Computer
Science 455
Instructor: R. P. Burton
Sixth Quiz
Name
____________________________________ Score
____________/42
1.
Which hidden-element removal algorithms lend
themselves more to zooming in?
a.
object space
b.
image space
c.
neither is superior to the other
for zooming in.
(a)
2.
Coherence, for the purposes of efficiency in
hidden-element removal, refers to
a.
scan lines with runs of constant intensity
b.
patterns which are similar from scan line to scan
line
c.
scenes which are similar from frame to frame
d.
relationships between elements of a scene
e.
(all of the above)
(e)
3.
Which of the following is the simplest piece of
information which is sufficient to do back-face removal? The choices are listed in an order of
decreasing simplicity.
a.
the coordinates of the eye, which can be substituted
into the equation of the plane containing a polygon
b.
the normal vector to a polygon (in viewing
coordinates, of course)
c.
the “C” component of the normal vector
d.
The “z” component of the equation of the plane
containing the polygon.
(c)
4.
In what order are polygons considered (for scan
conversion) by the depth-buffer algorithm?
a.
increasing z_max
b.
decreasing z_max
c.
any order will do
d.
multiple polygons are considered together
(c)
5.
If the depth of a polygon at position (x,y) has been calculated, the depth of the polygon at ____
can be calculated by adding or subtracting a constant.
a.
a pixel with the same x value but a different y
value
b.
a pixel with the same y value, but a different x
value
c.
either (a) or (b)
(c)
6.
In what order are polygons considered (for scan
conversion) by the scan-line algorithm?
a.
increasing z_max
b.
decreasing z_max
c.
any order will do
d.
multiple polygons are considered together
(d)
7.
In determining “spans” to make the scan-line
algorithm more efficient, how many polygons can be “on” simultaneously?
a.
just one
b.
one or two
c.
an unlimited number
(c)
8.
Suppose that the depth-sorting method required two
surfaces (the “subject” and the “neighbor”) to be interchanged. Is it possible that this interchange will
produce a ripple effect, necessitating other interchanges?
a.
no – like selection sort, after the initial sort,
each surface makes exactly one move to its final destination
b.
yes
(b)
9.
Is it possible, after the initial sort in the
depth-sorting method for two surfaces to overlap in x, y, and z, and have it
not be the case that all the vertices of one surface are on one side of the
plane of the other surface?
a.
no
b.
yes
(b
– interpenetration)
10.
Which of the following does NOT terminate the area
subdivision algorithm?
a.
all surfaces are outside the area
b.
only one surface intersects the area, but the
surface is not a surrounder, nor is it completely contained in the area
c.
multiple surfaces intersect the area, but the
closest one surrounds the area
d.
(all of the above terminate subdivision)
(d)
11.
The complexity of the area subdivision algorithm is
related more closely to
a.
the number of subdivisions
b.
the visual complexity of the entire scene
(b)
12.
Any octree can be traversed so that hidden element
removal is performed as information is written (permanently, at least for that
particular frame) to the frame buffer in the order of the traversal.
a.
true
b.
false
(a)
13.
All of the following algorithms can be adapted to,
in effect, perform hidden-line elimination (i.e. produce line drawings with
“hidden” lines removed), EXCEPT
a.
the z-buffer algorithm
b.
the scan-line algorithm
c.
the depth sorting algorithm
d.
the area subdivision algorithm
e.
(no exceptions here)
(e)
14.
The equation for diffuse reflection at a point on a
surface exposed to n point light sources requires _____ ambient component(s)
and ____ point light source component(s).
a.
1,1
b.
1,n
c.
n,1
d.
n,n
(b)
15.
In specular reflection, the intensity falls off
_______ as the angle between the surface normal and the direction of reflection
increases.
a.
linearly
b.
as the cosine of the angle (between the surface
normal and the direction of reflection
c.
neither (a) nor (b), but by amount determined
experimentally that differs from material to material
(c)
16.
The equation for specular reflection contains the
cosine of an angle raised to a power n.
The highlight can be expected to be smaller and brighter when n is a ___
integer.
a.
smaller
b.
larger
(b)
17.
Aside from some of it being reflected, what happens
when light passes obliquely through a flat, uniformly thick pane of glass, such
as a car window?
a.
nothing,
b.
it direction upon exit is different from its
direction upon entrance
c.
it’s path is shifted, but its direction upon exit is
the same as its direction upon entrance
d.
its path is shifted and its direction upon exit is
different from its direction upon entrance
(c)
18.
From the following list of approaches for producing
texture on an orange, pick the entry which either is ineffective or most
inefficient (or both).
a.
micropolygonizing the surface
b.
altering the surface normal as a function of
position
c.
altering the coefficient of reflection as a function
of position
d.
mapping a surface pattern
e.
