Computer Science 455
Instructor: R. P. Burton
Sixth Quiz
November 24-25, 2003
Name
_________________________________________ Score
____________/50
1.
Suppose a scene to be ray traced consists of a pyramid, a cylinder, and
a light source. What guarantees that a
ray through a particular pixel will bounce off one of the surfaces and strike
the light source?
a.
nothing
b.
because the positions of the objects and the light source are known,
the surface normal is ignored and the reflected ray is directed either toward another
object or toward the light source
c.
Rays are sent through each pixel at several different angles until one
of the rays strikes an object AND reaches a light source.
(a)
2.
The color of a particular pixel can be determined by more than one
(poly)ray making its way from a light source back to
the view plane.
a.
true
b.
false
(a
– with partially transparent surfaces)
3.
Suppose than an object (maybe a brain or other internal organ) is
represented in an octree. Since the
faces of the octants all have normals parallel to the x, y, or z axis, no
surface normal can be calculated or even estimated.
a.
true
b.
false
(b)
4.
Suppose a fractal surface is generated by random midpoint
displacement. How is the resulting
surface different from a surface consisting of several polygonal patches?
a.
it isn’t different
b.
such a fractal surface has no conventional (or even approximate) normal
c.
such a fractal surface could not be smooth-shaded
(a)
5.
Suppose rays are sent through pixel corners instead of through pixel
centers. As a consequence, the number of
rays approximately
a.
stays the same
b.
doubles
c.
quadruples
(a)
6.
A primary advantage of radiosity is
a.
smoothing of polygonally approximated surfaces without a need for
explicit smooth-shading techniques
b.
calculation of intersurface reflection without having to trace rays (or
anything like rays)
c.
calculation of scene illumination in a view-independent manner
(c)
7.
Suppose a scene (to which radiosity is to be applied) consists of 1000
surface patches. Of those, what is the
maximum number than can contribute to the “radiosity” or any particular surface
patch?
a.
just one
b.
500
c.
999
d.
1000
(d)
8.
Pick the best statement:
a.
the eye can respond to approximately 4,000,000 distinct frequencies
b.
the eye can distinguish approximately 4,000,000 distinct frequencies
c.
the eye can respond to approximately 400,000 distinct frequencies
d.
the eye can distinguish approximately 400,000 distinct frequencies
e.
the eye can respond to approximately 40,000 distinct frequencies
f.
the eye can distinguish approximately 40,000 distinct frequencies
(c)
9.
How many pure hues are there?
a.
3
b.
7
c.
64
d.
more than 1,000
(d)
10.
A common set of primary colors includes
a.
1, 2, 3
b.
red, yellow, blue
c.
magenta, yellow, and cyan
d.
(any of the above is correct)
(c)
11.
The “point of diminishing returns” is reached (i.e. the ratio between
the number of primary colors and the number of colors captured in the color
gamut begins to diminish) when the number of primary colors exceeds
a.
two
b.
three
c.
four
d.
sixteen
(b)
12.
What is the source of the “standard primaries”?
a.
the cones in the retina
b.
the sun
c.
a committee
(c)
13.
Some of the standard primaries are “imaginary.”
a.
true
b.
false
(a)
14.
The three primary colors are represented in a chromaticity diagram of
____ dimensions.
a.
two
b.
three
c.
four
(a)
15.
Every point in the chromaticity diagram, except the white light
position, is unambiguously associated with a dominant frequency.
a.
true
b.
false
(a)
16.
If someone adds grey pigment to a pure color, they are
a.
shading
b.
tinting
c.
toning
(c)
17.
The visual pigments in the retina have peak sensitivities at the
“extremes” (i.e. vertices or apexes) of the chromaticity diagram.
a.
true
b.
false
(b)
18.
Cyan, magenta, and yellow are at vertices of the RGB color cube.
a.
true
b.
false
(a)
19.
The conversion from RGB to CMY is as complicated as
a.
addition or subtraction
b.
multiplication or division
c.
cross-secting
d.
finding a suboctant in an octree
(a)
20.
Where are the greys in the HSV hexacone?
a.
on the flat, hexagonal “top”
b.
right down the “middle” (from the center of the “top” to the “point”)
c.
around the perimeter of the “top”
d.
down an “edge” along the outside
e.
down a “face” along the outside
(b)
21.
The HLS color model is closest to the _____ color model.
a.
RGB
b.
CMY
c.
HSV
d.
FYI
e.
QED
(c)
22.
Which of the following is the worst
approach to color selection, for aesthetic
purposes?
a.
points distributed uniformly throughout the RGB or CMY cube
b.
points distributed uniformly along a straight line in the RGB or CMY
cube
c.
points restricted to not more than half of the HSV hexacone
(a)
23.
Which of the following would be least
suitable for presentation representaton using
a particle system?
a.
fire
b.
grass
c.
waterfalls
d.
molecules
(d)
24.
The techniques and principles which undergird physically-based modellingmodeling
are
a.
easily understood and incorporated, once the techniques
and principles of computer graphics are understood.
b.
, as a group, about as difficult to understand and incorporate as are
visual surface determination techniques and principles
c.
challenging and demanding, requiring to typical practitioner to focus
on a small subset of tasks
(c)
25.
To what, in ray tracing, does the pinhole in a pinhole camera
correspond?
a.
a pixel on the image plane
b.
the center of the image plane
c.
the viewpoint
(c)
26.
Ray tracing is naturally suited for
a.
specular reflection and transmission
b.
diffuse reflection and transmission
c.
both (a) and (b)
(a)
27.
