Computer Science 455

Instructor: R. P. Burton

Sixth Quiz

March 31-April 1, 2008

Name _________________________________________ Score ____________/48

1. A scene represented in an octree
1. does not lend itself well to visible element determination
2. lends itself well to visible element determination for a small number of views
3. lends itself well to visible element determination for an arbitrary view

(b)

2. For purposes of determining the illumination of a surface, all of the following should be considered EXCEPT
1. the positions of light sources
2. the intensity of light sources
3. the colors of the light sources
4. the geometry of the light sources
5. (no exceptions here)

(e)

3. For purposes of determining the illumination of a surface, all of the following should be considered EXCEPT
1. the opacity or transparency/translucency of the surface
2. the transparency or translucency of the surface
3. whether the surface is shiny, matte, or somewhere in between
4. the orientation of the surface relative to the light source
5. (no exceptions here)

(e)

4. As discussed in class, all of the following can be treated as a light source EXCEPT
1. a light-emitting source
2. a light-reflecting source
3. a light-transmitting source
4. (no exceptions here)

(d)

5. Which of the following is more likely to produce a diffuse reflection?
1. a flannel shirt
2. a pair of eye glasses
3. (both are equally likely to produce a diffuse reflection)
4. (neither is likely to produce a diffuse reflection)

(a)

6. Diffuse reflection is produced by
1. ambient light
2. point source light
3. both ambient and point source light
4. neither ambient nor point source light

(c)

7. The intensity of point source light on a surface area is ____ the angle of illumination.
1. independent of
2. dependent upon

(b)

8. A specular reflection from a shiny surface (such as a polished apple or Christmas tree ornament) is ______.
1. white
2. the same color as the incident light

(b)

9. For an ideal reflector and a highly focused incident light source (perhaps a laser), the specular reflection can be seen along only one ray leaving the reflecting surface.
1. true
2. false

(a)

10. How is it possible to distinguish chrome from sterling silver from polished nickel of the same color and shineness?
1. it’s not possible
2. by the manner in which the intensity falls off as the angle of illumination changes
3. by the manner in which the intensity falls of as the angle of view changes

(b)

11. When light enters a slab of glass of uniform thickness at an angle Θ relative to the surface normal, the angle ______ , relative to the surface normal and then exits the slab of glass ______.
1. decreases, collinear with the original direction
2. increases, collinear with the original direction
3. increases, parallel to the original direction
4. decreases, parallel to the original direction

(d)

12. Texture is LEAST appropriately achieved by
1. micropolygonization of the surface
2. applying surface patterns
3. altering surface normals
4. altering reflection coefficients

(a)

13. 2D surface patterns can be applied to 2D surfaces, but, in general, not to surfaces of 3D objects.
1. true
2. false

(b)

14. In general, surface patterns should be applied _____ visible surface detection is done.
1. before
2. after
3. (it makes no difference)

(b)

15. When are shadows “provided?”
1. before hidden surface detection
2. after hidden surface detection, but using “hidden surface”-like techniques
3. after hidden surface detection, but without using “hidden surface”-like techniques

(b)

16. Shadows must be provided in
1. world coordinates
2. viewing coordinates
3. (it makes no difference)

(c)

17. Suppose you are in a remote region in a third world country and your display is such that pixels either are “on” of “off.” You cannot produce pictures in which the user sees several (“several” meaning > 2) levels of intensity.
1. true
2. false

(b)

18. Suppose a pixel actually consists of a 3 x 3 array of subpixels, each of which consists of a red, green, and blue component which either is on or off. How many different colors can the pixel have?
1. 3
2. 8 or 9
3. more than 9, but less than 500
4. 500 or more

(d: 10 x 10 x 10)

19. Continuing the previous problem, what is the maximum number of ways in which a color could be achieved?
1. just one
2. 8 or 9
3. more than 9, but less than 1000
4. 1000 or more

(d)

20. Dithering is characterized best as
1. a technique for creating the illusion of transparency by mixing foreground and background colors
2. a technique that antialiases by adding noise
3. making slight shifts in vertex positions to avoid intersections with scan lines
4. making slight shifts in vertex positions to achieve surface planarity

(b)

21. Constant intensity for a surface (sometimes achieved by treating incoming light rays as being parallel) is a computational convenience, but never produces a result which appears realistic.
1. true
2. false

(b)

22. Gouraud shading takes a surface approximated by a mesh of polygons and finds a Bezier or B-spline patch which approximates the surface.
1. true
2. false

