Asai K. (ed.) Human-Computer Interaction. New Developments
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A Touchscreen Software Keyboard for Finger Typing
291
and adaptable keyboards; and (2) they can be designed to display the visual feedback of
they keys and on the keys.
Our approach to designing touchscreen keyboards is to address the weak points using
customizable and adaptable functions and effective visual feedback to improve their
perceived usability. We designate the method as Customizable and Adaptable Touchscreen
Keyboard with Bubble Cursor-Like Visual Feedback: CATKey (Go & Endo, 2007).
3.2 Customizable Key Layout
Figure 2 portrays the concept of Voronoi key area of our keyboard design. Figure 2(a)
depicts a typical QWERTY layout keyboard, consisting of rectangular keys. Figure 2(b) is the
initial key layout of our CATKey. Each key has a maximum area; consequently, the overall
key area forms a Voronoi diagram (Aurenhammer, 1991). Himberg et al. (2003) employ this
approach for an onscreen numeric 10-key pad. In the keyboard, each key consists of a set of
points.
V
i
= { x | d(x, c
i
) < d(x, c
j
), for all j ≠ i }
(1)
In that equation, x is the coordinate of a point, d is the Euclidean distance, and c signifies the
coordinate of the key centroid.
Q W E R T Y U I O P
A S D F G H J K L
Z X C V B N M
SPACE
Q W E R T Y U I O P
A S D F G H J K L
Z X C V B N M
SPACE
QWERTYU IOP
ASDFGHJKL
ZXCVBNM
SPACE
QWERTYU IOP
ASDFGHJKL
ZXCVBNM
SPACE
(a) QWERTY layout of rectangular keys (b) QWERTY layout of keys with Voronoi
area
Fig. 2. The Voronoi key area concept
Figure 3 presents a key layout customized by a user in the customization mode of CATKey.
In this mode, the user adjusts each key by touching and manipulating it directly so that the
user feels that the layout is easy to use. The customized key area also forms a Voronoi
diagram.
Q
W
ER
T
Y
U
I
O
P
A
S
D
F
G
H
J
K
L
Z
X
C
V
B
N
M
SPACE
Q
W
ER
T
Y
U
I
O
P
A
S
D
F
G
H
J
K
L
Z
X
C
V
B
N
M
SPACE
Fig. 3. A key layout customized by a user
Human-Computer Interaction, New Developments
292
3.3 Adaptable Keys
We designed an adaptable function similar to that presented by Himberg et al. (2003). In the
adaptive mode of CATKey, the key centroid is moved to the centroid of recorded keystroke
points in each key (Fig. 4). The keystroke coordinates are recorded for the period of the pre-
specified number of keystrokes.
(a) Original key area (b) User’s typing
points (X-mark)
(c) Recalculated
centroid of the
typing points
(d) Adjusted key
area
Fig. 4. The key adaptation mechanism of CATKey: Black point, the original centroid. X-
mark: keystroke points; White circle, the centroid of the keystroke points and the weighted
original centroid; Dotted line, recalculated key area.
3.4 Visual Feedback
Figure 5 depicts the design of visual feedback in CATKey. Figure 5(a) portrays an actual
view of CATKey. We assigned a round key area to communicate the touched location to the
user. The yellow f and j keys show home positions of the index fingers. The presence of the
line and color of keys can be modified using the parameter-setting dialogue.
Figure 5(b) shows the bubble cursor-like visual feedback (Grossman & Balakrishnan, 2005).
The bubble-shaped cursor in red adjusts dynamically to the closest key and provides the
sensation of an offset cursor (Sears & Shneiderman, 1991). Figure 6 presents the concept of
bubble cursor-like visual feedback used in CATKey. Figure 6(a) shows the Voronoi area of a
key that has a colored circle with the centroid as its middle. It redraws the circle in a
different color as visual feedback when the user touches inside the color circle (Fig. 6(b)).
When the user touches outside the color circle, it redraws the circle in a different color,
draws a circle with its keystroke point as its middle, and merges them (Fig. 6(c)). The radius
of the second circle is the distance from user’s keystroke point to the color circle.
