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COMP6021 Media Data Formats
Sample Questions
There are no past papers for this module because it is being offered for the first time in Winter 2010.
Here are some questions I have asked in the past on topics that form part of this module. They are in
no particular order. There are many topics that are covered by this module only. There are no
questions associated with those topics. So this list of questions should not be considered to be
complete.
These should give you an idea of the way I ask questions.
I will provide more information about the format of the final exam, one I have written it!
Q1. (15 marks)
Zogese is a language with only 16 characters.[14 letters, a space, a full-stop]. As a result, computer
systems in Zoglandia use only 4 bits per character. The table below shows each of the characters
and its code.
Part A
Explain how variable length codes could be used to reduce the number bits used to store Zogese
text. (10 marks)
Character
●
A
E
O
B
D
K
M
Code
0000
0001
0010
0011
0100
0101
0110
0111
Frequency
13
10
10
8
7
5
5
5
Character
P
R
T
V
Z
F
H
Space
Code
1000
1001
1010
1011
1100
1101
1110
1111
Frequency
4
4
4
2
1
1
1
20
Part B
Propose an appropriate alternative table that employs variable length codes.
Note: Your proposed table need not be optimal (5 marks)
Q2. (5 marks)
What is the origin of the acronym “MP3”.
Q3. (15 marks)
There are two kinds of cells sensitive to light in the human retina. What are they called? (10 marks)
Which is responsible for color vision?
(5 marks for correct answer.)
(zero marks for no answer)
(minus 5 marks for incorrect answer)
Q4. (10 marks)
An uncompressed black and white image has 128 shades of grey. If it is 400 x 400 pixels, how
many Kbytes would you expect it to be?
Q5. (5 marks)
What (decimal) RGB values would you expect pink to have?
Q6. (5 marks)
In the Lab color system what does the value of L represent?
Q7. (10 marks)
In the Lab color system what does the value of a represent?
Q8. (20 marks)
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
The table above shows three differently colored pixels that have been used to simulate a color by
dithering.
A is R:200 G:100 B:050
B is R:100 G:050 B:100
C is R:100 G:000 B:000
What are the RGB values of the color being simulated?
Q9. (5 marks)
What is the principle compression technique used by GIF?
Q10. (10 marks)
What is the difference between interframe video compression and intraframe video compression.
Q4
Part A (5 marks)
What is image subsampling?
Part B (5 marks)
What is dithering?
Part C ( 15 marks)
A colour with RGB values of 200, 120 and 60 respectively is simulated using two colours dithered
in the pattern shown below. If the RGB values of colour A are 100, 60 and 20, what RGB values
would you expect colour B to have.
A
B
B
A
B
B
A
B
B
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
A
B
B
A
B
B
A
B
B
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
A
B
B
A
B
B
A
B
B
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
A
B
B
A
B
B
A
B
B
A
B
B
B
B
B
B
B
B
B
B
B
B
B
B
Q. 2
Explain in detail how the MPEG compression standard encodes digital video.
In particular your answer should refer to the different types of frames and their relative sizes; and
should explain why frames may be transmitted in an order different from the order in which they
are displayed.
Q. 3
A
What is pixel depth? (2 marks)
B
What is resolution? (2 marks)
C
What is sub-sampling? (2 marks)
D
A sound sample is converted from 44Hz to 11Hz. What specific effect would this have on the sound
quality? (2 marks)
F
What kind of compression does GIF use? (2 marks)
G
What is the maximum number of colours that can be saved using the GIF? (2 marks)
H
What does the acronym JPEG stand for? (2 marks)
Part I (9 marks)
“Although colour has a physiological basis, the way humans respond to colour is heavily influenced
by cultural factors”. Discuss
B.
What colour is #000000? (2 marks)
C.
What colour is #FFFF00? (2 marks)
D.
What colour is #CCCCC? (2 marks)
E.
What CMYK values would black have? (2 marks)
F.
What Lab values would dark grey have? (2 marks)
Q3.
An MPEG video file comprises frames of three types.
What are these three types called?
(9 marks)
Briefly outline the dependencies that exist between the three types of MPEG frame.
(11 marks)
A sequence of MPEG frames is transmitted in the following order
33 37 34 35 36 41 38 39 40 44 41 42 43
For each frame in this sequence, identify the type of the frame. (13 marks)
Q3.
Part A (5 marks)
What is progressive image coding?
Part B (10 marks)
Explain in details how GIF images may be stored in a progressive format.
Part C (5 marks)
Illustrate how R:50 G:0 B:100 might be simulated by dithering with two colours.
Part D (5 marks)
A 1028 x 256 pixel indexed colour image with 117 colours is stored in a raw format without further
compression. How many Kb would you expect it to be?
Q2.
A language has 12 symols. The table below lists the frequencey with which these symbols occur in
the language. Use Hufffman’s algorithm to devise optimal variable length codes for the symbols.
(50 marks)
Symbol
E
T
A
N
Frequency
50
15
10
10
Symbol
Q
X
K
W
Frequency
1
3
10
5
Q2. (25 marks)
Part A (16 marks)
Outline each of the steps taken by the JPEG compression algorithm to compress an image.
[You need not address the decompression.]
Part B (6 marks)
What does it mean when a compression algorithm is said to be symmetrical?
Part C (3 marks)
Is JPEG symmetrical or asymmetrical?
