U.S. patent application number 11/764723 was filed with the patent office on 2008-03-20 for apparatus for detecting a pointer within a region of interest.
This patent application is currently assigned to SMART Technologies Inc.. Invention is credited to Patrick James Gurtler, Gerald D. Morrison, Stephen Worthington.
Application Number | 20080068352 11/764723 |
Document ID | / |
Family ID | 34838199 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080068352 |
Kind Code |
A1 |
Worthington; Stephen ; et
al. |
March 20, 2008 |
APPARATUS FOR DETECTING A POINTER WITHIN A REGION OF INTEREST
Abstract
An apparatus for detecting a pointer within a region of interest
includes at least one pair of imaging devices. The imaging devices
have overlapping fields of view encompassing the region of
interest. At least one light source provides illumination across
the region of interest and is within the field of view of at least
one of the imaging device. A filter is associated with the at least
one imaging device whose field of view sees the light source. The
filter blocks light projected by the light source to inhibit the
imaging device from being blinded by the projected light.
Inventors: |
Worthington; Stephen;
(Calgary, CA) ; Morrison; Gerald D.; (Calgary,
CA) ; Gurtler; Patrick James; (Calgary, CA) |
Correspondence
Address: |
PATENT ADMINISTRATOR;KATTEN MUCHIN ROSENMAN LLP
1025 THOMAS JEFFERSON STREET, N.W.
EAST LOBBY: SUITE 700
WASHINGTON
DC
20007-5201
US
|
Assignee: |
SMART Technologies Inc.
Suite 600 1177 - 11th Avenue S.W.
Calgary
CA
T2R 1K9
|
Family ID: |
34838199 |
Appl. No.: |
11/764723 |
Filed: |
June 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10778534 |
Feb 17, 2004 |
7232986 |
|
|
11764723 |
Jun 18, 2007 |
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Current U.S.
Class: |
345/175 |
Current CPC
Class: |
G06F 3/0421 20130101;
G02B 5/124 20130101 |
Class at
Publication: |
345/175 |
International
Class: |
G06F 3/042 20060101
G06F003/042 |
Claims
1-44. (canceled)
45. An apparatus for detecting a pointer within a region of
interest comprising: at least one pair of imaging devices, said
imaging devices having overlapping fields of view encompassing said
region of interest; at least one light source providing
illumination across said region of interest and being within the
field of view of at least one of said imaging devices; and an
optical filter associated with the at least one imaging device
whose field of view sees said light source, said filter blocking
light projected by said light source to inhibit said imaging device
from being blinded by said projected light.
46. An apparatus according to claim 45 wherein said filter blocks
light having a characteristic different from a characteristic
assigned to the at least one imaging device.
47. An apparatus according to claim 46 wherein said characteristic
includes at least one of polarization and frequency.
48. An apparatus according to claim 46 including a light source
associated with each imaging device, each light source being in the
field of view of the non-associated imaging device, light projected
by each light source being visible to said associated imaging
device and being blocked by a filter associated with the
non-associated imaging device.
49. An apparatus according to claim 48 wherein said characteristic
includes at least one of polarization and frequency.
50. An apparatus according to claim 49 wherein the light source
associated with one imaging device projects illumination having a
first polarization orientation and wherein the light source
associated with the other imaging device projects illumination
having a second polarization orientation.
51. An apparatus according to claim 50 wherein the first and second
polarization orientations are vertical and horizontal polarization
orientations.
52. An apparatus according to claim 46 wherein said region of
interest overlies a touch surface on which pointer contacts are
made.
53. An apparatus according to claim 52 wherein said touch surface
and region of interest are rectangular.
54. An apparatus according to claim 53 including a light source
associated with each imaging device, each light source being in the
field of view of the non-associated imaging device, light projected
by each light source being visible to said associated imaging
device and being blocked by an optical filter associated with the
non-associated imaging device.
55. An apparatus according to claim 54 wherein said characteristic
includes at least one of polarization and frequency.
56. An apparatus according to claim 55 wherein the light source
associated with one imaging device projects illumination having a
first polarization orientation and wherein the light source
associated with the other imaging device projects illumination
having a second polarization orientation.
57. An apparatus according to claim 56 wherein the first and second
polarization orientations are vertical and horizontal polarization
orientations.
