Does the Quality of the Computer
Graphics Matter When Judging
Distances in Visually Immersive
Environments
William B. Thompson, Peter Willemsen, Amy A. Gooch,
Sarah H. Creem-Regehr, Jack M. Loomis, and Andrew
C. Beall
School of Computing
University of Utah
Outline
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Introduction
Background
Method
Results
Discussion
Introduction



The user’s perception of a virtual world
is important.
Users often perceive objects in virtual
worlds as being smaller than their
intended size.
Does the quality of the rendered image
effect a user’s ability to accurately judge
distances in virtual environments?
Background
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Types of distance perceptions
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Frame of reference
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Egocentric distance
Exocentric distance
Distance Metric
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Absolute distance
Relative distance
Ordinal distance
Background cont.
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Distance from observer to observed
object
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Personal space (arms reach)
Action space (30m)
Vista space (+30m)
Background cont.
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The study in this
paper deals with
absolute egocentric
distance judgments
in action space
Visual Cues for
distance in question
Cue
a
r
o
Accommodation
X
?
?
Binocular Convergence
X
X
X
Binocular Disparity
-
X
X
Linear perspective, height in
picture, horizon ratio
X
X
X
Familiar size
X
X
X
Relative size
-
X
X
Aerial perspective
-
X
X
Absolute motion parallax
?
X
X
Relative motion parallax
-
-
X
Texture gradients
-
X
-
Shading
-
X
-
Occlusion
-
-
X
Related work

Previous Studies
Study
Distances
Real
CG
Task
Witmer and Sadowski (1998)
4.6m – 32m
92%
85%
Treadmill walking
Knapp (1999)
5m – 15m
100%
42%
Triangulated walking
Willemsen and Gooch (2002)
2m – 5m
100%
81%
Direct walking
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Determine the distance, as seen by the
observer, by having the observer
perform some task that is depended on
the perceived distance
Method
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In order to investigate the degree to which image
quality affects distance judgments three distinct styles
of graphic rendering was used.
All computer generated environments were rendered
onSGI Onyx2 R12000 with two IR2 rendering pipelines
Panorama
Low-quality CG
Wireframe
Method cont.
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Panorama
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Multiple images were produced for
different target distances and eye heights.
Two sets of images were taken for each
panorama with the camera offset laterally
to give stereo viewing
Rendering at no less than 40 frames/sec
Method cont.
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Low-quality CG image
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Geometric detail kept simple
Simple point-source lighting
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No shadows
Rendering at no less than 30 frames/sec
Wireframe image
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Feature edges of low-quality image.
Rendering at no less than 40 frames/sec
IMAGE B
IMAGE A
Equipment
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nVision Datavisor HiRes HMD
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Interlaced 1280 x 1024 resolution
Full field sequential color
42° horizontal field of view
2 arc minutes per pixel angular resolution
100% stereo overlap
InterSense IS600 Mark 2 tracker (Head tracker)
Controlling real world cues
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The user’s own body is seldom
rendered in immersive visual
environments
Subjects wore headphones to limit
effects of sound localization
Motion parallax
Procedure
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Subjects were
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Given written instructions
Given a demonstration of the task in space smaller
than the actual experiment spatial layout
Allowed to practice blind walking prior to
experiment
Instructed to get a good image
Allowed to rotate their head about their neck
Not allowed to move their head from side to side
Procedure
target
Direction to
apparent target
Distance to
Target
Direction to
target
≈70º
≈ 2.5m
If the subject turn too
far then they
underestimated
the distance
If the subject does not
turn far enough they
overestimated the
distance
Results
Real world
Panorama
Results cont.
Low-quality CG
Wireframe
Results cont.
Authors claim
Confirmed
previous
that there
studies
is no
showing
that distance
significant
correlation
judgments
between
in the real
world are
image
quality
veryand
accurate
the compression
while
distance
of
the judged
judgments
distance
based on
computer graphics were compressed
Average judged distance as a
percentage of the actual distance
•Panorama ≈ 55%
•Low-quality CG ≈ 44%
•Wireframe ≈ 40%
Discussion
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Authors claim that these results are
strong indicators that the compression
of distance judgments in virtual
environments are NOT caused by a lack
of realistic graphics rendering
“Why can’t I see my reflection in the
glass?”
Possible explanations
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Resolution and sharpness of images in a virtual
environment are limited
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May influence the familiar size effect or degrade the sense of
presence
Motion parallax was not present in the studied virtual
environment
Virtual environments does not give the subject a full
sense of presence
Focus and stereo convergence are not well controlled
in HMDs
Ergonomic effect associated with wearing an HMD
Questions?