Part A (25 marks)
Color
1
2
3
4
5
6
7
8
R
100
0
0
25
0
10
50
255
G
25
0
0
50
0
100
25
200
B
200
25
0
250
200
220
100
255
Color
9
10
11
12
13
14
15
16
R
200
50
100
0
255
220
100
100
G
0
0
25
0
50
25
10
0
B
50
0
200
200
255
0
0
200
The color lookup table above lists the RGB values of the 16 colors in an image palette. The color
with RGB values of R: 25 G:0 B:200 is desired but is not present and so must be simulated by
dithering. Devise a dithering scheme that simulates the missing color using a combination of those
available.
Question
The Citese language has only 12 symbols. These are listed below along with the frequency with
which they occur in written Citese.
Using Huffman’s algorithm, devise a variable length coding system for Citese that minimises the
length of Citese documents.
Symbol
A
B
C
D
E
F
Frequency
.3
.01
.01
.02
.4
.01
Symbol
O
I
U
T
N
R
Frequency
.05
.02
.02
.09
.04
.03
Q3. (25 marks)
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
A
C
C
C
A
C
C
C
C
C
B
C
C
C
B
C
The table above shows three differently coloured pixels that have been used to simulate R:200 G:20
B:60 by dithering.
A is R:190 G:100 B:050
B is R:100 G:040 B:100
Part A (17 marks)
What RGB values does C have?
Part B (8 marks)
Propose an alternative 2-colour dithering scheme for R:190 G:20 B:60
Q. 2 (25 marks)
Part A (7 marks)
Zogese is a language with only 16 characters.[14 letters, a space, a full-stop]. As a result, computer
systems in Zoglandia use only 4 bits per character. The table below shows each of the characters, its
binary code, and the frequency with which the character occurs in Zogese text.
Explain how variable length codes could be used to reduce the number bits used to store Zogese
text.
Character
●
A
E
O
B
D
K
M
Code
0000
0001
0010
0011
0100
0101
0110
0111
Frequency
13
10
10
8
7
5
5
5
Character
P
R
T
V
Z
F
H
Space
Code
1000
1001
1010
1011
1100
1101
1110
1111
Frequency
4
4
4
2
1
1
1
20
Part B (10 marks)
Propose an appropriate alternative table that employs variable length codes.
[Your table need not be optimal]
Part C (8 marks)
What is run length encoding?
Q.3 (25 marks)
Part A (6 marks)
Explain how the distribution of different types of cells in the human eye results in difficulty in
perceiving colour at the periphery of the visual field.
Part B (7 marks)
Briefly outline how JPEG exploits weakness in human vision to achieve compression
Part C (5 marks)
What is progressive coding?
Part D (7 marks)
Explain in detail how GIF codes images progressively.
Q1 (50 marks)
Part A
The table below shows the relative frequencies with which 16 characters occur in a particular
language. Use Huffman’s algorithm to construct an optimal variable length code for the language.
(40 marks)
A
B
C
D
E
F
G
H
7
1
3
2
15
2
3
4
I
L
M
N
O
P
R
S
6
5
1
6
6
1
6
6
Part B
How would the sting “COMRULES” be expressed using this variable length code? (5 marks)
Part C
For “COMRULES” what percentage saving do the variable length codes offer over the fixed
length? (5 marks)
Q2. (25 marks)
Q2. (25 marks)
Part A
The table below shows the relative frequencies with which 8 characters occur in a particular
language. Use Huffman’s algorithm to construct an optimal variable length code for the language.
(13 marks)
A
E
O
C
K
N
M
R
7
1
3
2
15
2
3
4
Part B
How would the string “CORK” be expressed using this variable length code? (2 marks)
Part C
For “CORK” what percentage saving (if any) do the variable length codes offer over the fixed
length? (5 marks)
Part D
Koruku Tech Corporation uses Huffman in its television remote controls. List two keys would you
expect to have short codes. (3 marks)
Part E
In Morse code T is -. Q is --.-. Why do you this Morse chose these values? (2 marks)
Q4.
Part A (15 marks)
Explain how the illusion of 3D is generated by anaglyphs when viewed with Red – Cyan glasses.
Part B (10 marks)
Kokuru Tech Corp will introduce a new type of anaglyph that uses different colours. If one of the
colors is Green (R:0 G:255 B:0), what would you expect the other colour to be? Why?
Q. 2 (25 marks)
Part A (12 marks)
Explain how variable length codes can be used to reduce the number of bits required to store text.
Illustrate you answer with an alphabet of 8 symbols and table of variable length codes.
Part B (8 marks)
What is run length encoding?
Part C (5 marks)
What is meant by a palette clash?
Q.3 (25 marks)
Part A (12 marks)
Explain how the distribution of different types of cells in the human eye results in difficulty in
perceiving colour at the periphery of the visual field.
Part B (13 marks)
“Although colour perception has a physiological basis, the way humans experience colours in
heavily influenced by cultural factors.” Explain and discuss
Q.5 (25 marks)
Part A (15 marks)
MPEG video files contain I frames, P frames, and B frames. Briefly describe how each type of
frame is coded and explain with the aid of a diagram how the frames relate to each other.
Part B (5 marks)
MPEG Compression is said to be asymmetrical. What does this mean?
Part C (5 marks)
Which part of the MPEG compression algorithm give rise to asymmetry?
Congratulations on reading this document all the way to the end. Your interest bodes well for
your success in this module.
Colin M