58. An apparatus for detecting a pointer within a region of
interest comprising: at least one pair of imaging devices, said
imaging devices having overlapping fields of view looking generally
across said region of interest; a light source associated with each
imaging device, each said light source providing illumination
across said region of interest and being in the field of view of
the non-associated imaging device; an optical filter device
associated with each imaging device so that substantially only
light projected by the light source associated therewith is
received by said associated imaging device to avoid the imaging
device from being blinded by other light; and a filter device
associated with each light source to alter a characteristic of
projected light such that the projected light is unable to pass
through the filter device associated with the non-associated
imaging device.
59. An apparatus according to claim 58 wherein said filter devices
are polarizers.
60. An apparatus according to claim 59 wherein each light source is
an infrared light source.
61. An apparatus according to claim 60 wherein each infrared light
source includes at least one infrared light emitting diode (IR
LED).
62. An apparatus according to claim 58 further comprising:
retro-reflective elements bordering said region of interest, said
retro-reflective elements returning light impinging thereon in the
direction of impingement without altering the polarization
thereof.
63. An apparatus according to claim 58 wherein said region of
interest overlies a touch surface on which pointer contacts are
made.
64. An apparatus according to claim 63 wherein said touch surface
and region of interest are rectangular.
65. An apparatus according to claim 64 wherein said filter devices
are polarizers.
66. An apparatus according to claim 65 including an imaging device
and associated light source at each corner of said region of
interest, diagonally opposite imaging devices being aimed generally
at one another.
67. An apparatus according to claim 66 wherein one of the
diagonally opposite polarizers has a vertical orientation and
wherein the other of the diagonally opposite polarizers has a
horizontal orientation.
68. An apparatus for detecting a pointer within a region of
interest comprising: an imaging device adjacent at least two
corners of said region of interest, the imaging devices having
overlapping fields of view looking generally across said region of
interest from different viewpoints, each imaging device having a
different optical filter associated therewith so that each imaging
device substantially only captures light having a particular
characteristic thereby to avoid being blinded by light not having
said particular characteristic; and a light source associated with
each imaging device, each said light source projecting light across
said region of interest having a particular characteristic such
that the projected light only passes through the optical filter of
said associated imaging device.
69. An apparatus according to claim 68 wherein each light source is
an infrared light source.
70. An apparatus according to claim 69 wherein each infrared light
source includes at least one infrared light emitting diode (IR
LED).
71. An apparatus according to claim 68 wherein said region of
interest overlies a touch surface on which pointer contacts are
made.
72. An apparatus according to claim 71 wherein said touch surface
and region of interest are rectangular.
73. An apparatus according to claim 72 wherein said imaging devices
are configured to capture light having different polarizations.
74. An apparatus according to claim 73 wherein said different
polarizations are vertical and horizontal.
75. An apparatus for detecting a pointer within a region of
interest comprising: at least two color imaging devices having
overlapping fields of view looking generally across said region of
interest; processing circuitry receiving and processing images
acquired by said imaging devices to determine the location of said
pointer relative to said region of interest; and at least one
illumination source projecting light in a specified frequency range
across said region of interest thereby to provide lighting for said
imaging devices, wherein said color imaging devices are sensitive
to ambient light to capture color images and are sensitive to the
light projected by said at least one illumination source to capture
monochrome images.
76. An apparatus according to claim 75 wherein said illumination
source is operated to project light when ambient light levels fall
below a threshold level.
77. An apparatus according to claim 76 wherein said illumination
source projects light in the infrared range.
78. An apparatus according to claim 75 said illumination source
projects light in the infrared range.
79. An apparatus according to claim 78 wherein said region of
interest overlies a touch surface.
80. An apparatus according to claim 79 wherein said illumination
source is operated to project light when ambient light levels fall
below a threshold level.
81. An apparatus according to claim 75 wherein said region of
interest overlies a touch surface.
82. An apparatus for detecting a pointer contact on a generally
rectangular touch surface comprising: a color imaging device at
each corner of said touch surface and having a field of view
looking generally across said touch surface; processing circuitry
receiving and processing images acquired by said imaging devices to
determine the location of said pointer relative to said region of
interest; and illumination sources surrounding said touch surface
and projecting light in a specified frequency range across said
touch surface thereby to provide backlighting for said imaging
devices, wherein said color imaging devices are sensitive to
ambient light to capture color images and are sensitive to the
light projected by said illumination sources to capture monochrome
images.
