EEE8098 IMAGE PROCESSING AND COMPUTER VISION SEMESTER 2 2018 / 2019
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EEE8098
SEMESTER 2 2018 / 2019
IMAGE PROCESSING AND COMPUTER VISION
Section A
1.
a. A 25 pixel image has the gray levels 0,1,2,3 with the spatial distribution shown in Figure 1a.
i Based on a position operator; one pixel down, one pixel to
the right, derive the column-row co-occurrence matrix for this image
ii Calculate the descriptor uniformity that characterises the co-
occurrence matrix [6 Marks]
1 |
2 |
2 |
1 |
3 |
2 |
0 |
0 |
2 |
1 |
1 |
1 |
3 |
0 |
3 |
2 |
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2 |
2 |
3 |
0 |
0 |
3 |
1 |
2 |
Figure 1a
b. Explain what is meant by the terms “Chain Codes” and
“Signatures” in the context of object representation. [6 Marks]
c. Figure 1b shows an object superimposed on a grid. Starting at point X and using 8-point connectivity determine the:
i. The chain code for the object. Present your data as a minimum value integer
ii. Make your code independent of rotation and determine the shape number of the object
iii. Using D4 distance measure and the centre reference point, derive a signature for the object [12 marks]
X Reference Point
Figure 1b
d. Derive a value for this measure of smoothness, to 3 significant figures, for each of the two 6x5 binary images shown in Figure 1c. Comment on your results. [6 Marks]
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Figure 1c
2.
a) Figure 2a shows a part of an image with thresholded pixels marked with an X. Using the Hough transform with the angles
-45,-300, 00, 300, 450
i Construct an accumulator array with ‘hits’ ≥ 2
ii Determine any corresponding straight lines using Cartesian
co-ordinates. [9 Marks]
x/y 0 1 2 3 4 5 6
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Figure 2a
b) In an image P1 = 3e−2z represents the background and
P2 = 2e−z represents the object. The boundary condition is
0 ≤ z ≤ 4. What is the optimal threshold value to segment the object from the background? [9 Marks]
c) A 5x5 image and the Sobel masks hx and hy are given in Figure 2b, compute the:
i gradient of the image
ii orientation of the image
iii Given the threshold is 550 < T <1000, how many edges are
detected and what is the orientation? [12 Marks]
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255 |
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255 |
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255 |
-1 |
-2 |
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hx
Figure 2b
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-2 |
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hy
3.
a. Give a block diagram for:
i a lossless predictive compressor and decompressor
ii a lossy predictive compressor and decompressor [10 Marks]
b. Using the information in Figure 3a, tabulate your results to show: i the lossless predictor compressor/decompressor is error free ii the lossy predictor compressor/decompressor is not error free [10 Marks]
Row of pixels |
90 |
87 |
100 |
103 |
The prediction coefficient = 1 for all predictors Quantiser is defined as = 4 if the error ≤ 0 otherwise = +4 |
Figure 3a
c. Explain the ‘Block Truncation Coding’ technique used for image compression. [4 Marks]
d. Figure 3b shows a 4x4 gray level image. Determine the: i Block Truncation Coding for this image
ii The estimated image by decoding the Block Truncation Coding iii The root mean square error between the estimated and original
image [6 Marks]
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93 |
103 |
106 |
101 |
91 |
105 |
99 |
84 |
66 |
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Figure 3b
Section B
4.
a. Figure 4a shows the number of gray levels in an image. Determine the following:
i Entropy of the image
ii Huffman codes for the gray levels
iii Average word length for the Huffman codes
iv Efficiency of the Huffman codes [10 Marks]
Gray level |
Number |
G1 |
40 |
G2 |
25 |
G3 |
125 |
G4 |
60 |
G5 |
150 |
G6 |
100 |
Figure 4a
b. Give the pseudo algorithm to:
i. encode a message using Arithmetic coding
ii. decode a message using Arithmetic coding [10 Marks]
c. Given the sample symbol ranges in Figure 4b, where ‘e’ is the terminating character. Encode the message ‘dace’ using arithmetic coding.
Symbol |
Probability |
a |
30% |
2023-05-23