Transcript Document

MULTI TOUCH
Introduction
 Multi-touch is a human-computer interaction
technique.
 Consists of a touch screen as well as software
that recognizes multiple simultaneous touch
points.
 Multi touch using Frustrated Total Internal
Reflection
 Enables high-resolution multi touch sensing on
rear-projected interactive surfaces.
 interact with more than one finger at a time and
also able to accommodate multiple users
simultaneously
Developments
In 2007 Apple unveiled the iPhone
In 2007 Microsoft introduced MS, a
functional multitouch table-top computer
based on a standard PC platform.
Technique
The technique used in multi touch is
frustrated total internal reflection (FTIR).
It was introduced by Jefferson Y. Han who
founded a company Perceptive Pixel.
Han envisions large collaborative spaces
that will allow multiple users to work and
interact.
Perceptive Pixel’s technology is currently
being utilized, in the form of the Multi-Touch
Collaboration Wall.
Frustrated Total Internal Reflection (FTIR)
 Total internal reflection is an optical
phenomenon that occurs when a ray of light
strikes a medium boundary at an angle larger
than the critical angle with respect to the
normal to the surface.
 If the refractive index is lower on the other side
of the boundary no light can pass through, so
effectively all of the light is reflected.
 The critical angle is the angle of incidence above
which total internal reflection occurs.
FTIR
critical angle is given
by:
Where n2 is the
refractive index of the
less dense medium,
and n1 is the refractive
index of the denser
medium
FTIR
 if the angle of incidence is greater than the
critical angle, then the light will stop crossing
the boundary and be totally reflected back
internally.
 This occur when light travels from a medium
with a higher refractive index to one with a
lower refractive index.
 Side effect of total internal reflection is the
propagation of an evanescent wave across the
boundary surface.
 evanescent wave travel along the boundary
between the two materials. This wave leads to
a phenomenon known as frustrated total
internal reflection.
FTIR
Under "ordinary conditions" evanescent
wave transmits zero net energy
If a third medium with a higher refractive
index than the second medium is placed
and it will pass energy across the second
into the third medium.
Requirements
Hardware
IR led’s
Acrylic
Camera
projector
computer
Acrylic with led’s at its edges
Software
several languages /programming
environments are used
Eg;Processing (P5), Flash, C, C++, Java
Working
• infrared light is beamed inside
the acrylic and reflects
internally.
 as a finger touches the acrylic
surface, the internal reflection
of the IR-light, is interrupted.
 The images that are generated
by the camera contain white
blobs
 Every blob corresponds to
certain coordinates
 Software can by analyzing
these coordinates perform
certain tasks
Working
Multiple points are obtained on the camera
Each point is a pixel position
Each point locations are identified and all
operations are performed
(a) IR view of a touch (b) Pixel positions
located on screen
Advantages
Multi touch based on FTIR is a simple and
inexpensive technique.
enables high-resolution graphics
It acquires true touch image information at
high spatial and temporal resolutions.
It is scalable to large installations.
Larger shared-display systems
Disadvantages
being camera-based, it requires a
significant amount of space behind the
interaction surface
as an optical system, it remains
susceptible to harsh lighting environments.
Application
 Personal computers, Laptops, Tabletops, Graphics
Tablets.
 It supports both LCD and CRT monitors.
 Telephones, Watches, PDAs, Mobile phones.
 Advanced multi touch Gaming with high graphics support
 Governmental, office and business purposes
 An enhanced multimedia experience including audio, video
and photo sharing
 Enhanced dining experience
 Concierge service
 Concept mapping
 Collaboration and instruction on Interactive Whiteboards
Conclusion
There are many ways to make a multi-touch
screen. Some of the early designs measured the
change in electrical resistance or capacitance on
a surface when fingers touched it. But these
devices have limited resolution, are relatively
complex, and don't easily and inexpensively
scale up to large dimensions. Multi-touch
technologies have a long history. This technique
using FTIR is simple and easy to implement. It
provides any resolution displays supported with
high graphics .The applications being both made
and proposed are plenty in number.
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