83. An apparatus according to claim 82 wherein said illumination
sources are operated to project light when ambient light levels
fall below a threshold level.
84. An apparatus according to claim 83 wherein said illumination
sources project light in the infrared range.
85. An apparatus for detecting a pointer within a region of
interest comprising: at least two monochrome imaging devices having
overlapping fields of view looking generally across said region of
interest; processing circuitry receiving and processing images
acquired by said imaging devices to determine the location of said
pointer relative to said region of interest; at least one
illumination source projecting light across said region of
interest; and at least one filter changing the frequency band of
light in a cycle thereby to enable said imaging devices to capture
images looking across said region of interest in different lighting
conditions.
86. An apparatus according to claim 85 wherein said illumination
source projects light of different frequencies across said region
of interest in a repeating cycle.
87. An apparatus according to claim 86 wherein said illumination
source projects infrared, red, blue, and green light in a cycle
across said region of interest.
88. An apparatus for detecting a pointer within a region of
interest comprising: at least one pair of imaging devices, said
imaging devices having overlapping fields of view looking generally
across said region of interest; a light source associated with each
imaging device, each said light source providing illumination
across said region of interest and being in the field of view of
the non-associated imaging device; and a different optical filter
device associated with each imaging device so that substantially
only light projected by the light source associated therewith is
received by said associated imaging device to avoid the imaging
device from being blinded by other light.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to interactive
systems and in particular to an apparatus for detecting a pointer
within a region of interest.
BACKGROUND OF THE INVENTION
[0002] Touch systems are well known in the art and typically
include a touch screen having a touch surface on which contacts are
made using a pointer such as for example a pen tool, finger or
other suitable object. Pointer contacts with the touch surface are
detected and are used to generate output pointer position data
representing areas of the touch surface where pointer contacts are
made.
[0003] International PCT Application No. PCT/CA01/00980 filed on
Jul. 5, 2001 and published under number WO 02/03316 on Jan. 10,
2002, assigned to SMART Technologies Inc., assignee of the present
invention, discloses a passive camera-based touch system. The
camera-based touch system comprises a touch screen that includes a
touch surface on which a computer-generated image is presented. A
rectangular bezel or frame surrounds the touch surface and supports
digital cameras at its corners. The digital cameras have
overlapping fields of view that encompass and look across the touch
surface. The digital cameras acquire images of the touch surface
from different locations and generate image data. The image data is
processed by digital signal processors to determine if a pointer
exists in the captured image data. When it is determined that a
pointer exists in the captured image data, the digital signal
processors convey pointer characteristic data to a master
controller, which in turn processes the pointer characteristic data
to determine the location of the pointer in (x,y) coordinates
relative to the touch surface using triangulation. The pointer
location data is conveyed to a computer executing one or more
application programs. The computer uses the pointer location data
to update the computer-generated image that is presented on the
touch surface. Pointer contacts on the touch surface can therefore
be recorded as writing or drawing or used to control execution of
an application program executed by the computer.
[0004] Although this camera-based touch system works extremely
well, it has been found that when the digital camera frame rates
are high, in less favorable light conditions, the ability to
determine the existence of a pointer in the captured image data is
diminished. As a result, there exists a need to improve the
lighting environment for the digital cameras to ensure high
resolution irrespective of ambient lighting conditions.
[0005] U.S. patent application Ser. No. 10/354,168 to Akift et al.
entitled "Illuminated Bezel And Touch System Incorporating The
Same", assigned to SMART Technologies Inc., assignee of the present
invention, discloses an illuminated bezel for use in the
above-described camera-based touch system. The illuminated bezel
projects infrared backlighting across the touch surface that is
visible to the digital cameras. As a result, when no pointer is
positioned within the fields of view of the digital cameras, the
digital cameras see bright bands of illumination as a result of the
projected backlighting. When a pointer is positioned within the
fields of view of the digital cameras, the pointer occludes the
backlight illumination. Therefore, in each captured image the
pointer appears as a high-contrast dark region interrupting the
bright band of illumination allowing the existence of the pointer
in the captured image to be readily detected.
