Machine Vision 1 TURN OVER
Machine Vision, Alternative Assessment, replacing 2019/2020 Final Exam
For: COMP0137 and COMPGI14 (for all current and previous students)
You must answer ALL questions on ALL pages of this assignment.
Marks for each part of each question are indicated in square brackets [n].
Implementing your own code and using slides, videos, and your own notes from this class
ARE permitted. You may also access books, published papers, and existing Wikipedia
articles online. But other online-resources, communications with others, and any
collaboration are strictly NOT permitted. Posting or sharing your work with others,
complete or incomplete, is NOT permitted.
Further, you are expected to abide by the UCL Academic Manual, especially with respect to
academic integrity.
Section A: A Graphical Model
1. There is a Markov Model pictured below. Each discrete variable is illustrated to
show what values are possible. A "configuration" is a specific combination, where
each xi is in a specific state, for i=1..5. The unary costs, pairwise costs, and triplet
costs for each variable or combination of variables are specified in the tables
provided.
All variables are discreet, but they do not all have the same number of possible
states. For example, variable X1 can be “A” or “B”, while X2 can be “C”, “D”, or “E”.
The unary costs for all five variables are:
x
1
x
2
x
3
x
4
x
5
Machine Vision 2 CONTINUED

The pairwise and triplet costs are here:


Use the above information to answer the following questions.

(a) Configuration A is ACGJN. Compute the total cost of this configuration: _____
[7 marks]
(b) Configuration B is AEFKM. Compute the total cost of this configuration: _____
[7 marks]
(c) What is the Maximum Likelihood configuration? _ _ _ _ _
[7 marks]
(d) What is the Maximum a Posteriori configuration? _ _ _ _ _
[8 marks]
[Total for Question 1: 29 marks]
Section B: Cloud Tracking Task
2. You are installing two outdoor cameras to look up at the sky, each with a wide
field of view. Your aim is to track some of the more distinct points on passing
clouds, so you can infer their velocity in meters/second. An example image is
shown below.
[Question cont. over page]
Machine Vision 3 TURN OVER


[Question 2 cont.]

“Clouds” Photo by Chris.L.Dodds,CC BY-SA 2.0
(a) You must choose the locations where the two cameras will be placed. Relative to
the first camera, the second one should be placed what distance away?
Multiple choice: 0.5 m / 50 m / 500 m / 5000 m Answer: _______
[6 marks]
(b) You must choose an interest-point detector, to find the distinct points that will be
tracked by your system. Which detector would you choose?
Multiple choice: FAST / SUSAN / Canny / SIFT / DoG Answer: _____________
[6 marks]
(c) Do the cameras need to be genlocked? ("Genlock" stands for generator locking)
Answer: __True or False?___
[4 marks]
(d) Describe how telemetry of a single airplane helps you with this overall task.
Comment on the need or benefit of having multiple airplanes. (Your answer must
be 4 sentences or shorter.)
______________________________________________________________________________________________
______________________________________________________________________________________________
_____________________________________________________________________________________________

Machine Vision 4 CONTINUED

[Question 2 cont.]
____________________________________________________________________________________________
[7 marks]
(e) How will your system deal with the fact that each cloud may be at a different
altitude? (Your answer must be 2 sentences or shorter.)
____________________________________________________________________________________________
____________________________________________________________________________________________
[6 marks]
[Total for Question 2: 29 marks]
Section C: Miscellaneous Questions
3. Describe a unique computer vision classification task, naming three or more
categories that you'd want to distinguish. The task must have severely imbalanced
classes, and you must explain what you would do to cope with that imbalance.
(Your answer must be 4 sentences or shorter.)
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
[12 marks]
4. Does class imbalance have a counterpart in regression tasks? What process would
you follow to check for it? (Your answer must be 3 sentences or shorter.)
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
[9 marks]
[Questions continued on next page]

Machine Vision 5 END OF PAPER

5. You want to train a model with many parameters. Then you learn from an oracle
that one (1) of the training labels is wrong. Describe one efficient way that may
identify which training example had the wrong label? (Your answer must be 3
sentences or shorter.)
____________________________________________________________________________________________
____________________________________________________________________________________________
____________________________________________________________________________________________
[9 marks]
6. Generative and Discriminative Models have different strengths and weaknesses.
For each of six sub-questions, answer “G” or “D” (if Generative vs Discriminative is
better) or “B” for Both, or “N” if neither is clearly preferable over the other.
6.a: Your input vector x is missing data in some dimensions: __________
6.b: You have no access to a prior: __________
6.c: You have access to a prior: __________
6.d: Your model has only few parameters: __________
6.e: You want to draw samples from your model: __________
6.f: Your world-state is high-dimensional: __________
[12 marks total]
[Total for Question 3, 4, 5, and 6: 42 marks]









[Total for all questions: 100 marks]