A study of ambient light-independent multi-touch acquisition and interaction methods for in-cell optical touchscreens

Abstract

This thesis describes an in-cell optical touchscreen, a technology that makes use of light sensors embedded in the LCD layer. The advocates claim decreasing production costs in relation to display size, minimal affect on product design, and unlimited multi-touch functionality, as well as the possibility to acquire 3D spacial-temporal coordinates. The users would also be able to interact not only with their ngers but with all kinds of physical objects. This could challenge the well-established capacitive touch method and revolutionize the way we interact with future touchscreen devices. However, there are still many technical difficulties that needs to be solved before this could be a reality. The major obstacles are ambient light vulnerabilities and dependency on what image is displayed on the screen. This thesis investigates these matters using an in-cell optical touchscreen prototype developed at Semiconductor Energy Laboratory. The thesis compares this device with other similar hardware and their way of solving the above stated problems. Furthermore, theory for touchpoint acquisition using image processing are explained, and a new algorithm is proposed. The proposed algorithm utilizes an estimation of the ambient illumination and takes the displayed image into consideration in order to calculate touchpoints. Furthermore, other interaction methods such as nger rotation and height above the screen are investigated. Finally, an empirical evaluation was conducted to evaluate the accuracy and reliability of the proposed algorithm.