Specular Reflection and
Usability of Tablet PCs
My
eyes!
Nooooo!
It
burns!
John Gore
COMP 7700
Spring 2006
Outline
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Introduction
Specular Reflection
Experiment Design
Demonstration
Results
Conclusions
Introduction
The purpose of this study is to test the
effects of Specular Reflection on Tablet PC…
• Reading Speed
• Input Speed
• Usability
This study was performed
by Auburn Engineers
(www.auburnengineers.com)
Specular Reflection
Specular Reflection occurs when light bounces off a smooth
surface into an observer’s eyes. For this to occur, the angle
between the observer’s eyes and the surface and the light
source and surface must be the same.
How can we avoid specular reflection? Change the
geometric relationship.
•Tilt the Tablet
•Change Posture
•Move Light Source
Experiment – Conditions
• Display Quality
• Narrow vs. Wide: Type of filter
used on the Tablet PC screen
• Low Ambient vs. High Ambient
light: 30 foot-candles or 105 footcandles
• High Reflectivity vs. Low
Reflectivity: Type of Tablet PC
screen cover
• Tilt Angle: 0, 30, 45, 60 degrees
Experiment – Tests
• Chapman-Cook Speed of Reading Test
• Given a passage such as “There was a fire
last night and five houses burned to the
ground. It all happened because someone
was careless and threw a nail into the
waste-paper basket,” pick the inconsistent
word
• 6 passages per test
• 4 options per passage
Experiment – Tests
• Target Tap Test
• Based off of Fitts’ law and ISO input
testing specifications
• 4 circles of varying radiuses
• 6 sequential targets positioned along
the circumference of each circle
• Targets separated by 190 degrees
Experiment – Tests
• Questionnaire
• 7 point Likert scale
• Strongly Agree to Strongly Disagree
• 7 Questions such as “I can quickly tap targets
with the stylus when using the Tablet PC”
• Interview
• “Is tilt condition X acceptable?”
• “Rank the tilt conditions in order of
preference”
• “Do you prefer Wide or Narrow?”
Demonstration
Results – Display Quality
Speed of Reading Test
• Best overall condition: Narrow, Low
Ambient, Low Reflectivity
• Breakdown by conditions
• Narrow vs. Wide
• High Ambient vs. Low Ambient
• High Reflectivity vs. Low Reflectivity
Results – Display Quality
Display Quality - Reading Test
43.0
42.0
Avg sec/test
41.0
40.0
39.0
38.0
37.0
36.0
Narrow
Wide
High Amb
Low Amb
Condition
High Reflect
Low Reflect
Results – Display Quality
Target Tap Test
• Best Condition: Wide, High
Ambient, Low Reflective
• Breakdown by conditions
• Narrow vs. Wide
• High Ambient vs. Low Ambient
• High Reflectivity vs. Low Reflectivity
Results – Display Quality
Display Quality - Tap Test
1.13
1.12
Avg sec/target
1.11
1.10
1.09
1.08
1.07
1.06
Narrow
Wide
High Amb
Low Amb
Condition
High Reflect
Low Reflect
Results – Tilt Angle
Tilt Angle - Reading Test
Tilt Angle - Tap Test
48.0
1.35
46.0
1.30
Avg sec/target
Avg sec/test
44.0
42.0
40.0
1.25
1.20
38.0
1.15
36.0
1.10
34.0
0
30
45
Angle
60
0
30
45
Angle
60
Results – Questionnaire
• No two subjects agreed on an
optimum tilt angle.
• All subjects preferred Wide over
Narrow and no Reflective cover
(High vs. Low Reflectivity)
Results – Tilt Angle Rankings
Angle
Acceptable
0
5
30
7
45
10
60
4
Angle
0
30
45
60
Preferred
1
4
3
2
Results – Questionnaire
Display Quality - Likert Scale
110.0
105.0
100.0
Points
95.0
90.0
85.0
80.0
75.0
70.0
Narrow
Wide
High Amb
Low Amb
Condition
High Reflect
Low Reflect
Results - Questionnaire
Tilt Angle - Likert Scale
34.0
32.0
Points
30.0
28.0
26.0
24.0
22.0
0
30
45
Condition
60
Conclusions
• Perceived comfort and usability is a
combination of many factors, weighted
differently for each candidate. A larger
subject pool is necessary to make any
definitive statement about which conditions
are most important
• Users always prefer a Wide filter and a Low
Reflectivity surface.
• In general, a 45 degree tilt angle +/- 15
degrees is preferred.
• Based on the test data, 45 degrees is
optimum for both reading and input tasks.
Questions?