Computer Science 455
Instructor: R. P. Burton
Seventh Quiz
June 11-14, 2004
Name _________________________________________ Score ____________/51
1. Which of the following is LEAST appropriate for representing texture?
a. surface micropolygonization
b. dithering
c. messing with surface normals
d. messing with reflection coefficients
e. mapping patterns
(b)
2. How should shadows be computed?
a. By projecting each potential hider onto each potential hidden polygon, diminishing intensity across the projection based on ambient scene illumination.
b. By mapping techniques.
c. By doing nothing; shadows come as a “freebie” with the lighting models discussed in class.
(c)
3. The shadow techniques discussed in class allow for at most one point light source.
a. true
b. false
(b)
4. Halftoning trades
a. resolution for more “colors”
b. processing time for higher resolution
c. storage for realism
(a)
5. Suppose you decide to use “megapixels” which measure 5 x 6, with each conventional pixel having 4 intensity levels (0, 1, 2, and 3). How many intensity levels can each megapixel have?
a. still just 4
b. more than 4, but not more than 10
c. more than 10, but not more than 100
d. more than 100, but not more than 1000
e. more than 1000
(c – 5 x 6 x 3 +1 = 91)
6. Dithering
a. adds noise to produce picture quality
b. micropositions the electron beam
c. interpolates colors between polygons overlapping a common pixel
d. avoids patterns with successively higher grid patterns using preceding pixel sets
(a)
7. Constant intensity (across a polygon surface) is
a. justified only to save computation time
b. sometimes realistic
c. a practice of the past
(b)
8. Gouraud shading overcomes
a. some of the appearance of polygonal boundaries
b. Mach bands
c. Silhouettes which appear polygonal rather than smooth
d. (all of the above)
(a)
9. When _______ shading is used, the boundary between the cheek and the upper lip can remain distinct.
a. Gouraud
b. Phong
c. Gouraud or Phong
(c)
10. Phong shading is _______ Gouraud shading.
a. virtually equivalent to
b. inferior to, but faster than
c. superior to, but slower than
d. superior to, and just as efficient as
(c)
11. In Phong shading, where are intensities calculated for the first time?
a. for each polygon
b. at each vertex
c. along each polygon boundary
d. at each pixel
(d)
12. All of the following occur as a direct consequence of the ray-traced approach EXCEPT
a. hidden surface removal
b. shadows
c. refraction
d. inter-surface reflection
e. view-independent intensity determination
f. (no exceptions here)
(e)
13. A disadvantage of the octree approach is the inability to support the determination (or even estimation) of surface normals.
a. true
b. false
(b)
14. A disadvantage of the “fractal” surfaces produced with the midpoint displacement method is the inability to support the determination (or even estimation) of surface normals.
a. true
b. false
(b)
15. In ray tracing, rays are traced backwards from the eye, into the scene, and (sometimes) back to a light source because
a. like electricity, light actually travels backwards
b. of tradition, mostly, like driving on the right hand side of the road
c. fewer rays need to be traced
d. the distance from the eye to the screen is less that the (typical distance) from a light source to an object in the scene
(c)
16. The boundary between a red polygon and a blue polygon can be made less obvious by a purple band along the boundary.
a. true
b. false
(a)
17. The principal advantage of radiosity is
a. hidden surface removal
b. shadows
c. refraction
d. inter-surface reflection
e. view-independent intensity determination
(e)
18. Given n randomly distributed surface patches, _____ form factors typically are required.
a. roughly n
b. roughly n/2
c. roughly n2/2
d. roughly n2
(c)
19. “The eye can perceive 400,000 distinct colors” means the eye can
a. respond to 400,000 pure hues
b. respond to 400,000 color combinations, some of which are metamers
c. distinguish 400,000 color combinations (but not distinguish metamers)
(a)
20. Where is white light in the visible spectrum?
a. at the low frequency end
b. at the high frequency end
c. right in the middle
d. it involves the whole spectrum
(d)
21. Brightness is determined by
a. relative purity
b. chromaticity
c. the area under the frequency distribution curve
d. the dominant frequency
(c)
22. What is the most efficient number of primary colors?
a. one
b. two
c. three
d. 400,000
(c)
23. What is the source of the standard primary colors?
a. a committee
b. Mother Nature
c. the early work of Roy G Biv
d. the authors of the textbook
e. Ivan E. Sutherland
(a)
24. What is the dimensionality of the chromaticity diagram?
a. one
b. two
c. three
d. four (even thought it is presented in three0
(b)
