Computational Vision CSCI 363, Fall 2018 Lecture 25 Review for Final Exam

1. Computational VisionCSCI 363, Fall 2018Lecture 25Review for Final Exam

2. Structure from Motion questions Describe the Incremental Rigidity Scheme. What are the advantages of using the Incremental Rigidity Scheme over other methods? Describe how depth estimates can be made from the measured image velocities.

3. Computation of Image Velocity Given the image velocity equations: where x = X/Z and y = Y/Z. Suppose Tx = 3 deg/sec, Ty = 2 deg/sec and Tz = 6 deg/sec What is the image velocity for a point P = (6, 4, 2)?

4. Computing Heading Suppose an observer is moving in a straight line. Given the following two image velocity vectors and their positions, compute the position that coincides with the observer’s heading. v1 = (2, 1) for a point located at (5, 3) in the image v2 = (-1, 3) for a point located at (2, 5) in the image.

5. Heading Questions • List 3 sources of information people can use to compute heading. • What is the pattern of the optic flow filed for an observer moving in a straight line? How can we compute heading from it? • Explain the evidence that humans make use of eye movement information when computing heading. • Explain how one can use vector subtraction of image velocity vectors to compute observer heading in the presence of rotations. • How might neurons do the motion subtraction described above? • What effect does a moving object have on the computation of heading? • What is the evidence that MSTd neurons are involved in computing heading. Describe at least 2 pieces of evidence.

6. Color Given three colors, A, B, andC, in color space, shown below, diagram how one can produce a fourth color, D, from a linear combination of A, B and C. B D C A

7. Color Receptors Given the single photoreceptor response profile below, explain why one cannot distinguish between color x and color z. Given a second photoreceptor response, shown below, explain how one can now distinguish between x and z.

8. Color Essay Questions • Why can we match any perceived color with the appropriate combination of red, green and blue light? • What is the psychophysical evidence that color perception is organized into pairs of complementary colors (color opponency)? • What is color adaptation? • Given an R+/G- color opponent cell, diagram the responses to the following stimuli: • A small red spot in the center • A large red spot • A large white spot • What is color constancy? • What is color blindness and what causes it?

9. Retinex Theory • Given the following surfaces and illumination gradient, • a) Calculate the ratio of perceived brightness between the front and back surfaces. • b) Calculate the ratio of actual brightness between the bottom of the front surface and the top of the back surface. 100% 20% 70% 40% 30% 60% 20%

10. Perceptual OrganizationQuestions What are the stages of perceptual organization? Name 3 principles of Figure/Ground organization and briefly describe each one. Why is meaningfulness of a shape problematic in terms of distinguishing figure from ground? What is the evidence that V1 cells distinguish figure from ground?

11. Visual Occlusion What is the evidence for the filling-in process known as interpolation? What is visual (or amodal) completion? What is the Kanisza Triangle? What does it tell us about the perception of edges? How do cells in visual area V2 respond to illusory contours?

12. Attention When searching for a target among distracting objects, how do we distinguish efficient from inefficient search? What is change blindness? Give an example of when this could occur. What is inattentional blindness? Give an example of when this could occur in everyday life.