[0006] Although the illuminated bezel works very well, because the
illuminated bezel completely surrounds the touch surface and makes
use of an array of infrared light emitting diodes mounted on a
printed circuit board that is disposed behind a diffuser,
manufacturing costs are significant especially in cases where the
illuminated bezel surrounds large touch surfaces. As will be
appreciated, lower cost backlight illumination for touch systems of
this nature is desired.
[0007] Also, although the existence of the pointer in captured
images can be readily detected, currently the use of monochrome
digital cameras to capture images increases costs and provides
limited information concerning attributes of the pointer used to
contact the touch system.
[0008] It is therefore an object of the present invention to
provide a novel apparatus for detecting a pointer within a region
of interest.
SUMMARY OF THE INVENTION
[0009] Accordingly, in one aspect of the present invention, there
is provided an apparatus for detecting a pointer within a region of
interest comprising:
[0010] at least one pair of imaging devices, said imaging devices
having overlapping fields of view encompassing said region of
interest;
[0011] at least one light source providing illumination across said
region of interest and being within the field of view of at least
one of said imaging devices; and
[0012] a filter associated with the at least one imaging device
whose field of view sees said light source, said filter blocking
light projected by said light source to inhibit said imaging device
from being blinded by said projected light
[0013] In one embodiment, the filter blocks light having a
characteristic different from a characteristic assigned to the at
least one imaging device. The characteristic may be one of
polarization and frequency. The apparatus may include a light
source associated with each imaging device, with each light source
being in the field of view of the non-associated imaging device.
Light projected by each light source is visible to its associated
imaging device but is blocked by the filter associated with the
non-associated imaging device.
[0014] The region of interest may overlie a touch surface on which
pointer contacts are made, with imaging devices and associated
light sources being provided adjacent each corner of the touch
surface.
[0015] According to another aspect of the present invention there
is provided an apparatus for detecting a pointer within a region of
interest comprising:
[0016] at least one pair of imaging devices, said imaging devices
having overlapping fields of view looking generally across said
region of interest;
[0017] a light source associated with each imaging device, each
said light source providing illumination across said region of
interest and being in the field of view of the non-associated
imaging device; and
[0018] a filter device associated with each imaging device so that
substantially only light projected by the light source associated
therewith is received by said associated imagining device.
[0019] According to still yet another aspect of the present
invention there is provided an apparatus for detecting a pointer
within a region of interest comprising:
[0020] an imaging device adjacent at least two corners of said
region of interest, the imaging devices having overlapping fields
of view looking generally across said region of interest, said
imaging devices being configured to capture light having a
particular characteristic; and
[0021] a light source associated with each imaging device, each
said light source projecting light across said region of interest
having a characteristic of the type capturable by said associated
imaging device.
[0022] According to still yet another aspect of the present
invention there is provided an apparatus for detecting a pointer
within a region of interest comprising:
[0023] at least two color imaging devices having overlapping fields
of view looking generally across said region of interest;
[0024] processing circuitry receiving and processing images
acquired by said imaging devices to detect the existence of a
pointer in said images and to determine the location of said
pointer relative to said region of interest; and
[0025] at least one illumination source projecting light in a
specified frequency range across said region of interest thereby to
provide lighting for said imaging devices, wherein said color
imaging devices are sensitive to ambient light to capture color
images and are sensitive to the light projected by said at least
one illumination source to capture monochrome images.
[0026] According to still yet another aspect of the present
invention there is provided an apparatus for detecting a pointer
contact on a generally rectangular touch surface comprising:
[0027] a color imaging device at each corner of said touch surface
and having a field of view looking generally across said touch
surface;
[0028] processing circuitry receiving and processing images
acquired by said imaging devices to detect the existence of a
pointer in said images and to determine the location of said
pointer relative to said region of interest; and
[0029] illumination sources surrounding said touch surface and
projecting light in a specified frequency range across said touch
surface thereby to provide backlighting for said imaging devices,
wherein said color imaging devices are sensitive to ambient light
to capture color images and are sensitive to the light projected by
said illumination sources to capture monochrome images.
