Many kinds of tablet computers (tablets for short) have been recently released onto the market. There is no doubt that the primary interface of the tablet is a capacitive touchscreen that can provide users with a fluid and intuitive multi touch function. It is attributable to the fact that the capacitive touchscreen can measure a minute change of a capacitance. On the other hand, the high sensitivity of the touchscreen can cause an undesirable effect when users write or draw. Base on user feedbacks, this has been causing some inconvenience. This study is focusing on how to discriminate non-fingertip contact such as a grip, palm and fist, and to suppress them from image processing point of view.