Computer Science 455

Instructor: R. P. Burton

Sixth Quiz

April 2-3, 2007

Name _________________________________________ Score ____________/38

1. If halftoning techniques use 3 x 3 pixels for a system in which each of red, green, and blue can be on or off, the number of resultant colors is ____.

   1. unchanged

   2. 3 times as many

   3. 3 x 3 times as many

   4. 3 x 3 x 3 times as many

   5. more than 3 x 3 x 3 times as many

(e)

2. Dithering makes a picture more pleasant by

   1. adding random noise

   2. increasing precision by subpixel calculations

   3. increasing prevision by pixel overlap calculations

(a)

3. Constant surface intensities _____ produce realistic shading.

   1. never

   2. sometimes

   3. always

(b)

4. Where does Gouraud shading first calculate intensities?

   1. at vertices

   2. along edges

   3. across scan lines

(a)

5. The Mach bands which are introduced by Gouraud shading

   1. aren’t really there; the eye and mind produce them

   2. are really present as intensity anomalies as a consequence of Gourand “efficiencies”

(a)

6. An unavoidable disadvantage of Gouraud shading is the irreversible elimination of desirable boundaries, such as between the cheek and lips.

   1. true

   2. false

(b)

7. Where does Phong first calculate intensities?

   1. at vertices

   2. along edges

   3. across scan lines

(c)

8. Suppose rays are sent through pixel centers and the display consists of 1000 x 1000 pixels. What is the maximum number of rays that ultimately can arrive at light sources?

   1. less than 1000 x 1000

   2. exactly 1000 x 1000

   3. more than 1000 x 1000

(c)

9. A disadvantage of an octree representation is the inability to determine surface normals.

   1. true

   2. false

(b)

10. Generally, ray tracing deals with _______ and radiosity deals with _______.

    1. specular intensities, specular intensities

    2. specular intensities, diffuse interreflection

    3. diffuse interreflection, specular intensities

    4. diffuse interreflection, diffuse interreflection

    5. specular intensities and diffuse interreflection, specular intensities and diffuse interreflection

(b)

11. In a radiosity environment, a surface patch

    1. receives illumination

    2. emits illumination

    3. both (a) and (b)

(c)

12. Which of the following is/are done independent of the viewer’s position?

    1. ray tracing

    2. radiosity

    3. both ray tracing and radiosity

    4. neither ray tracing nor radiosity

(b)

13. The visible range of the electromagnetic spectrum consists of only 400,000 (plus or minus a few) discrete colors.

    1. true

    2. false

(b)

14. Where is white light in the visible spectrum?

    1. at the low frequency end

    2. at the high frequency end

    3. in the middle

    4. everywhere

(d)

15. The “color” of a real world object is a collection of the colors it

    1. absorbs

    2. reflects

(b)

16. Which of the following is most “pure” color?

    1. white

    2. pink

    3. red

(c)

17. The “point of diminishing returns” has been passed when the number of primary colors used to determine a color gamut exceeds ____.

    1. 2

    2. 3

    3. 4

    4. (never)

(b)

18. Monitors have red, green and blue phosphors because

    1. they provide the largest color gamut

    2. they represent the extremes of the chromaticity diagram

    3. the eye has peak sensitivity to those colors

    4. they are the least expensive phosphors

(c)

19. Where is the white light position on the chromaticity diagram?

    1. at one of the corners (400 nm or 700 nm)

    2. at the highest point

    3. along the edge, but not at a corner or at the highest point

    4. in the middle

    5. nowhere

(d)

20. Staring with a pure hue and adding white is called

    1. shading

    2. tinting

    3. toning

    4. (any of the above)

(b)

21. Cyan, magenta, and yellow are at corners of the RGB color cube.

    1. true

    2. false

(a)

22. Why is the CMY color model sometimes enhanced to the CMYK color model?

    1. to enlarge the color gamut

    2. to incorporate black

    3. to accommodate transparency

(b)

23. What does “S” stand for in the HSV color model?

    1. shade

    2. saturation

    3. spectrum

(b)

24. Where are all the tints in the HSV color model?

    1. on the inside

    2. on the six outside triangles

    3. on the flat “plateau” opposite the apex

    4. (none of the above)

(c)

25. Where are all the shades in the HSV color model?

    1. on the inside

    2. on the six outside triangles

    3. on the flat “plateau” opposite the apex

    4. (none of the above)

(b)

26. Where are all the tones in the HLS color model?

    1. on the inside

    2. on the outside of the lower code

    3. on the outside of the upper cone

    4. (none of the above)

(a)

27. In general, the greater the number of different colors, the “richer” (in information content) the visual presentation.

    1. true

    2. false

(b)

28. In the computer graphics counterpart of the pinhole camera, what is the pinhole?

    1. the eye

    2. a pixel

(a)

29. Why are rays traced “to” the light source rather than “from” the light source?

    1. to model nature more accurately

    2. to accommodate reflection and refraction

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

    4. to make sure rays pass uniformly through pixels

    5. (all of the above)

(c)

30. How is spatial aliasing overcome (in ray tracing)?

    1. by shooting rays through pixel corners

    2. by distributing rays randomly through pixels

    3. by shooting a sufficient number of rays to achieve homogeneity

    4. (it isn’t)

(d)

31. As might be expected, the most mathematically elegant solution to the ray-object intersection problem also yields the most efficient algorithm.

    1. true

    2. false

(b)

32. Why are glass spheres commonly the “hallmark” of ray-tracing?

    1. because sphere’s are difficult to render accurately using traditional techniques

    2. because refraction is difficult using traditional techniques

    3. because intersurface reflection is difficult using traditional techniques

    4. (all of the above)

(d)

33. For ray-sphere intersection, the ray typically is represented _____ and the sphere typically is represented _____.

    1. explicitly, explicitly

    2. explicitly, parametrically

    3. parametrically, explicitly

    4. parametrically, implicitly

    5. implicitly, parametrically

(d)

34. If a ray intersects a sphere in exactly one point, then the (nonnegative part of the) ray can be assumed be tangent to the sphere at the point of intersection.

    1. true

    2. false

(b)

35. At the point where an extended ray is closest to a sphere’s center, the line from that point to the sphere’s center is perpendicular to the ray.

    1. true

    2. false

(a)

36. Spherical inverse mapping, as discussed in class, takes a point on a sphere and determines a corresponding point in a 2D array.

    1. true

    2. false

(a)

37. Spherical inverse mapping, as discussed in class, _______ distortion.

    1. introduces

    2. does not introduce

(a)

38. The approach taken (in class) to solve the ray-plane intersection problem is fundamentally _______ the approach taken (in class) to solve the ray-sphere intersection problem.

    1. the same as

    2. different from

(a)