[0030] According to still yet another aspect of the present
invention there is provided an apparatus for detecting a pointer
within a region of interest comprising:
[0031] at least two monochrome imaging devices having overlapping
fields of view looking generally across said region of
interest;
[0032] processing circuitry receiving and processing images
acquired by said imaging devices to detect the existence of a
pointer in said images and to determine the location of said
pointer relative to said region of interest; and
[0033] at least one illumination source projecting light across
said region of interest; and
[0034] at least one filter changing the frequency band of light in
a cycle thereby to enable said imaging devices to capture images
looking across said region of interest in different lighting
conditions.
[0035] The present invention provides advantages in that in one
embodiment, backlight illumination is provided across the touch
surface in an effective and cost efficient manner. The present
invention provides further advantages in that since images looking
across the region of interest can be acquired at different
frequency bands of light, in addition to determining the location
of the pointer, increased pointer attribute information can be
easily obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Embodiments of the present invention will now be described
more fully with reference to the accompanying drawings in
which:
[0037] FIG. 1 is a schematic diagram of an apparatus for detecting
a pointer within a region of interest;
[0038] FIG. 2 is a front elevation view of a touch screen forming
part of the apparatus of FIG. 1;
[0039] FIG. 3 is another front elevation view of the touch screen
of FIG. 2;
[0040] FIG. 4 is a schematic diagram of a digital camera forming
part of the touch screen of FIG. 2;
[0041] FIG. 5 is a schematic diagram of a master controller forming
part of the apparatus of FIG. 1;
[0042] FIG. 6 is a front elevational view of an alternative
embodiment of the touch screen;
[0043] FIG. 7 is a front elevational view of yet another embodiment
of the touch screen; and
[0044] FIG. 8 is a graph showing the light sensitivity of digital
cameras used in the touch screen of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0045] Turning now to FIGS. 1 to 3, an apparatus for detecting a
pointer within a region of interest in accordance with the present
invention is shown and is generally identified by reference numeral
50. In this embodiment, apparatus 50 is a camera-based touch system
similar to that disclosed in International PCT Application Serial
No. WO 02/03316, assigned to SMART Technologies Inc., assignee of
the present invention, the content of which is incorporated herein
by reference. As can be seen, touch system 50 includes a touch
screen 52 coupled to a digital signal processor (DSP) based master
controller 54. Master controller 54 is also coupled to a computer
56. Computer 56 executes one or more application programs and
generates computer-generated image output that is presented on the
touch screen 52. The touch screen 52, master controller 54 and
computer 56 form a closed-loop so that pointer contacts made on the
touch screen 52 can be recorded as writing or drawing or used to
control execution of an application programs executed by the
computer 56.
[0046] FIGS. 2 and 3 better illustrate the touch screen 52. Touch
screen 52 in the present embodiment includes a high-resolution
display device such as a plasma display 58, the front surface of
which defines a touch surface 60. The touch surface 60 is bordered
by a bezel or frame 62 coupled to the display device. Corner pieces
68 that house DSP-based CMOS digital cameras 70 are located at each
corner of the bezel 62. Each digital camera 70 is mounted within
its respective corner piece 68 so that its field of view
encompasses and looks generally across the entire plane of the
touch surface 60.
[0047] An infrared light source 72 is associated with and
positioned adjacent each-digital camera 70. Each light source 72
includes an array of infrared (IR) light emitting diodes (LEDs).
The light emitting diodes project infrared lighting across the
touch surface 60.
[0048] Polarizers 74 are provided in front of the digital cameras
70 and the infrared light sources 72. The polarization of the
polarizers 74 at opposite corners of the touch surface 60 have
opposite polarization. For example, in this embodiment, the
polarizers 74 at the top and bottom left corners of the touch
surface 60 have a vertical orientation and the polarizers 74 at the
top and bottom right corners of the touch surface 60 have a
horizontal orientation. In this manner, the polarizers 74 minimize
the light projected by the diagonally opposite infrared light
sources 72 that is seen by the digital cameras 70 i.e. block the
diagonally opposite infrared light sources 72 from their fields of
view thereby to avoid digital camera photo-saturation and other
effects that reduce the effectiveness of the digital cameras
70.
