which of the following expression is used to denote spatial domain process?
a) g(x,y)=T[f(x,y)]
b) f(x+y)=T[g(x+y)]
c) g(xy)=T[f(xy)]
d) g(x-y)=T[f(x-y)]

Explanation: Spatial domain processes will be denoted by the expression g(x,y)=T[f(x,y)], where f(x,y) is the input image, g(x,y) is the processed image, and T is an operator on f, defined over some neighborhood of (x, y). In addition, T can operate on a set of input images, such as performing the pixel-by-pixel sum of K images for noise reduction.

2. Which of the following shows three basic types of functions used frequently for image enhancement?
a) Linear, logarithmic and inverse law
b) Power law, logarithmic and inverse law
c) Linear, logarithmic and power law
d) Linear, exponential and inverse law

Explanation: In introduction to gray-level transformations, which shows three basic types of functions used frequently for image enhancement: linear (negative and identity transformations), logarithmic (log and inverse-log transformations), and power-law (nth power and nth root transformations).The identity function is the trivial case in which output intensities are identical to input intensities. It is included in the graph only for completeness.

3. Which expression is obtained by performing the negative transformation on the negative of an image with gray levels in the range[0,L-1] ?
a) s=L+1-r
b) s=L+1+r
c) s=L-1-r
d) s=L-1+r

Explanation: The negative of an image with gray levels in the range[0,L-1] is obtained by using the negative transformation, which is given by the expression: s=L-1-r.
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4. What is the general form of representation of log transformation?
a) s=clog10(1/r)
b) s=clog10(1+r)
c) s=clog10(1*r)
d) s=clog10(1-r)

Explanation: The general form of the log transformation: s=clog10(1+r), where c is a constant, and it is assumed that r ≥ 0.

5. What is the general form of representation of power transformation?
a) s=crγ
b) c=srγ
c) s=rc
d) s=rcγ

Explanation: Power-law transformations have the basic form: s=crγ where c and g are positive constants. Sometimes s=crγ is written as s=c.(r+ε)γ to account for an offset (that is, a measurable output when the input is zero).

6. What is the name of process used to correct the power-law response phenomena?
a) Beta correction
b) Alpha correction
c) Gamma correction
d) Pie correction

Explanation: A variety of devices used for image capture, printing, and display respond according to a power law. By convention, the exponent in the power-law equation is referred to as gamma .The process used to correct these power-law response phenomena is called gamma correction.

7. Which of the following transformation function requires much information to be specified at the time of input?
a) Log transformation
b) Power transformation
c) Piece-wise transformation
d) Linear transformation

Explanation: The practical implementation of some important transformations can be formulated only as piecewise functions. The principal disadvantage of piecewise functions is that their specification requires considerably more user input.

8. In contrast stretching, if r1=s1 and r2=s2 then which of the following is true?
a) The transformation is not a linear function that produces no changes in gray levels
b) The transformation is a linear function that produces no changes in gray levels
c) The transformation is a linear function that produces changes in gray levels
d) The transformation is not a linear function that produces changes in gray levels

Explanation: The locations of points (r1,s1) and (r2,s2) control the shape of the transformation function. If r1=s1 and r2=s2 then the transformation is a linear function that produces no changes in gray levels.

9. In contrast stretching, if r1=r2, s1=0 and s2=L-1 then which of the following is true?
a) The transformation becomes a thresholding function that creates an octal image
b) The transformation becomes a override function that creates an octal image
c) The transformation becomes a thresholding function that creates a binary image
d) The transformation becomes a thresholding function that do not create an octal image

Explanation: If r1=r2, s1=0 and s2=L-1,the transformation becomes a thresholding function that creates a binary image.

10. In contrast stretching, if r1≤r2 and s1≤s2 then which of the following is true?
a) The transformation function is double valued and exponentially increasing
b) The transformation function is double valued and monotonically increasing
c) The transformation function is single valued and exponentially increasing
d) The transformation function is single valued and monotonically increasing

Explanation: The locations of points (r1,s1) and (r2,s2) control the shape of the transformation function. If r1≤r2 and s1≤s2 then the function is single valued and monotonically increasing.

11. In which type of slicing, highlighting a specific range of gray levels in an image often is desired?
a) Gray-level slicing
b) Bit-plane slicing
c) Contrast stretching
d) Byte-level slicing

Explanation: Highlighting a specific range of gray levels in an image often is desired in gray-level slicing. Applications include enhancing features such as masses of water in satellite imagery and enhancing flaws in X-ray images.

12. Which of the following depicts the main functionality of the Bit-plane slicing?
a) Highlighting a specific range of gray levels in an image
b) Highlighting the contribution made to total image appearance by specific bits
c) Highlighting the contribution made to total image appearance by specific byte
d) Highlighting the contribution made to total image appearance by specific pixels

Explanation: Instead of highlighting gray-level ranges, highlighting the contribution made to total image appearance by specific bits might be desired. Suppose , each pixel in an image is represented by 8 bits. Imagine that the image is composed of eight 1-bit planes, ranging from bit-plane 0 for the least significant bit to bit-plane 7 for the most significant bit. In terms of 8-bit bytes, plane 0 contains all the lowest order bits in the bytes comprising the pixels in the image and plane 7 contains all the high-order bits.

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