How is antialiasing solved in ray tracing?
a.
by supersampling
b.
by adaptive supersampling
c.
by stochastic ray tracing
d.
by statistical supersampling
e.
(it is not solved; merely reduced)
(e)
28.
A principal advantage of stochastic (aka “distributed”) ray tracing is
a.
reduction of the likelihood of missing small objects
b.
elimination of regular aliasing artifacts
c.
fewer rays per pixel
d.
(all of the above)
(b)
29.
The mathematical elegance is directly related to the efficiency with
which a ray tracing technique executes.
a.
true
b.
false
(b)
30.
A ray is sent into a scene consisting of 100 spheres. Which sphere will the ray strike first
(which intersection will be computed first)?
a.
the one with the smallest z-value
b.
the largest one
c.
the one it’s neighbor struck
d.
who knows?!
(d)
31.
A ray is sent into a scene consisting of 100 spheres. The ray must be tested individually for
intersection with every one of these spheres, i.e. 100 ray-sphere intersections
tests must be conducted if the scene is to be ray-traced correctly.
a.
true
b.
false
(b)
32.
Continuing the previous question...the ray should be represented _____
and the sphere should be represented ______
a.
parametrically, parametrically
b.
explicitly, explicitly
c.
implicitly, implicitly
d.
parametrically, explicitly
e.
parametrically, implicitly
f.
explicitly, implicitly
(e)
33.
A ray and a sphere will intersect at ____ unique real
points. (Pick the most complete answer.)
a.
0 or 2
b.
0, 1, or 2
c.
2
(b)
34.
Suppose your calculations show that a ray and a sphere intersect at a
complex point, i.e. a point with a real and an imaginary component. What do you conclude?
a.
you made an error in your calculations
b.
the ray emanates inside the sphere
c.
the ray does not intersect the sphere
(c)
35.
Given the center and radius of a sphere, and given the origin and
direction of a ray which intersects the sphere, the normal (to the sphere) at
the point of intersection can be calculated without requiring additional
information.
a.
true
b.
false
(a)
36.
Which of the following is NOT a potential advantage of the geometric
solution (to the ray-sphere intersection problem) relative to the algebraic
solution?
a.
predetermination of the need to calculate just one root
b.
predetermination of no need to calculate any roots
c.
(both (a) and (b) are relative advantages)
(c)
37.
For the geometric solution to the ray-sphere intersection problem, how
is the ray represented?
a.
explicitly
b.
implicitly
c.
parametrically
(c)
38.
Spherical inverse mapping amounts to determining a longitude and a latitude, which can be mapped to a 2D array of color or
texture.
a.
true
b.
false
(a)
39.
For purposes of spherical inverse mapping, which of the following
is/are needed?
a.
the point of intersection of the ray and the sphere
b.
the normal at the point of intersection of the ray and the sphere
c.
(both (a) and (b) are needed)
(b)
40.
For purposes of spherical inverse mapping, which of the following
is/are NOT needed?
a.
the location of the center of the sphere
b.
the radius of the sphere
c.
a vector from the center of the sphere through its “north pole”
d.
a vector from the center of the sphere through some point in its
“equator”
e.
(all are needed)
(b)
41.
Ray-plane intersection puts the ray & plane in the same forms,
respectively, as ray-sphere intersection puts the ray & sphere.
a.
true
b.
false
(a)
42.
Which of the following predeterminations LEAST improves the efficiency
of ray-plane intersection?
a.
determining if the ray and plane are parallel
b.
determining if the ray points away from the plane
c.
determining if the plane points away from the ray
(c)
43.
Suppose a ray intersects the plane 3x – 4y +
2z + 5 =0. For purposes of determining
if a particular triangle in this plane is intersected, the triangle and
intersection point should be projected to the ____ plane.
a.
xy
b.
yz
c.
zx
(c)
44.
Aside from determining the intersection of a ray and a polygon (which
lies in a plane), there is no practical application in ray tracing which
requires the determination of a value of the parameter t where a ray intersects
a plane.
a.
true
b.
false
(b)
45. Suppose that (for a particular ray-box intersection), for the x-slab, t-near is 1.0 and t-far is 10.0; for the y-slab, t-near is 0.5 and t-far is 3.5; for the z-slab, t-near is 5.5 and t-fat is 11.5. After determining the final values for t-near and t-far, what is (t-far – t-near), i.e. the difference between t-near and t far?
a.
negative
b.
zero
c.
between zero and five
d.
between five and ten
e.
greater than ten
(a)
45.
Continuing the previous question, does the ray intersect the box?
a.
yes
b.
no
(b)
46.
For determining the intersection of a ray with a quadric, what kind of
equation is solved (i.e. how many roots are there)?
a.
linear (1)
b.
quadratic (2)
c.
cubic (3)
d.
quartic (4)
(b)
47.
The mapping to a ____ is likely to introduce the least distortion of
the original quadrilateral?
a.
circle
b.
cylinder
c.
cone
d.
(all introduce roughly equivalent distortion)
(b)
48.
Which is the more accurate statement?
When photons strike a surface
a.
the frequencies not represented in the surface are absorbed and the
photons, less these frequencies, “bounce” off the surface
b.
the photons are absorbed by the surface, the atoms in the surface move
to a higher energy level, the atoms shed the energy, and new photons are
generated/emitted from the surface
(b)
49.
The index of refraction depends on the ____ and the angle of refraction
depends on the ____.
a.
medium, medium
b.
medium, wavelength of the incoming light
c.
wavelength of the incoming light, medium
d.
wavelength of the incoming light, wavelength of the incoming light
(b)
50.
White light striking a shiny copper kettle produces a highlight which
is
a.
white
b.
copper colored
(b)