Computer Science 455

Instructor: R. P. Burton

Sixth Quiz

April 3-4, 2006

Name _________________________________________ Score ____________/43

1. Texture ______ results from surface contour (height) variations.

   1. always

   2. sometimes

   3. never

(b)

2. Texture can simulated in a computer graphics context by all of the following EXCEPT

   1. micropolygonization of the surface

   2. altering surface normals as a function of position

   3. altering reflection coefficients as a function of position

   4. mapping methods

   5. (no exceptions here)

(e)

3. If object A casts a shadow on object B, it could be said that “Object B is in object A’s shadow.” Therefore, if object B is a cube specified with uniformly colored faces, one face will differ in shade from another face only if there is an object A to cast a shadow on object B.

   1. true

   2. false

(b)

4. Shadows cast on a “solid” surface in n-space are at most n-1-dimensional, even though they may wrap around n-dimensional objects.

   1. true

   2. false

(a)

5. If 1-bit pixels can be either on or off, how many different intensity levels can be presented by 6x6 pixels (one bit each)? (pick the right range)

   1. 1 to 10

   2. 11 to 100

   3. 101 to 1000

   4. 1001 to 10,000

   5. more than 10,000

(b – 37)

6. 6. Continuing the previous question, suppose each pixel has 4 different intensity levels. How many different intensity levels can be presented by 6x6 pixels (one bit each)? (pick the right range)

   1. 1 to 10

   2. 11 to 100

   3. 101 to 1000

   4. 1001 to 10,000

   5. more than 10,000

(c)

7. Dithering

   1. selects from among different pixel patterns with the same intensity

   2. adds noise to improve appearance

   3. removes noise to improve appearance

   4. is synonymous with halftoning

(b)

8. A surface of constant intensity is relatively efficient in terms of processing, but it never results in a realistic image.

   1. true

   2. false

(b)

9. Gouraud shading claims to

   1. eliminate apparent boundaries between surfaces

   2. reduce apparent boundaries between surfaces

   3. eliminate polygonal silhouettes

   4. reduce polygonal silhouettes

   5. (all of the above)

(b)

10. Where does Gouraud first calculate intensities?

    1. at each surface

    2. at each vertex

    3. along each edge

    4. along each scanline

(b)

11. How does Gouraud calculate a normal at a vertex?

    1. he doesn’t

    2. by averaging the normals of the surfaces which meet at the vertex

    3. by averaging the normals of the surfaces which meet at the vertex, weighting each normal according to the area of its associated surface

(b)

12. Gouraud ____ make it possible to preserve a boundary between two adjacent surfaces.

    1. does

    2. does not

(a)

13. 13. Where does Phong first calculate intensities?

    1. at each surface

    2. at each vertex

    3. along each edge

    4. along each scanline

(d)

14. Why are rays traced backwards?

    1. to model the “physics” more accurately (i.e. to capture more accurately how light actually travels)

    2. to make it easier to deal with reflected rays and transmitted rays

    3. to reduce the number of rays that need to be traced

    4. (all of the above)

(c)

15. One of the disadvantages of the octree representation is that it does not lend itself to the calculation (or even the approximation) of surface normals (since all faces are parallel to a principal plane).

    1. true

    2. false

(b)

16. In their basic forms, ray tracing and radiosity deal with

    1. specular reflection and diffuse reflection, respectively

    2. diffuse reflection and specular reflection, respectively

    3. both diffuse and specular reflection

    4. diffuse reflection

    5. specular reflection

(a)

17. The illumination emitted by a “polygon” in a radiosity context is _____ the viewpoint.

    1. heavily dependent on

    2. somewhat dependent on

    3. independent of

(c)

18. 18. One of the disadvantages of the (random midpoint displacement) fractal representation is that it does not lend itself to the calculation of surface normals.

    1. true

    2. false

(b)

19. If, in addition to sending rays through pixel center, rays are sent through pixel corners, the number of rays sent into the scene approximately _____.

