Computer Science 455

Instructor: R. P. Burton

Sixth Quiz

March 28-29, 2005

Name _________________________________________ Score ____________/47

1. The area subdivision algorithm contemplates a

   1. linear list

   2. tree structure

   3. graph

(b)

2. The complexity of the area subdivision algorithm is proportional to

   1. the number of subdivisions

   2. the visual complexity of the scene

(b)

3. Which of the following warrants further subdivision for the area subdivision algorithm?

   1. all surfaces are outside the area

   2. only one surface intersects the area

   3. a surrounder is closer that all surfaces which intersect the area

   4. (all contemplate further subdivision)

   5. (none contemplate further subdivision)

(e)

4. Hidden-element elimination can be achieved by traversing an octree in the proper order (painting contents during traversal).

   1. true

   2. only in your dreams

(a)

5. Which of the following visible element techniques does not lend itself well to hidden-line elimination?

   1. z-buffer

   2. scan-line

   3. depth-sorting

   4. area subdivision

   5. (all lend themselves well to hidden-line elimination)

(e)

6. What is the size of a “point light source?”

a. infinitesimally small

b. one pixel

c. small compared to the dimensions of the object

(c)

7. What is the source from which diffuse reflection can result?

   1. point light sources

   2. ambient light

   3. (either (a) or (b))

(c)

8. What is the source from which specular reflection can result?

   1. point light sources

   2. ambient light

   3. (either (a) or (b))

(a)

9. Diffuse reflection

   1. does not diminish as the angle of the incoming light changes

   2. falls off linearly with the angle of the incoming light

   3. falls off as the cosine of the angle of the incoming light

   4. falls off as the square of the angle of the incoming light

   5. falls off, but neither linearly, nor as the cosine, nor as the square of the angle of the incoming light.

(c)

10. Suppose a scene consists of ambient light and ten point light sources. Intensity is the sum of _____ components.

    1. two

    2. ten

    3. eleven

(c)

11. _________ consider(s) the direction to the viewpoint in determining intensity.

    1. Diffuse reflection

    2. Specular reflection

    3. Both diffuse and specular reflection

(b)

12. Specular reflection

    1. does not diminish as the angle of the incoming light changes

    2. falls off linearly with the angle of the incoming light

    3. falls off as the cosine of the angle of the incoming light

    4. falls off as the square of the angle of the incoming light

    5. falls off, but neither linearly, nor as the cosine, nor as the square of the angle of the incoming light.

(e)

13. When light enters a flat sheet of some transparent medium such as glass, the exit direction is _______ the entrance direction.

    1. collinear with

    2. parallel to, but not collinear with

    3. neither collinear with nor parallel to

(b)

14. Which of the following is NOT appropriate, in general, for achieving texture?

    1. messing with surface normals

    2. messing with reflection coefficients

    3. both (a) and (b) together

    4. using pattern fill methods

    5. (nothing generally inappropriate here)

(e)

15. Which best describes shadows?

    1. reflections cast by one object onto another objects

    2. the absence of contribution(s) from one or more light sources

(b)

16. Shadows are dependent on the viewing position.

    1. true

    2. false

(b)

17. Suppose you’re in a primitive setting where all the monitors display pixels that are either on or off – nothing in between. Suppose you determine to trade resolution for varying intensity levels by allowing the pixels to be 5 x 5. How many intensity levels can you achieve?

    1. 5

    2. 6

    3. 25

    4. 26

    5. 125

    6. 126

(d)

18. What is dithering?

    1. “faking” texture

    2. “painting” shadows

    3. another name for halftoning

    4. improving the appearance of an image by adding noise

(d)

19. Constant intensity across a surface is NEVER realistic.

    1. true

    2. false

(b)

20. Gouraud shading attempts to eliminate

    1. the polygonal appearance of the silhouette of a polyhedron

    2. boundaries between polygons approximating a polyhedron

    3. both (a) and (b)

(b)

21. Gouraud shading calculates intensities first

    1. at vertices

    2. along edges

    3. across scan lines

    4. at individual pixels

(a)

22. What is the fundamental difference between Gourand and Phong shading?

    1. one was developed in France, the other in Vietnam

    2. Gouraud produces polygonal silhouettes; Phong does not

    3. where intensities are calculated for the first time

(c)

23. Which is faster?

    1. Gouraud

    2. Phong

    3. (there is no appreciable difference)

(a)

24. A “ray” as used in ray tracing to determine the color of a pixel is

    1. like a mathematical ray, starting at the eye and passing through a pixel

    2. like a polyline

    3. like a cone

    4. like a “polycone”

(b)

25. If rays are sent through each pixel corner instead of each pixel center in a 1024 x 1024 display, the number of rays

    1. stays approximately the same

    2. approximately doubles

    3. approximately quadruples

(a)

26. An octree model defies shading because there is no information from which normals (and hence shades) can be determined.