(a) Overview of CATKey with lines and color circles (b) Bubble cursor-like visual
feedback
Fig. 5. Design of visual feedback in CATKey
A Touchscreen Software Keyboard for Finger Typing
293
(a) Color circle (b) User’s keystroke point
is in the color circle
(c) User’s keystroke point
is outside the color circle
Fig. 6. Concept of bubble cursor-like visual feedback: Black point, the centroid of the key;
Dotted line, the inscribed circle of the key; X-mark, keystroke point.
4. Evaluation of CATKey
We evaluated the usability of CATKey based on ISO 9241-4 (1998). We measured the text
entry speed and error rate using a hardware QWERTY keyboard, a software QWERTY
keyboard, and CATKey, and assessed its comfort; finally, we conducted a debriefing
interview.
Ten college students (two women and eight men) participated in the evaluation. Each uses a
hardware QWERTY keyboard regularly, but seldom uses a touchscreen keyboard for daily
activities.
A CAD Center NEXTRAX 15 touchscreen computer was used for evaluation. It has a 15-inch
TFT monitor with 1024 × 768-pixel resolution. Also, CATKey was implemented using C#
(Visual Studio.Net 2003; Microsoft Corp.). Figure 7 shows a user typing with NEXTRAX 15,
which has a 20-deg mounting angle. For hardware keyboards, standard QWERTY
keyboards (Dell Computer Corp.) were used. The sentences were chosen randomly from
among pangrams such as “a quick brown fox jumps over the lazy dog,” “how quickly daft
jumping zebras vex,” and “pack my box with five dozen liquor jugs.”
Fig. 7. Experimental setting (NEXTRAX 15).
Each experimental session included 10 sentences for the typing task. Each participant
performed two practice sessions, then completed four sessions for measurement. The
presentation order of keyboard types was counterbalanced.
Human-Computer Interaction, New Developments
294
Results indicate that the respective mean entry speeds of the hardware QWERTY keyboard,
software QWERTY keyboard, and CATKey were 33.5, 23.8, and 22.8 wpm. A significant
difference was found among the keyboards (F(2, 18) = 7.5, p<0.05); but no significant
difference was found between the levels of the software QWERTY keyboard and CATKey.
Similarly, the respective mean error rates of the hardware QWERTY keyboard, software
QWERTY keyboard, and CATKey were 3.4, 5.9, and 6.8%. A significant difference was
found among the keyboards (F(2, 18) = 6.3 (p<0.05)); but no significant difference was found
between the levels of software QWERTY keyboard and CATKey. Furthermore, no
significant difference was found from the assessment of comfort between the software
QWERTY keyboard and CATKey.
5. Conclusion
In this chapter, we examined the criteria of touchscreen keyboard text entry. We specifically
emphasized the use of a touchscreen keyboard use for finger typing. We analyzed it from
five aspects: screen size, touchscreen keyboard types, number of keys, typing device, and
technique.
Additionally, we described the CATKey design: it is a customizable and adaptable
touchscreen keyboard with the bubble cursor-like visual feedback. Our criteria suggest that
CATKey is better used for medium or larger touchscreen devices. Incorporating a soft
keyboard approach, it has alphabetical keys. It specifically examines finger typing, but is
useful for a stylus also. Although it has no prediction function, its keyboard layout can be
customized. It has an adaptation function. Finally, its visual appearance has a bubble cursor-
like visual feedback.
Early results of evaluation show that the mean text entry speed and mean input error rate of
CATKey are not significantly different from those of a standard software QWERTY
keyboard. This result might indicate limitations of our design: users need a compelling
reason to replace their text entry device from a static standard QWERTY keyboard from a
performance viewpoint. Notwithstanding, during the debriefing interview, the participants
expressed their preference for the design and usability of CATKey.