[0049] One of the digital cameras 70 within a corner piece 68 is
shown in FIG. 4. As can be seen, the digital camera 70 includes a
two-dimensional CMOS image sensor and associated lens assembly 80,
a first-in-first-out (FIFO) buffer 82 coupled to the image sensor
and lens assembly 80 by a data bus and a digital signal processor
(DSP) 84 coupled to the FIFO 82 by a data bus and to the image
sensor and lens assembly 80 by a control bus. A boot EPROM 86 and a
power supply subsystem 88 are also included. In the present
embodiment, the CMOS camera image sensor is configured for a
20.times.640 pixel subarray that can be operated to capture image
frames at high frame rates in excess of 200 frames per second since
arbitrary pixel rows can be selected. Also, since the pixel rows
can be arbitrarily selected, the pixel subarray can be exposed for
a greater duration for a given digital camera frame rate allowing
for good operation in dark rooms as well as well lit rooms.
[0050] The DSP 84 provides control information to the image sensor
and lens assembly 80 via the control bus. The control information
allows the DSP 84 to control parameters of the image sensor and
lens assembly 80 such as exposure, gain, array configuration, reset
and initialization. The DSP 84 also provides clock signals to the
image sensor and lens assembly 80 to control the frame rate of the
image sensor and lens assembly 80.
[0051] An infrared pass filter 89 is provided on the image sensor
and lens assembly 80 to blind the digital camera 70 to frequencies
of light outside the infrared range.
[0052] Master controller 54 is better illustrated in FIG. 5 and
includes a DSP 90, a boot EPROM 92, a serial line driver 94 and a
power supply subsystem 95. The DSP 90 communicates with the DSPs 84
of the digital cameras 70 over a data bus via a serial port 96 and
communicates with the computer 56 over a data bus via a serial port
98 and the serial line driver 94.
[0053] The master controller 54 and each digital camera 70 follow a
communication protocol that enables bidirectional communications
via a common serial cable similar to a universal serial bus (USB).
Communications between the master controller 54 and the digital
cameras 70 are performed as background processes in response to
interrupts.
[0054] The operation of the touch system 50 will now be described.
To provide appropriate lighting for the digital cameras 70, the
infrared light source 72 associated with each digital camera 70
generates infrared light that is projected across the touch surface
60 covering an area at least as large as the field of view of the
associated digital camera.
[0055] As mentioned previously, the polarizers 74 at opposite
diagonal corners of the touch surface 60 inhibit the infrared light
source 72 diagonally opposite each digital camera 70 from blinding
that digital camera due to the different polarization orientations
of the polarizers 74. Infrared light impinging on a polarizer 74
that is polarized in a manner different from the polarization
orientation of the polarizer is blocked. In this manner, the
digital camera 70 behind each polarizer 74 in effect does not see
the infrared light source 72 at the diagonally opposite corner.
[0056] Each digital camera 70 acquires images looking across the
touch surface 60 within the field of view of its image sensor and
lens assembly 80 at a desired frame rate and processes each
acquired image to determine if a pointer is in the acquired image.
When a pointer is positioned within the fields of view of the
digital cameras 70, the pointer is illuminated by the light
projected by the infrared light sources 72. Light reflecting off of
the pointer typically does not maintain its polarization and
therefore is visible to the digital cameras 70. Therefore, the
illuminated pointer appears as a high-contrast bright region
interrupting a dark band in each captured image allowing the
existence of the pointer in the captured images to be readily
detected.
[0057] If a pointer is in the acquired image, the image is further
processed to determine characteristics of the pointer contacting or
hovering above the touch surface 60. Pointer information packets
(PIPs) including pointer characteristics, status and/or diagnostic
information are then generated by the digital cameras 70 and the
PIPs are queued for transmission to the master controller 54.
[0058] The master controller 54 polls the digital cameras 70 for
PIPs. If the PIPs include pointer characteristic information, the
master controller 54 triangulates pointer characteristics in the
PIPs to determine the position of the pointer relative to the touch
surface 60 in Cartesian rectangular coordinates. The master
controller 54 in turn transmits calculated pointer position data,
status and/or diagnostic information to the computer 56. In this
manner, the pointer position data transmitted to the computer 56
can be recorded as writing or drawing or can be used to control
execution of an applications program executed by the computer 56.
The computer 56 also updates the computer-generated image output
conveyed to the plasma display 58 so that information presented on
the touch surface 60 reflects the pointer activity.
