A graphics tablet (sometimes called a digitizing tablet, graphics pad or even drawing tablet) is a computer input device that allows a user to hand-draw images and graphics, similar to the way you might draw images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures.
A graphics tablet (also called pen pad or digitizer) consists of a flat surface upon which the user may “draw” an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor. Some tablets however, come as a functioning secondary computer screen that you can interact with directly using the stylus.
Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.
Different Types of Tablet
Passive Tablets
Passive tablets, most notably those by Wacom, make use of electromagnetic induction technology, where the horizontal and vertical wires of the tablet operate as both transmitting and receiving coils (as opposed to the wires of the RAND Tablet which only transmit). The tablet generates an electromagnetic signal, which is received by the LC circuit in the stylus. The wires in the tablet then change to a receiving mode and read the signal generated by the stylus. Modern arrangements also provide pressure sensitivity and one or more switches (similar to the buttons on a mouse), with the electronics for this information present in the stylus itself, not the tablet. On older tablets, changing the pressure on the stylus nib or pressing a switch changed the properties of the LC circuit, affecting the signal generated by the pen, which modern ones often encode into the signal as a digital data stream. By using electromagnetic signals, the tablet is able to sense the stylus position without the stylus having to even touch the surface, and powering the pen with this signal means that devices used with the tablet never need batteries. Wacom’s patents don’t permit their competitors to employ such techniques.
Active Tablets
Active tablets differ in that the stylus used contains self-powered electronics that generate and transmit a signal to the tablet. These styli rely on an internal battery rather than the tablet for their power, resulting in a bulkier stylus. Eliminating the need to power the pen means that such tablets may listen for pen signals constantly, as they do not have to alternate between transmit and receive modes, which can result in less jitter.
Optical Tablets
Optical tablets operate by a very small digital camera in the stylus, and then doing pattern matching on the image of the paper. The most successful example is the technology developed by Anoto.
Acoustic Tablets
Early models were described as spark tablets—a small sound generator was mounted in the stylus, and the acoustic signal picked up by two microphones placed near the writing surface. Some modern designs are able to read positions in three dimensions.
Electromagnetic Tablets
Wacom’s are one example of a graphics tablet that works by generating and detecting an electromagnetic signal: in the Wacom design, the signal is generated by the pen, and detected by a grid of wires in the tablet. Other designs such as those by Pencept generate a signal in the grid of wires in the tablet, and detect it in the pen.
Capacitive Tablets
These have also been designed to use an electrostatic or capacitive signal. Scriptel’s designs are one example of a high-performance tablet detecting an electrostatic signal. Unlike the type of capacitive design used for touchscreens, the Scriptel design is able to detect the position of the pen while it is in proximity to, or hovering above, the tablet. Many multi-touch tablets use capacitive sensing.