If you have used an interactive video wall or a tabletop PC, chances are, you have also used a touch screen that was built using optical touch technology.
Optical touch technology uses CMOS infrared cameras placed on top of the panel to continuously monitor the field of view. Optical touch screens also use infrared light, similar to infrared touch screen technologies, but the layout of the emitters and sensors is what differentiates it.
Most optical touch screens use two cameras placed in the corners at the top of the screen. These cameras are used to look across the entire touch surface for touch events. When an object touches the screen, it blocks some of the light being received by the sensors in the cameras. The location of the touch is then calculated by using the information from both cameras and the mathematical principles of triangulation.
Optical touch screens fall into categories: passive and active. Passive screens use light that is generated by the cameras and reflected back by the side and bottom edges, while active screens use light that is emitted directly from LEDs along the side and bottom edges. Both systems rely on the cameras to detect the light and determine the location of the touch event.
Pros of Optical Touch Screens
The Baanto ShadowSense Advantage
Optical touch screens have a number of issues that can impact their performance. ShadowSense touch screens do not use cameras; instead, LEDs embedded in the bezel emit infrared light and sensors detect the shadows cast by the object touching the surface. The implementation is much more elegant when compared to optical touch screens.
|Cons of Optical Touch Screens||ShadowSense Benefits|
|Performance can be affected by direct sunlight or reflections from wet or shiny surfaces||Built-in notch and band pass filters in the screen allow the sensor to see only the light emitted by the LEDs, making it immune to ambient light|
|Needs drivers for image processing which take up significant CPU resources, impacting performance||Response times are around 6 to 8 ms, because screens do not need drivers or CPU support, as touch processing is done by the built-in controller|
|Large screens are difficult to manufacture as sensors have to be aligned accurately||Screens, even if they are very large, can be cost effectively fabricated|
|Lenses have limited field of view, and have blind spots in the corners||Field of view is 180 degrees, and touch events can be detected over the entire surface of the screen|
|Multi touch performance not accurate due to ghosting because of limited number of image sensors||Screens have 4 to 6 ShadowSensors to reduce ghosting compared to optical screens of similar size|
Read about capacitive touch screen.