[0059] Specifics concerning the processing of acquired images and
the triangulation of pointer characteristics in PIPs are described
in U.S. patent application Ser. No. 10/294,917 to Morrison et al.,
assigned to SMART Technologies Inc., assignee of the present
invention, the content of which is incorporated herein by
reference. Accordingly, specifics will not be described further
herein.
[0060] As will be appreciated, the use of infrared light sources 72
and polarizers 74 at the corners of the touch surface 60 inhibit
light sources in the fields of view of the digital cameras from
blinding the digital cameras.
[0061] Turning now to FIG. 6, another embodiment of a touch screen
is shown and is generally identified by reference numeral 152.
Tough screen 152 is similar to that of the previous embodiment but
in this case the bezel 162 is designed to allow the touch screen
152 to operate in an occlusion mode. As can be seen, bezel 162, in
this embodiment, includes elongate retro-reflectors 164 bordering
the sides of the touch surface 160. The retro-reflectors 164 have
retro-reflecting surfaces 166 lying in planes that are generally
normal to the plane of the touch surface 160.
[0062] The retro-reflectors 164 are designed to maintain
polarization of light impinging thereon. In the present embodiment,
corner cube retroreflectors such as those manufactured by Reflexite
Corporation and sold under the name Reflexite.TM. AP1000 that
preserve polarization are used.
[0063] In this embodiment, when infrared light generated by the
infrared light sources 172 travels across the touch surface and
impinges on one or more retro-reflectors 164, the retro-reflectors
164 in turn reflect the infrared light back in the opposite
direction while maintaining the polarization of the infrared light.
Since the infrared light sources 172 are mounted adjacent the
digital cameras 170, infrared light reflected by the
retro-reflectors 164 is aimed back towards the digital cameras 170.
As a result, each digital camera 170 sees a bright band of
illumination within its field of view.
[0064] During image acquisition, when no pointer is positioned
within the fields of view of the digital cameras 170, the digital
cameras 170 see bright bands of illumination. When a pointer is
positioned within the fields of view of the digital cameras 170,
the pointer occludes the infrared illumination and therefore
appears as a high-contrast dark region interrupting a bright band
of illumination in each captured image allowing the existence of
the pointer in the captured images to be readily detected.
[0065] The embodiments of the touch screen described above show
digital cameras, infrared light sources and polarizers at each
corner of the touch screen. Those of skill in the art will
appreciate that only two imaging devices having overlapping fields
of view are required. Also the infrared light sources need not be
positioned adjacent the digital cameras. In addition other types of
filters may be used to inhibit the digital cameras from being
blinded by a light source within its field of view. Basically any
filter type device that blocks light projected by a light source
within the field of view of the digital camera based on a
characteristic (i.e. polarization, frequency etc.) of the projected
light may be used.
[0066] In addition, although each light source is described as
including an array of IR LEDs, those of skill in the art will
appreciate that other light source configurations to provide light
illumination across the touch surface can be used.
[0067] Although the touch system 50 has been described as including
a plasma display 58 to present images on the touch surface, those
of skill in the art will appreciate that this is not required. The
touch screen may be a rear or front projection display device or
virtually any surface on which a computer generated image is
projected. Alternatively, the touch system 50 may be a writeboard
where images are not projected on the touch surface.
[0068] Also, although the touch system 50 is described as including
a master controller 54 separate from the digital cameras, if
desired one of the digital cameras can be conditioned to function
as both a camera and the master controller and poll the other
digital cameras for PIPs. In this case, the digital camera
functioning as the master controller may include a faster DSP 84
than the remaining digital cameras.
[0069] Turning now to FIG. 7, yet another embodiment of a touch
screen is shown and is generally identified by reference numeral
252. In this embodiment, touch screen 252 includes a
high-resolution display device such as a plasma display 258, the
front surface of which defines a touch surface 260. The touch
surface 260 is bordered by an illuminated bezel or frame 262
coupled to the display device. Illuminated bezel 262 is of the type
disclosed in U.S. patent application Ser. No. 10/354,168 to Akitt
et al., assigned to SMART Technologies Inc., assignee of the
present invention, the content of which is incorporated by
reference. Illuminated bezel 262 includes elongate side frame
assemblies 264 that are coupled to the sides of the plasma display
258. Each side frame assembly 264 accommodates a generally
continuous infrared illumination source 266. The ends of the side
frame assemblies 264 are joined by corner pieces 268 that house
DSP-based CMOS digital cameras 270. Each digital camera 270 is
mounted within its respective corner piece 268 so that its field of
view encompasses and looks generally across the entire touch
surface 260.
