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CMT107
Visual Computing
Start time of Examination: 10am GMT
Duration: 2 Hours
Additional Time: 30 minutes to upload the paper at the end of the exam.
Please read the following information carefully:
Structure of Examination Paper:
• There are 6 pages including this page.
• There are 4 questions in total.
• There are no appendices.
• The maximum mark for the examination paper is 100 and the mark obtainable for a
question or part of a question is shown in brackets alongside the question.
Conduct during the exam.
You are now under exam conditions: -
• The only device which should be switched on is the device used to complete this exam.
• All other electronic devices, such as mobile phones, smart watches, fitbit, etc must be
switched off.
• Contacting other students, through electronic means or face to face during the exam will be
classed as cheating and may be reported for Academic Misconduct.
• Discussions with Family members /flat/house mates entering the room during the exam will
be class as cheating and may be reported for Academic Misconduct.
Instructions for completing the examination:
• Answer all questions.
• Add your student number to all documents uploaded.
• Make sure you save your answers as you go through the exam.
• Remember to upload/submit your answers at the end of the exam and wait for confirmation
that it has been received.
• You have 30 minutes from the end of the exam to upload the document.
Module Code: CMT107
2
• On the front page of your document, please summarise the question numbers you have
answered.
• In addition to contacting your school, if you experience technical difficulties during the exam
take a photo or screenshot of any error messages, detail how long the problem occurred
and report extenuating circumstances after the exam.
Module Code: CMT107
3
Q1. Vectors and Transformations
(a) Assume that a and b are two unit vectors in ℛ3. What do the angles between a and b correspond to
in the following computation results, giving your reasoning:
(i) ∙ = 0
(ii) ∙ = −1
(iii) | × | = 0
(iv) | × | = 1
[8]
(b) The three vertices of a triangle are represented by the following homogeneous
coordinates: ̅0 = [2,0,0,2], ̅1 = [0,1,2,1], ̅2 = [2,2,0,1].
(i) Give the Cartesian coordinates of ̅0. [2]
(ii) Give the homogeneous representation of the direction vector from ̅0 to ̅1. [2]
(iii) Compute the unit normal vector of this triangle. [3]
(c) Fixing the reference frame and transforming an object (object transformation) can be equivalently
represented by fixing the object and transforming the reference frame (coordinate transformation).
Suppose a coordinate transformation consists of a rotation around z axis by 90◦, followed by a
translation by (1, 2, 0).
(i) Describe its equivalent object transformation.
(ii) Give the homogeneous matrix representation of this transformation.
(iii) Given a point (1, 0, 1) in the object coordinate system, compute its new coordinates in the
camera coordinate system. [10]
Module Code: CMT107
4
Q2. Graphics
(a) Given a triangle mesh, briefly explain the key differences in how triangle normals are used to
evaluate (i) flat shading, (ii) Gouraud shading, and (iii) Phong shading. [6]
(b) A triangle surface with vertices p0, p1, p2 is lit by a point light source with light intensity L and
position pL. The viewer position is pV. Let p be centroid of the triangle. State the formula for
Phong’s reflection model to compute the light reflected from the point p, using p0, p1, p2, pL, pV
and p to define any necessary intermediate quantities in the formula. It is assumed that the material
properties of the surface are known, and you can use any symbols to represent the material
properties in stating the formulae. [9]
(c) Starting with G, build a BSP tree for the scene shown below. Represent the ‘+’ side of each cutting
plane as the left child and the ‘-’ side as the right child. Explain your reasoning.
[10]
Module Code: CMT107
5
Q3. Image Processing
(a) The pixel values of an image and a filter kernel (denoted by ) are given in the two tables below.
2 3 3 8 7
6 4 2 0 3
3 5 1 3 4
5 6 8 7 2
4 1 9 0 5
(i) Compute the filtering result of the pixel in the centre of the image (with value 1) using the filter kernel
. [2]
(ii) Compute the filtering result of the pixel in the middle of the top row (with value 3) using the filter
kernel , based on copy edge boundary extension. [3]
(b) What properties are required for a kernel to be used to detect edges? Which of the following kernels can
be used to detect edges? Give your reasons. [10]
(c) Images and are shown below with the cross in the left bottom showing their correspondence. Design
an appropriate structuring element such that can be obtained after dilating . (black for 1 and white for
0).
Note: mark the centre of the structure element clearly. [10]