Midterm Solution. - University of British Columbia CPSC 425

CPSC 425 Midterm Exam February 14, 2019 Time: 75 minutes Total Marks: 68 Name (Print – Surname First) UBC Student Number Signature SPECIAL INSTRUCTIONS: 1. Before beginning. . . – In ink, provide your name, studen ...

CPSC 425 Midterm Exam February 14, 2019 Time: 75 minutes Total Marks: 68 Name (Print – Surname First) UBC Student Number Signature SPECIAL INSTRUCTIONS: 1. Before beginning. . . – In ink, provide your name, student number, and usual signature above. – Place your UBCcard at a spot nearby visible to the exam invigilators. 2. This exam is closed book. Answer all questions in the space provided. You may use pencil or pen. Write legibly. Keep your answers short. If you run out of space for a question, you probably have written too much. If you do need more space for a question, use the back of a page and clearly indicate the location of your answer. 3. Use the number of marks allocated to each question to help you determine how much time you should spend on that question. UNIVERSITY REGULATIONS: – No candidate shall be permitted to enter the examination room after the expiration of one half hour, or to leave during the first half hour of the examination. Marks 1-6 /25 7 /8 8 /6 9 /11 10 /6 11 /8 12 /4 Total /68 – CAUTION: Candidates guilty of any of the following, or similar, dishonest practices shall be immediately dismissed from the examination and shall be liable to disciplinary action. 1. Having at the place of writing, or making use of, any books, papers or memoranda, electronic equipment, or other memory aid or communication devices, other than those authorized by the examiners. 2. Speaking or communicating with other candidates. 3. Purposely exposing written papers to the view of other candidates. The plea of accident or forgetfulness shall not be received. – Candidates must not destroy or mutilate any examination material; must hand in all examination papers; and must not take any examination material from the examination room without permission of the invigilator. THIS EXAMINATION CONSISTS OF 6 PAGES. CHECK TO ENSURE THAT THIS PAPER IS COMPLETE. Part A: Multiple Part True/False Questions. For each question in Part A, indicate which of the statements, (A)–(D), are true and which are false? Note: Questions in Part A may have zero, one or multiple statements that are true. Question 1: [4 marks] Which of the following statements are true of the focal length, f, of a lens? Which are false? (A) The focal length, f, depends on the geometry (i.e., shape) of the lens. (B) The focal length, f, depends on the index of refraction of the material used to make the lens. (C) The focal length, f, depends on the wavelength (i.e., colour) of the light imaged. (D) The focal length, f, depends on the distance from the centre of the lens to the image plane. Solution : (A) True, (B) True, (C) True, (D) False Question 2: [4 marks] Under standard perspective projection, which of the following properties are true and which are false, in general? (A) Straight lines project to straight lines. (B) Parallel lines project to parallel lines. (C) Distant objects appear smaller. (D) Angles are preserved. (E) Sphere in the world can appear as an ellipse in the imaging plane. Solution : (A) True, (B) False, (C) True, (D) False, (E) True Question 3: [4 marks] We can detect an object in an image by performing normalized cross-correlation of a template with the image and selecting the matches that are above a certain threshold. In order to detect the object at a range of different sizes, one approach is to correlate templates of increasing size with the image. Another approach is to build a Gaussian pyramid and to convolve a fixed-size template with each level of the pyramid. Which of the statements, (A)–(D), are true of the Gaussian pyramid approach and which are false? (A) The higher levels of the pyramid have fewer pixels, which reduces the cost of cross-correlation compared to using larger templates on the original image. (B) The cost of creating new levels of the pyramid is less than the cost of creating larger versions of the template. (C) It takes fewer operation to correlate templates with fixed sizes then ones with increasing sizes. (D) The higher levels of the pyramid avoid aliasing that occurs with increasing template sizes. Solution : (A) True, (B) False, (C) True, (D) False Question 4: [4 marks] Which of the following statements are true of the 2D Laplacian of the Gaussian (52G)? Which are false? (A) The 2D Laplacian of the Gauss