Code: AT-14                             Subject: IMAGE PROCESSING & COMPUTER GRAPHICS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

a. This is defined as the time taken by the emitted light from the CRT screen to decay to one-tenth of its original intensity.  

(A)  Random scan                               (B)  Persistence

(C)   Raster scan                                  (D)  Beam penetration

b. This is the smallest addressable screen element.  

(A)  Vector                                         (B)  Graphics

(C)  Frame                                          (D)  Pixel

             c.   Due to this lines have a jagged or stair step appearance when it steps from one row or column to the next  

(A) Scanning                                      (B)  Aliasing

(C) Thinning                                        (D) Thickening

             d.   The transformation matrix for mirror reflection with respect to the xy plane

(A) (B) 

(C) (D)

             e.   These algorithms are needed to determine which objects and surfaces obscure those objects and surfaces that are in back of them

(A) Mid Point algorithm.                      (B)  Hidden surface algorithms.

(C) Ray tracing algorithms.                   (D)  Perimeter algorithms.

             f.    This mechanical image digitizer uses a flat bed with the sensor moving in two linear directions.

(A) Microdensitimeters                        (B) Scanners

(C) Planars                                          (D) Xerox machines

             g.   When the threshold T depends on both the gray level values and some local property of this point, the threshold is called

(A)  Global threshold                           (B)  Local threshold

(C)  Dynamic threshold                        (D)  None of the above

             h.   This filter is effective in the presence of impulse noise, also called salt and pepper noise.

(A) Bandpass filter                              (B) Laplacian filter

(C) Median filter                                  (D) Highpass filter

             i.    This filter is called a __________ because it is a constant function with a hole at the origin.

(A) Laplacian filter                              (B) Edge detection filter

(C) Gradient filter                                (D) Notch filter

             j.    This frequency domain filtering procedure improves the appearance of an image by simultaneous gray-level range compression and contrast enhancement.

(A)  homomorphic filtering                   (B)  smoothing

(C)  edge linking                                  (D) sharpening

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Describe the two basic techniques for producing color displays with a CRT.                      (8)

             b.   Explain the steps involved in mid-point circle generation algorithm.  Enumerate the steps for drawing a circle of radius 10 units.                                (8)

Q.3     a.   Prove that a uniform scaling  and a rotation form a commutative pair of operations but that, in general, scaling and rotation are not commutative operations.                                              (8)

             b.   Clip line with end points (0,0) & (12,12) using Cohen Sutherland algorithm. The clipping rectangle is defined with bottom left edge as (1,1) and top right edge as (10,10).                                              (8)

Q.4     a.   Explain and derive the three dimensional transformation matrix for the following:

(i)   Translation                                    (ii)  Scaling.                                             (8)

b.   Explain homogeneous coordinate representation.  How is it useful?  Explain with an example.                                                                     (8)

Q.5     a.   What is meant by projection?  Define and derive the transformation matrix for the following projections:

(i)  Parallel                                           (ii)  Perspective.                                      (8)

     b.   Derive the rotation matrix for any axis that does not coincide with a coordinate axis using composite transformations.                                   (8)

  Q.6     a. Explain the basic concepts in sampling and quantization.  Describe how digital images are represented.                                                                   (8)

             b.   What is a histogram?  How is it calculated and plot?  Draw the histograms for a

                   (i)  dark                                               (ii)  bright

                   (iii) low contrast                                   (iv)  high contrast image.                          (8)

Q.7     a.   What are color models? Briefly explain the models used for colored printing.                      (8)

b.   Describe two-dimensional Fourier transform and explain the following properties

                   (i)  Translation                                     (ii)  Separability                                       (8)

Q.8     a.   Consider the following , 8-bit image of a vertical edge .  Enumerate the steps involved in coding its 16 pixels using the LZW coding algorithm.                        (10)

             b.   Explain a transform coding system.  Compare the transforms DFT, DCT and WHT.                       (6)

Q.9     a.   Explain how Hough transform is used for global processing.                                (8)

b.   What is optimal thresholding?  Suppose than an image has the gray-level probability density functions shown.  Here,  corresponds to objects and  corresponds to the background.  Assume that  and find the optimal threshold between object and background pixels.                       (8)