25. All but one point in the chromaticity diagram can be associated with a pure hue.
a. true
b. false
(a)
26. When an artist adds black and white pigments, she is
a. shading
b. tinting
c. toning
d. desegregating
(c)
27. The red, green, and blue colors in monitors are chosen to
a. match the standard primaries
b. maximize the size of the color gamut
c. provide colors to which the eye has maximum response
d. conform to FCC standards
(c)
28. The primary colors are NOT
a. red, green, and blue
b. red, yellow, and blue
c. cyan, magenta, and yellow
(b)
29. Conversion from RGB to CMY involves
a. subtraction
b. multiplication
c. cross secting
d. integrating
(a)
30. Suppose the HSV hexacone is vertical, balancing on its point. Horizontal movement affects
a. hue
b. saturation
c. value
(b)
31. Continuing the previous question, rotation about the vertical axis affects
a. hue
b. saturation
c. value
(a)
32. Where are the shades in the HLS model?
a. on the inside
b. on the outside
c. in the top half
d. in the bottom half
(b)
33. A good guideline for color selection is to select colors
a. uniformly throughout the RGB or CMY color cube
b. uniformly around the top of the HSV hexacone
c. uniformly along the vertical axis of the HLS cones
d. uniformly from a horizontal cross section of the HSV or HLS models
e. uniformly along a straight line in the RGB or CMY color cube
(e)
34. Unless a ray through a pixel (in ray tracing), or one of its “successors” strikes a light source, the pixel will be black.
a. true
b. false
(a)
35. How is spatial aliasing overcome in ray tracing?
a. by supersampling
b. by stochastic ray tracing
c. by prefiltering
d. by postfiltering
e. (it isn’t overcome – just reduced)
(e)
36. Of the following, the most likely to be ray traced are
a. quadric surfaces
b. fractals
c. octree representations
d. convex hulls
(a)
37. To solve for the intersection of a ray and a sphere, the equation for the ray typically is ______________ and the equation for the sphere is _________.
a. explicit, explicit
b. explicit, implicit
c. implicit, explicit
d. implicit, parametric
e. parametric, implicit
(e)
38. When infinitely extended, a ray always intersects a sphere in at least _____ point(s).
a. 0
b. 1
c. 2
d. 3
(0)
39. For a sphere centered at the origin, what else is needed to find a normal at a known point of intersection on the sphere’s surface?
a. nothing
b. the radius of the sphere
c. the direction of the incident ray
d. the radius of the sphere and the direction of the incident ray
(a)
40. Which of the following can NOT be exploited to increase the efficiency of ray-sphere intersection determination?
a. whether or not the ray originates outside the sphere
b. how close the ray gets to the center of the sphere
c. whether or not the ray points toward the sphere
d. the ray’s direction relative to the normal at the point of intersection
e. (all of the above can be exploited to increase efficiency)
(d)
41. Spherical inverse mapping, as discussed in class, amounts to converting a longitude and a latitude to a position in array, causing the array to be distorted as it is mapped into the sphere.
a. true
b. false
(a)
42. The approach to determining the intersection of a ray and a plane is fundamentally ________ the approach to determining the intersection of a ray and a sphere.
a. the same as
b. different from
(a)
43. Unless a ray and a plane are parallel, a ray will always intersect the plane for some value of t => 0.
a. true
b. false
(b)
44. If a ray intersects a polygon in three-dimensional space, then the projection of the point of intersection will be within a projection of the polygon to two-dimensional space.
a. true
b. false
(a)
45. For purposes of ray/box intersection, the maximum extension of a “slab” is
a. 1
b. the maximum of the width, height, and depth of the scene
c. infinite
(c)
46. Which of the following quadric inverse mappings is likely to introduce the least distortion?
a. cylinder
b. cone
c. ellipsoid
d. paraboloid
e. hyperboloid
f. (all introduce similar distortion)
(a)
47. Which of the following ray/quadric intersections is done fundamentally differently from ray/sphere intersection?
a. cylinder
b. cone
c. ellipsoid
d. paraboloid
e. hyperboloid
f. (none is done fundamentally differently)
(f)
48. Change in direction due to refraction is ________ wavelength.
a. dependent upon
b. independent of
(a)
49. When a photon strikes a surface it is more likely to
a. “bounce” off the surface
b. be absorbed, with another photon emitted subsequently
(b)
50. Total internal reflection ____ accommodated by the ray tracing model.
a. is
b. is not
(a)
51. Why is the highlight on a copper kettle in a store window copper colored?
a. the bronze tinting in the store window
b. the microfacets that make up the copper surface
c. the incident, copper colored light used my the merchant to show off the copper kettle
(b)