[0070] Each illuminated bezel 262 includes an array of IR LEDs (not
shown) that project light onto a diffuser (not shown). The diffuser
in turn, diffuses and expands the infrared light emitted by the IR
LEDs so that adequate infrared backlighting is projected across the
touch surface 260. As a result, the illuminated bezels 162 appear
as generally continuous bright bands of illumination to the digital
cameras 270.
[0071] Rather than using monochrome digital cameras capturing
infrared images, in this embodiment, the image sensors used in the
digital cameras 270 are color CMOS image sensors and do not include
IR pass filters. FIG. 8 shows the light sensitivity of one of the
image sensors. As can be seen, the sensitivity of the image sensor
to red, green and blue light is localized around the appropriate
frequencies. However at light in the infrared range i.e. about 850
nm, the color filters of the image sensors become transparent
making the sensitivity of all of the pixels of the image sensors
basically equal. This characteristic of the image sensor allows the
touch screen to be operated in a number of modes depending on
ambient light levels as will now be described.
[0072] For example, in one mode of operation when the ambient light
level is sufficiently high, the illuminated bezels 262 are switched
off allowing color images to be acquired by the digital cameras
270. During image processing, in addition to determining the
pointer position in the manner described previously, acquired color
information is used to enhance pointer recognition and scene
understanding.
[0073] As will be appreciated, when an image including a pointer is
captured, the foreground object i.e. the pointer, is the object of
interest. During image processing, it is desired to separate the
foreground object from the background. Since the optical properties
of the foreground object and background are different for different
wavelengths of light, the foreground object is detected easier in
some light frequencies than others. For example, if the background
is predominately blue, then the foreground object such as a finger
will have higher luminosity when looking through red or green
filters since the blue filter does not permit blue light to pass.
This effectively segments the foreground object from the
background. In general, the luminosity differences between the
foreground object and the background are exploited at different
frequencies.
[0074] When the ambient light level drops below a threshold level,
the illuminated bezels 262 are switched on. In this case, the touch
screen 252 operates in an occlusion mode as described previously.
Pointer data is developed from images captured by the image sensors
and processed in the manner discussed above.
[0075] Although the touch screen 252 has been described as using
infrared illumination to provide backlighting, those of skill in
the art will appreciate that light in a different frequency range
other than infrared may be used provided the image sensors in the
digital cameras have sufficient quantum efficiency at that
different frequency range to capture images.
[0076] Rather than exclusively using ambient light when the ambient
light level is sufficiently high and infrared illumination when the
ambient light level is low, infrared illumination can be
multiplexed with ambient light to enable the digital cameras 270 to
capture different types of images. For example, the illuminated
bezels 262 can be strobed so that one or more images are captured
by the digital cameras 270 in ambient light conditions and then in
infrared backlighting conditions. The strobing may be achieved by
shutting the illuminated bezels 262 on and off and relying on
ambient light levels in the off condition.
[0077] Alternatively, rather than using colour image sensors,
monochrome sensors may be used in conjunction with an illumination
source that provides lighting across the touch surface that changes
frequency bands allowing one or more images to be captured by the
digital cameras in the different frequency bands. For example, the
illumination source may include a white light source and a light
filter in the form of a wheel that is rotatable in front of the
light source. The wheel may include alternating infrared and clear
sections. When a clear section is presented in front of the light
source, white light is projected across the touch surface and when
an infrared section is presented in front of the light source,
infrared light is projected across the touch surface.
[0078] Other light filters can of course be used with the wheel.
For example, the wheel may include infrared, blue, red and green
sections arranged about the wheel. Depending on the section of the
wheel positioned in front of the light source, light in a different
frequency band is projected across the touch surface allowing one
or more images to be captured during each type of illumination. Of
course, those of skill in the art will appreciate that colour
wheels may be disposed in front of the digital cameras rather than
adjacent the light source.
[0079] Although embodiments of the present invention have been
described, those of skill in the art will appreciate that
variations and modifications may be made without departing from the
spirit and scope thereof as defined by the appended claims.
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