Computer Science 455
Instructor: R. P. Burton
Sixth Quiz
March 29-30, 2004
Name _________________________________________ Score ____________/xx
1. Assuming that the contents of an octree are represented in world coordinates (or some linearly scaled version of world coordinates), projection for presentation is most likely to be
a. parallel orthographic
b. parallel oblique
c. perspective orthographic
d. perspective oblique
e. whatever the user chooses
(a)
2. Which of the following algorithms lends itself least to hidden-line elimination?
a. depth buffer
b. scan-line
c. depth sorting
d. area subdivision
e. octree
(e)
3. Given a collection of vertices, edges, and polygons, how can you determine if they were determined by measurement, by sweeping, by constructive solid geometry techniques, or by random midpoint displacement techniques?
a. it is implicit in the geometry
b. it is implicit in the topology
c. it is explicit in the geometry
d. it is explicit in the topology
e. in general you can’t
(e)
4. Diffuse reflection represents less net energy reflection than specular reflection.
a. true
b. false
(b)
5. The intensity of point source light reflected from a diffuse surface ______ the angle of the incident illumination.
a. depends on
b. is independent of
(a)
6. The color of a specular reflection is
a. usually determined predominantly by the color of the incident light
b. usually determined predominantly by the properties of the surface
c. white
(a)
7. In a specular reflection, the intensity falls off ____________.
a. linearly with the angle of incidence
b. as the cosine of the angle of incidence
c. neither (a) nor (b), but as a function of the surface material and the angle of incidence
(c)
8. The direction of a light ray exiting a medium with parallel sides (such as a slab of glass) is _______ the direction of the light ray entering the medium.
a. co-linear with
b. parallel to, but not co-linear with
c. different from
(b)
9. Texture can be achieved efficiently by all of the following EXCEPT
a. micropolygonization of the surface
b. altering the surface normal as a function of position
c. altering the reflection coefficient as a function of position
d. using texture mapping methods
e. (no exceptions here)
(a)
10. Efficiently applied texture causes the appearance (size and position) of the shadows cast by the surface upon itself to change as the position of the light source changes.
a. true
b. false
(b)
11. What is a shadow polyhedron?
a. a polyhedron that casts a shadow
b. a polyhedron that receives a shadow
c. (either (a) or (b))
d. A polyhedron formed by a surface that can “see” a light source and the projection of that surface to the far plane.
(d)
12. A “super pixel” (which is actually n x m conventional pixels, each of which can be on or off) can have ____ different intensity levels.
a. 2
b. max (n,m)
c. n + m
d. n x m
e. n x m –1
f. n x m + 1
(f)
13. Continuing the previous question, how does the number of intensity levels change if each pixel has p different intensity levels?
a. it doesn’t change
b. it’s multiplied by p
c. it’s multiplied by something slightly less than p
d. it’s multiplied by something slightly more than p
(c – p x n x m + 1)
14. What’s the purpose of dithering?
a. to delay transition
b. to remove noise to make the picture more accurate
c. to add noise to make the picture more appear more accurate
d. to move from a lower dimension to a higher dimension
(c)
15. Constant intensity:
a. It’s only advantage is that it is relatively efficient to render
b. In some cases, it produces realistic shading
(b)
16. What becomes of the polygonal silhouette of a Gouraud-shaded polyhedron?
a. it remains polygonal
b. it is smoothed, but careful inspection suggests the locations of vertices
c. it is smoother, and even careful inspection does not suggest the locations of vertices
(a)
17. Where is the point in the following list at which Gouraud shading considers normals for the last time?
a. for individual planes
b. at vertices
c. along edges, at each edge/scan-line intersection
d. along scan lines, at each pixel
(b)
18. Where is the point in the following list at which Phong shading considers normals for the last time?
a. for individual planes
b. at vertices
c. along edges, at each edge/scan-line intersection
d. along scan lines, at each pixel
(d)
19. Suppose rays are shot into a scene through the center of each pixel in a 1000 x 1000 display. Rays terminate when they exit the scene, when they strike a light source, or after they have struck a finite number of objects (doing whatever they do when they strike the object). How many total rays probe the scene (where one “ray” we mean a single polyline)?
a. 1000 x 1000
b. 1000 x 1000 x 4
c. a theoretically unlimited number
(c)
20. When a scene is represented by an octree, it is impossible to determine (or even estimate) the orientation of the surface represented in the octree.
a. true
b. false
(b)
21. If fractal techniques are used to produce an element of a scene, it is impossible to determine (or even estimate) the orientation of the surface represented by the fractal.
a. true
b. false
(b)
22. For antialiasing purposes, suppose rays are shot through the corner of each pixel instead of through each pixel center. How does this change the total number of rays sent into the scene?
a. No change at all
b. Not much change
c. It doubles the number
d. It quadruples the number
e. It more than quadruples the number
(b)
23. Which of the following is an advantage that radiosity has over raytracing?
a. It’s much faster than ray tracing, and produces almost indistinguishable results.
b. It presents the results of both ambient light and point source light.
c. It determines illumination in a view-independent manner.
d. It allows surfaces (not just light sources) to emit illumination.
(c)
24. There are approximately _____ pure hues visible to the human eye.
a. 7
b. 70
c. 700
d. 7000
e. 70,000
f. (substantially more than 70,000)
(f – 400,000)
25. The combination of _____ frequencies determines the perceived color of an object.
a. absorbed
b. reflected
(b)
26. Which of the following is the most pure hue?
a. black
b. white
c. red
(c)