(none is either effective or relatively inefficient)
(a)
19.
Using hidden surface techniques, if the light can’t
“see” the surface then
a.
the intensity of that surface should not consider
any contribution from that light source
b.
the intensity of that surface should be diminished
by roughly 1/n where n is the number of light sources in the scene
c.
both (a) and (b)
(a)
20.
Suppose each pixel has red, green, and blue
components, each of which can be either “on” or “off.” Suppose a picture is to
made of 3x3 “megapixels.” How many
different colors can a “megapixel” have?
a.
3
b.
8
c.
33
d.
93
e.
93 + 1
f.
103
(f)
21.
Dither noise
a.
can be removed by antialiasing area boundaries
b.
occurs in Gouraud shading, but not in Phong shading
c.
can improve overall appearance
(c)
22.
Several polygons in arbitrary orientations, with a
common coefficient of reflection and illuminated only by ambient light have a
consistent, uniform intensity.
a.
true
b.
false
(a)
23.
Where does Gouraud shading begin failing to model
reality?
a.
in assigning normals to vertices
b.
in calculating intensities only at vertices
c.
in interpolating intensities down edges
d.
in interpolating intensities across scan lines
(b)
24.
Phong is more costly that Gouraud because
a.
Phong considers the sizes of the polygons meeting at
a vertex
b.
Phong does cubic interpolation rather than linear
interpolation
c.
Phong calculates many more dot products
d.
(all of the above)
(c)
25.
If rays are sent through pixel corners rather than
through pixel centers, the number of rays
a.
stays about the same
b.
doubles
c.
four-folds
(a)
26.
Because the faces of octants (in an octree) have
normals facing in positive or negative x, y, or z, normals (or even approximate
normals) can not be determined and hence, octrees are not compatible shading
calculations which use surface normals.
a.
true
b.
false
(b)
27.
If fractal techniques were used to produce the
surface detail for
a.
true
b.
false
(b)
28.
The radiosity model allows patches to
a.
receive and reflect light
b.
emit light
c.
both (a) and (b)
(c)
29.
What is a “form factor” in the radiosity model?
a.
a term describing the orientation of a patch
b.
the faction of energy leaving one patch and arriving
at another
c.
the product of the area of the patch and the
radiosity of the patch
d.
the reflectivity of the patch
(b)
30.
Using the radiosity model, diffuse interreflection
does not need to be determined if
a.
the viewer changes his position
b.
an object in the scene (excluding the viewer)
changes its position
c.
either (a) or (b) occurs
(a)
31.
A “color” such as the color of a shirt, typically is
a.
a pure hue
b.
a pure hue possibly toned
c.
a combination of frequencies
(c)
32.
Suppose the energy of the dominant frequency is
fixed, but the energy of the white light frequencies increases. Which of the following will NOT happen?
a.
the purity of the dominant frequency will diminish
b.
the dominant frequency will be tinted
c.
the dominant frequency will be shaded
d.
(All of the above will happen.)
(c)
33.
What is an optimal, “most rumble for your rupee,”
number of primary colors?
a.
one
b.
two
c.
three
d.
four
e.
more than four
(c)
34.
The “standard primary colors”
a.
are determined by the peak sensitivities of the
cones in the retina
b.
were discovered in 1931 by Roy G. Biv, the famous
British spectromotist
c.
are found in nature (and are manifested in the
rainbow)
d.
were decided upon by a committee and are imaginary
(d)
35.
The primary colors used in most monitors are placed
to maximize coverage of the chromaticity diagram.
a.
true
b.
false
(b)
36.
Given a CMY value, manually determining the
corresponding RGB value requires about as much time as
a.
holding your breath
b.
eating a big slice of pizza
c.
reading a chapter in the graphics book
(a)
37.
In the HSV color model, saturation is related most
closely to
a.
tint
b.
shade
c.
tone
(a)
38.
In the HLS color model, what is along the lightness
axis?
a.
tints
b.
shades
c.
tones
(c)
39.
What is the principal reason for backward ray tracing?
a.
because photons, like electons, are modeled as
flowing “backwards”
b.
because the solid angle associated with the eye is
smaller than the solid angle associated with a light source
c.
because raytracing, historically, is done using
right-handed coordinates
(b)
40.
No matter how many rays are used and no matter how
closely they are packed, small objects or large, far away objects can be
missed.
a.
true
b.
false, provided the scene is supersampled
(a)
41.
What is stochastic ray tracing?
a.
Using several uniformly spaced rays per pixel
b.
Sending out additional rays when adjacent rays
return different colors
c.
Sending out a fixed number of rays, but in random
directions
(c)
42.
The heart (at least one of them) of a ray tracing
package is a set of routines to find the intersection point of a ray and an
object.
a.
true
b.
false
(a)