    1. stays the same

    2. doubles

    3. four-folds

    4. five-folds

(b)

20. Light, as perceived by our eyes, consists of discrete (as opposed to continuous) frequencies within the electromagnetic spectrum.

    1. true

    2. false

(b)

21. A surface becomes visible when it is struck by a frequency which it does not absorb.

    1. true

    2. false

(a)

22. The combination of reflected frequencies determines a perceived color which is unique to that combination.

    1. true

    2. false

(b)

23. Which is most pure?

    1. white

    2. pink (aka “wee red”)

    3. red

(c)

24. Two colors which combine to produce ____ light are called complementary colors.

    1. white

    2. “black”

    3. ultraviolet

(a)

25. What is the source of the standard primary colors?

    1. seven equally spaced points in the visible spectrum

    2. seven exponentially spaced points in the visible spectrum

    3. the peak retinal response frequencies

    4. a committee

(d)

26. Pick the best statement:

    1. the standard primary colors are at the extrema of the chromaticity diagram

    2. red, green, and blue, as used in screen phosphors, are at the extrema of the chromaticity diagram

    3. both (a) and (b)

    4. neither (a) nor (b)

(d)

27. Where is “white” in the chromaticity diagram?

    1. near the center

    2. on the perimeter

    3. nowhere

    4. everywhere

(a)

28. How many color points are needed to maximize the ratio of i) the percentage of the chromaticity diagram captured to ii) the number of color points used?

    1. two

    2. three

    3. four

    4. ∞

(b)

29. _____ are created by starting with a pure hue and adding black pigment.

    1. Shades

    2. Tints

    3. Tones

(a)

30. Suppose (for each pixel) that red is on or off, green is on or off, and blue is on or off. How many different colors can be achieved using 2x2 pixels?

    1. less than 10

    2. between 11 and 99

    3. between 100 and 999

(c – 125)

31. The primary colors (for Primary-aged children) are

    1. 1, 2, 3

    2. red, yellow and blue

    3. magenta, yellow, and cyan

    4. red, green, and blue

(c)

32. A color and the amounts of black and white are sufficient to make a selection from the HSV model.

    1. true

    2. false

(a)

33. What’s NOT on the outside of the HSV hexacone?

    1. the pure hues

    2. the shades

    3. the tints

    4. the tones

    5. (everything in this list is on the outside)

(d)

34. Colors are likely to “coordinate” if

    1. they represent all subvolumes of the RGB cube and are roughly equally spaced

    2. they are equally spaced and equally distributed on the top of the HSV hexacone

    3. the are selected from extrema of the RGB cube or the HSV hexacone

    4. (none of the above)

(d)

35. A pinhole camera ______ invert the image.

    1. does

    2. does not

(a)

36. A raytraced image _____ invert the scene.

    1. does

    2. does not

(b)

37. Forward ray tracing is

    1. ineffective

    2. inefficient

    3. ineffective and inefficient

    4. effective and inefficient

    5. ineffective but efficient

(d)

38. In a commercial-grade ray tracer, sufficient rays are sent into a pixel so that no object “framed” by the pixel is missed by the ray tracer.

    1. true

    2. false

(b)

39. An object which sometimes is hit (by a ray) and sometimes missed is _______ if the scene consists of at least a few hundred polygons.

    1. consequential

    2. inconsequential

(a)

40. Which of the following “solves” the ray tracing problem (of not missing objects)?

    1. supersampling

    2. adaptive supersampling

    3. stochastic ray tracing

    4. (none of the above)

(d)

41. To solve the ray-sphere intersection problem, the ray is represented _____ and the sphere is represented _____.

    1. explicitly, implicitly

    2. implicitly, explicitly

    3. parametrically, implicitly

    4. implicitly, parametrically

    5. parametrically, explicitly

    6. explicitly, parametrically

(c)

42. If a ray strikes a sphere, it always strikes it in _____ point(s).

    1. one

    2. two (though the two points may be the same)

    3. two (and the two points are always distinct)

(a)

43. The surface normal (at a point where a ray strikes a sphere) always points away from the center of the sphere.

    1. true

    2. false

(b)