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16
Structured Light Illumination Methods for
continuous motion hand and face-computer
interaction
Charles J. Casey, Laurence G. Hassebrook and Daniel L. Lau
University of Kentucky
Department of Electrical and Computer Engineering
Lexington, Kentucky
USA
1. Introduction
Traditionally, human-computer interaction (HCI) has been facilitated by the use of physical
input devices. However, as the use of computers becomes more widespread and
applications become increasingly diverse, the need for new methods of control becomes
more pressing. Advances in computational power and image capture technology have
allowed the development of video-based interaction. Existing systems have proven
themselves useful for situations in which physical manipulation of a computer input device
is impossible or impractical, and can restore a level of computer accessibility to the disabled
(Betke et al., 2002). The next logical step is to further develop the abilities of video-based
interaction. In this chapter, we consider the introduction of third dimensional data into the
video-based control paradigm. The inclusion of depth information can allow enhanced
feature detection ability and greatly increase the range of options for interactivity. Three-
dimensional control information can be collected in various ways such as stereo-vision and
time-of-flight ranging. Our group specializes in Structured Light Illumination of objects in
motion and believe that its advantages are simplicity, reduced cost, and accuracy. So we
consider only the method of data acquisition via structured light illumination.
Implementation of such a system requires only a single camera and illumination source in
conjunction with a single processing computer, and can easily be constructed from readily
available commodity parts. In following sections, we will explain the concept of 3D HCI
using structured light, show examples of facial expression capture and demonstrate an
example of a “3D virtual computer mouse” using only a human hand.
2. Structured Light Illumination
Structured light illumination (SLI) allows one to measure the depth information of a surface
by measuring the deformation in a projected light pattern (Schmaltz, 1932). A simple
example would be a pattern of stripes projected onto a sphere. When viewed obliquely, the
light stripes on the sphere appear curved as shown in Fig. 1. For a given arrangement of the
298 Human-Computer Interaction, New Developments
projector and camera, the variation in a pattern can be characterized extremely accurately,
such that a precise model of the surface can be reconstructed. Most modern
implementations of SLI systems make use of digital projectors to illuminate the subject and
a digital camera to capture an image of the illuminated subject, though in certain cases static
projection devices (slide projectors, for example) may be used.
Fig. 1. (left) SLI geometry and (right) example stripe pattern on sphere.
Mathematically, the SLI measurement process is based on triangulation. Accurate results
can be produced only when there is a well defined relationship between a single point on
the projection plane and the corresponding point on the captured image, as shown in Fig. 1.
It is to establish this relationship that projection patterns are utilized. A projection pattern
(or more frequently a series of patterns) is designed such that each pixel (or row or column,
depending on the specific implementation) of the projection image is uniquely
characterized, either by some characteristic intensity value sequence or by some other
identifiable property such as a local pattern of shapes or colors. When projected onto a
subject, the captured image (or series of images) can be analyzed to locate these identifiable
projection pattern points. Given a fixed placement of camera and projector, the location of
any given pattern point on the subject creates a unique triangle with dimensions defined by
the depth of the subject surface.
A well designed projection pattern can achieve significant accuracy and precision (Li et al.,
2003). However, due to the difficulties involved in encoding each pixel uniquely, many of
the most effective pattern types require more than one projection/capture instance in order
to reconstruct the subject surface. These are known as time-multiplexed patterns. For
example, the Phase Modulation Profilometry (PMP) (also known as sine wave shifting)
technique utilizes a series of patterns in the form of sinusoidal grayscale gradient images,
each shifted by a certain phase angle. Varying the intensity in this way will encode each
row (or column) in the projector with a unique phase value. However, it has been shown
that the accuracy of the phase value (and thus, the measurement of subject depth) is
dependent on the number of shifts used. Therefore, a more accurate surface reconstruction
requires more pattern projections and thus a longer scanning process.
Structured Light Illumination Methods for continuous motion hand and face-computer interaction 299
2.1 Structured Light Illumination Motion Capture Methods
For many scanning applications it would be ideal to capture the required surface
information in only a single projection/image instance. This is because during a multiple
pattern scan, subject motion introduces error into the depth measurement. These techniques
are therefore largely problematic for motion capture and human interaction. Fortunately,
there are other options for single frame SLI capture, which offer not only reduced scan time,
but also allow one to scan a moving subject. Most single pattern techniques fall into two
categories; color-multiplexed types and neighborhood-search types.
Color-multiplexing simply combines individual patterns from some multi-pattern technique
into a single pattern by coloring each differently. A three pattern PMP sequence, for
example, can easily be combined into a single pattern by coloring each of the three patterns
red, green, or blue. In this way, each pattern can be isolated independently of the others by
considering only the R, G, or B channel of the captured image. Each channel image is
effectively identical to a single frame of the corresponding multi-pattern PMP scan process.