(b)

23. Where does Gouraud shading first calculate intensities?
1. at vertices
2. along edges
3. along scan lines
4. (it doesn’t calculate intensities)

(a)

24. Gouraud got a Ph.D. from Sutherland for his shading technique. It was that cool!
1. true
2. false

(a)

25. What does Gouraud shading do to eliminate Mach bands?
1. it uses cubic interpolation rather than linear interpolation
2. it adjusts vertices to achieve higher continuity at the joints between patches
3. nothing; Gouraud-shaded images have Mach bands

(c)

26. How does Phong shading differ from Gouraud shading?
1. They are virtually identical; they represent simultaneous work done at different universities.
2. Phong shading eliminates Mach bands
3. Phong shading does a higher order interpolation
4. Phong shading considers only ambient light

(b)

27. How many rays must be sent into an arbitrary view volume to guarantee that every (visible) object in the view volume will be struck by a ray?
1. one for each pixel
2. one for each pixel corner
3. infinitely many

(c)

28. Sending a ray through every pixel corner instead of through pixel centers ___ the number of rays.
1. hardly impacts
2. virtually doubles
3. virtually quadruples

(a)

29. Ray tracing is ______ with antialiasing (surface boundaries)
1. compatible
2. incompatible

(a)

30. If 1000 x 1000 rays are sent into a scene with transparent and opaque surfaces, the total number of rays that must be processed
1. will be less than 1,000,000
2. will remain 1,000,000
3. may be greater than 1,000,000

(c)

31. Given that the faces of octants always are parallel to a principal plane, meaningful surface normals cannot be determined for scenes represented by octrees.
1. true
2. false

(b)

32. (Random) midpoint displacement techniques can be used to represent an object recognizable to most people as the Matterhorn (but probably not Mt. Everest since few will recognize its shape).
1. true
2. false

(a)

33. Radiosity models the phenomenon of a surface having the possibility to both give and receive illumination from other surfaces.
1. true
2. no, because this represents a multiple of unresolvable cycles
3. no for other reasons

(a)

34. How does radiosity incorporate the position of the viewer for the purposes of intensity calculations for diffuse surfaces?
1. by considering just the angle between the surface normal and the vector to the viewer
2. by considering the angles between the surface normal and the vectors all light sources, and the angle between the surface normal and the vector to the viewer
3. it doesn’t take into consideration the position of the viewer

(c)

35. The hundreds of thousands of colors to which the eye can respond represent ____ of the electromagnetic spectrum.
1. a small region
2. about half
3. the majority

(a)

36. Light emitted by the sun is ______of the visible spectrum.
1. at the low frequency end
2. at the high frequency end
3. near the middle of
4. (all of the above)

(d)

37. An object that has a real-world “color” (other than black or white) reflects only a single frequency, or at least a VERY narrow range of frequencies.
1. true
2. false

(b)

38. Which of the following is the most pure color?
1. red
2. white
3. black

(a)

39. If you wish to maximize the “bang for your buck” (or “rumble for your rupee,” or “shake for your shekel”), you would pick _____ primary colors on the chromaticity diagram.
1. two
2. three
3. four
4. infinitely many

(b)

40. What is the source of the standard primary colors?
1. the cones in the retina
2. the pioneering research of Roy G. Biv
3. a committee

(c)

41. The colors used for screen phosphors were chosen primarily to
1. accommodate the International Commission on Illumination
2. accommodate the standard primary colors
3. reflect Professor Biv’s pioneering work
4. accommodate the retina
5. keep costs down by using naturally occurring and commonly available phorphori

(d)

42. The colors used in screen phosphors represent “extremes” of the chromaticity diagram.
1. true
2. false

(b)

43. The majority of points in the chromaticity diagram have a single associated pure hue (i.e. frequency).
1. true
2. false

(a)

44. Virtually every color represented in the chromaticity diagram has a complementary color.
1. true
2. false

(a)

45. If you start with a pure hue and add black pigment, you are
1. shading
2. tinting
3. toning

(a)

46. Further pioneering work done by Roy G. Biv includes the development of the RGB color model, which, interestingly, bears his initials.
1. true
2. false

(b)

47. The CMY color cube has no corners which represent red, green, and blue.
1. true
2. false

(b)

48. The “primary colors,” now that we are adults, are
1. 1, 2, 3
2. red, yellow, and blue
3. cyan, magenta, and yellow

(c)