    1. true

    2. false

(b)

27. What is the principal advantage of radiosity?

    1. extraordinary realism, albeit at a price

    2. calculation of illumination in a view-independent manner

    3. exploitation of coherence between frames in an animation (by caching)

(b)

28. In a scene consisting of n patches, to be rendered using radiosity, roughly how many form factors need to be determined?

    1. n

    2. n log n

    3. n²

    4. n!

(c)

29. The eye can _____ approximately 400,000 distinct ______colors.

    1. respond to, single frequency

    2. respond to, multiple frequency

    3. distinguish, single frequency

    4. respond to, multiple frequency

(a)

30. Of the following, which is the least pure color?

    1. red

    2. blue

    3. green

    4. white

(d)

31. Complimentary colors combine to produce

    1. white

    2. black

    3. an intermediate color other than white or black (in general)

(a)

32. The “best buy” number of colors for a color gamut is

    1. two

    2. three

    3. four

    4. (the more the better)

(b)

33. The standard primary colors are

    1. determined by nature

    2. determined by a committee and plausible

    3. determined by a committee, but not plausible

(b)

34. Red, green, and blue, as used in monitors, represent approximate extrema of the chromaticity diagram.

    1. true

    2. false

(b)

35. Where are the “pure hues” on the chromaticity diagram?

    1. throughout

    2. along the outside

    3. everywhere except along the outside

(b)

36. Alan artist adds white pigment to a pure hue. Peter painter adds black pigment to a pure hue. Alan is ____; Peter is ______.

    1. shading, tinting

    2. shading, toning

    3. toning, shading

    4. tinting, shading

    5. tinting, toning

(d)

37. Movement in a positive direction along the C, M, or Y axis represents increasing the amount of incident light that is

    1. reflected

    2. subtracted

(b)

38. Approximately how much time would be required to write an algorithm for converting from CMY to RGB, or from RGB to CMY? (pick the tightest upper bound)

    1. a couple of minutes

    2. less than an hour

    3. less that a day

(a)

39. Where are the pure hues in the HSV hexacone (assume it is “balancing” on the point representing black)?

    1. on the top

    2. on the sides

    3. around the perimeter of the top

    4. on the central axis

    5. on the inside

(c)

40. Continuing the previous question, where are the tints?

    1. on the top

    2. on the sides

    3. around the perimeter of the top

    4. on the central axis

    5. on the inside

(a)

41. Where are the tints in the HLS color model (assume it is “balancing” on the point representing black)

    1. on the outside of the upper cone

    2. on the outside of the lower cone

    3. around the perimeter in the center

    4. on the central axis

    5. on the inside

(a)

42. Which is the following is the LEAST desirable color selection?

    1. uniformly throughout the RGB cube

    2. uniformly along a straight line in the CMY cube

    3. from less than half of the HSV hexacone

    4. (none of the preceding is relatively undesirable)

(a)

43. When a comparison is made between a pinhole camera and raytracing, the “eye” in raytracing corresponds to

    1. a portion of the film plane

    2. the pinhole itself

    3. a point at infinity

(b)

44. Why are rays traced backwards rather than forwards?

    1. fewer rays to trace

    2. light actually travels backwards (for the same reason the lightning originates from the ground and moves toward the clouds)

    3. it’s arbitrary – like driving on the right-hand side of the street

(a)

45. A raytraced scene can suffer from _______ aliasing.

    1. spatial

    2. temporal

    3. (both (a) and (b))

(c)

46. The aliasing problem _____ by supersampling.

    1. can be solved

    2. can be reduced, but not solved

    3. cannot be solved or reduced

(b)

47. A principal advantage of stochastic ray tracing is

    1. minimization of the number of rays which must be traced

    2. its ability to predict which objects will be intersected

    3. elimination of regular aliasing artifacts

    4. viewpoint independence

(c)