While the concept is simple, the number of patterns that can be combined in this way is
usually relatively limited and analysis is plagued by non-idealities (Pan et al., 2006). In
addition, color patterns introduce a strong dependence on subject coloration and luminance
properties. If a subject is strongly colored blue, for example, there may be insufficient
information in the R and G image channels to properly reconstruct the surface.
Neighborhood-search methods take a different approach entirely. These techniques utilize a
pattern (usually binary in nature, that is, black and white colors only) in which subsections
of the pattern can be uniquely identified in some way. Specific implementations may utilize
patterns of noise or streaks (Maruyama & Abe, 1993) in which a point can be identified
according to the known local statistical characteristics of the pattern, or deterministic sub-
patterns defined by M-arrays or De Bruijn binary sequences (Morita et al., 1988) (Hall-Holt
& Rusinkiewicz, 2001) wherein the identity of one point can be determined by the
information contained in nearby points. Like color-multiplexed systems, the accuracy of
neighborhood-search based techniques may be strongly dependent on subject surface
characteristics. If pieces of the pattern can be obscured by subject features or distorted too
much by local gradients, correct identification of the pattern points may be impossible. In
addition, the primarily binary nature of the patterns can limit the resolution possible. Thus,
only a small portion of surface points may be measured.
There are other methods of motion capture based on entirely different concepts. One
method is to utilize high-speed hardware to simply run multi-pattern sequences faster
(Zhang & Huang, 2006) reducing the effect that the subject’s movement has on the depth
measurement to a negligible amount. The composite pattern technique (Guan et al., 2003)
combines component patterns of a time multiplexed method, such as PMP, into a single
pattern by modulating each by a known frequency. This allows an effect similar to that of
color-multiplexing, but avoids many of its drawbacks. Another new method, Lock and
Hold (Hassebrook & Lau, 2006), utilizes a multi-pattern scan followed by a continuously
projected tracking pattern (the Hold pattern) in order to scan moving subjects. The latter
two options advantageously require no specialized hardware.
300 Human-Computer Interaction, New Developments
2.2 Composite Pattern
SLI systems frequently utilize patterns that vary only in a single direction (the “phase
direction”, a term taken from PMP and “y
p
” in Fig. 1) and are constant in the other (the
“orthogonal direction” or “x
p
” in Fig. 1). In such a system, the camera is offset from the
projector along the phase axis only. In this way, depth variation will cause variation in the
pattern along the phase direction while leaving the pattern unaltered in the orthogonal
direction. To visualize the effect, consider a square projected onto the surface of a sphere. If
one views the sphere from an offset parallel to one set of sides of the square, these sides will
still appear straight, while the other sides will appear curved. Composite Pattern
multiplexing takes advantage of this fact by introducing sinusoidal variation along the
orthogonal direction. When a surface illuminated with a composite pattern is viewed by the
camera, the modulating signal will be unaltered by the surface features and can be used to
isolate the component patterns in a way analogous to isolating each channel in an RGB
color-multiplexed image.
Consider a four pattern PMP sequence. The intensity of each of the four patterns varies
sinusoidally along the phase direction only. To combine the four into a single pattern, each
is element-wise multiplied by a modulating image; patterns which vary sinusoidally in the
orthogonal direction only, each at a unique (relatively high) frequency, as shown in Fig. 2.
The modulated patterns are combined (and the resulting intensity scaled as necessary for
the projection device) to create the composite pattern.
Fig. 2. Composite Pattern combining 4 PMP patterns into a single composite pattern.
When a composite pattern is used to illuminate a subject, the captured image must be
processed in order to extract the original component PMP pattern images. These images can
then be analyzed as though they were individual frames in a multi-pattern scan sequence.
The process of isolating the component images is very similar to the process of isolating
modulated communications channels. Considering the 2D Fourier transform of the image,
component pattern information will appear as four signal envelopes shifted in the
orthogonal direction by the modulating frequencies. Each pair of these envelopes
(considering both positive and negative frequencies) is isolated using 2D band-pass filters.
The inverse Fourier transform of these isolated bands are the equivalent component pattern
images, and are then used to determine the surface depth according to standard PMP