TouchFree Switch (TFS) is an access tool for physically disabled users
which was developed jointly by the Exploratory Computer Vision Group and
Edmark.
To understand TFS, it is important to understand
scanning software,
which can be controlled by pressing a single key or switch.
In a nutshell TFS replaces the physical switches, which are generally used
to control scanning, with a camera that can be trained to respond to nearly
any movement a user can make.
TFS is based on a modality we refer to as
target-based interaction.
A portion of the image called a target is trained
to respond to a specific change. When it senses that change, the
target triggers a user interface event. For example a user could
click the mouse by tipping their head, as shown above (right).
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To use TFS, the user (or in most cases, a therapist working with a disabled
user) aims the camera at whatever part of the body they wish to use to
"click". A video window is displayed with a rectangular target superimposed
over it. The target is moved and resized so that the user's movement
changes the image within the target. Once the target is in place,
the user demonstrates the movement as they press a key so the target learns
to recognize that specific change. There are options in TFS so that
the user can set the target to be more or less sensitive to variations,
like changes in lighting, as well as adjust the event which is generated.
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Once everything
is set up, the user starts TFS running. At that point the video shrinks
to a small window in the corner of the screen, so that the user gets some
feedback about what the computer sees. Whenever they move into the
target an event is sent to the current foreground application.
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There are several advantage TFS has over physical switches. It is more
flexible, the camera can recognize nearly any motion, potentially replacing
several kinds of switches. TFS requires no physical strength to trigger
an event. It can be easily reconfigured to use another motion if
the user begins to tire. The hardware is generally more simple than
with switches as well - switches often need to plug into interface boxes
that in turn plug into the serial or keyboard port. TFS uses only
a standard USB camera.
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