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A graphics tablet or digitizer is a computer input device that enables a user to hand-draw images and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, either by tracing or entering the corners of linear poly-lines or shapes is called digitizing.
The device consists of a flat surface upon which the user may "draw" or trace 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 are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.
The first graphics tablet resembling contemporary tablets and used for handwriting recognition by a computer was the Stylator in 1957. Better known (and often mis-stated as the first digitizer tablet) is the RAND Tablet also known as the Grafacon (for Graphic Converter), introduced in 1964. The RAND Tablet employed a grid of wires under the surface of the pad that encoded horizontal and vertical coordinates in a small magnetic signal. The stylus would receive the magnetic signal, which could then be decoded back as coordinate information.
The acoustic tablet, or spark tablet, used a stylus that generated clicks with a spark plug. The clicks were then triangulated by a series of microphones to locate the pen in space. The system was fairly complex and expensive, and the sensors were susceptible to interference by external noise.
Digitizers were popularized in the mid 1970s and early 1980s by the commercial success of the ID (Intelligent Digitizer) and BitPad manufactured by the Summagraphics Corp. These digitizers were used as the input device for many high-end CAD (Computer Aided Design) systems as well as bundled with PC's and PC based CAD software like AutoCAD.
Summagraphics also made an OEM version of its BitPad which was sold by Apple Computer as the Apple Graphics Tablet accessory to their Apple II. These tablets used a magnetostriction technology which used wires made of a special alloy stretched over a solid substrate to accurately locate the tip of a stylus or the center of a digitizer cursor on the surface of the tablet. This technology also allowed Proximity or "Z" axis measurement.
The first home computer graphics tablet was the KoalaPad. Though originally designed for the Apple II, the Koala eventually broadened its applicability to practically all home computers with graphics support, examples of which include the TRS-80 Color Computer, Commodore 64, and Atari 8-bit family. Competing tablets were eventually produced; the tablets produced by Atari were generally considered to be of high quality.
There have been many attempts to categorize the technologies that have been used for graphics tablets:
- 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. Activslate 50, the model used with Promethean Ltd white boards, also uses a hybrid of this technology.
- 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 tablets 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.
For all these technologies, the tablet can use the received signal to also determine the distance of the stylus from the surface of the tablet, the tilt (angle from vertical) of the stylus, and other information in addition to the horizontal and vertical positions.
Compared to touch-sensitive touchscreens, a graphics tablet generally offers much higher precision, the ability to track an object which is not touching the tablet, and can gather much more information about the stylus, but is typically more expensive, and can only be used with the special stylus or other accessories.
Some tablets, especially inexpensive ones aimed at young children, come with a corded stylus, using technology similar to older RAND tablets, although this design is no longer used on any normal tablets.
After styli, pucks are the most commonly used tablet accessory. A puck is a mouse-like device that can detect its absolute position and rotation. This is opposed to mice, which can only sense their relative velocity on a surface (most tablet drivers are capable of allowing a puck to emulate a mouse in operation, and many pucks are marketed as "mice".) Pucks range in size and shape, some are externally indistinguishable from a mouse, while others are fairly large device with dozens of buttons and controls. Professional pucks often have a reticle or loupe which allows the user to see the exact point on the tablet's surface targeted by the puck, for detailed tracing and computer aided design (CAD) work.
Embedded LCD tablets 
Graphics tablet/screen hybrids offer advantages over both touch screens and ordinary tablets. Unlike touch screens, they offer pressure sensitivity, and their resolution is generally higher. While their pressure sensitivity and resolution are typically no better than those of ordinary tablets, they offer the additional advantage of directly seeing the location of the physical pen device relatively to the image on the screen. This often allows for increased accuracy and a more tactile, "real" feeling to the use of the device.
Wacom holds many patents on the key technologies for graphic tablets, which forces competitors to use other technologies or license Wacom's. The displays are often sold for thousands of dollars. For instance, the Wacom Cintiq series ranges from just below US$1,000 to over US$2,000.
Some commercially available graphics tablet-screen hybrids include:
- Bosto Kingtee
- Cintiq from Wacom
- Hitachi Starboard
- Yiynova's DP10 and MSP19 products
- USync's PenStar products
- SenTIP from Hanvon
- The GD Itronix "Duo Touch" tablet PC products
- The p-active XPC-1710a and XPC-1910a
Graphics tablets, because of their stylus-based interface and ability to detect some or all of pressure, tilt, and other attributes of the stylus and its interaction with the tablet, are widely considered[according to whom?] to offer a very natural way to create computer graphics, especially two-dimensional computer graphics. Indeed, many graphics packages can make use of the pressure (and, sometimes, stylus tilt or rotation) information generated by a tablet, by modifying the brush size, shape, opacity, color, or other attributes based on data received from the graphics tablet.
In East Asia, graphics tablets, known as "pen tablets", are widely used in conjunction with input-method editor software (IMEs) to write Chinese, Japanese, Korean characters (CJK). The technology is popular and inexpensive and offers a method for interacting with the computer in a more natural way than typing on the keyboard, with the pen tablet supplanting the role of the computer mouse. Uptake of handwriting recognition among users who use alphabetic scripts has been slower.
Graphics tablets are also very commonly found in the artistic world. Using a pen on a graphics tablet combined with a graphics-editing program, such as Adobe Photoshop, gives artists a lot of precision while creating digital drawings. Photographers can also find working with a graphics tablet during their post processing can really speed up tasks like creating a detailed layer mask or dodging and burning.
Educators make use of tablets in classrooms to project handwritten notes or lessons and to allow students to do the same, as well as providing feedback on student work submitted electronically. Online teachers may also use a tablet for marking student work, or for live tutorials or lessons, especially where complex visual information or mathematical equations are required.
Finally, tablets are gaining popularity as a replacement for the computer mouse as a pointing device.[when?] They can feel more intuitive to some users than a mouse, as the position of a pen on a tablet typically corresponds to the location of the pointer on the GUI shown on the computer screen. Those artists using a pen for graphics work will as a matter of convenience use a tablet and pen for standard computer operations rather than put down the pen and find a mouse.
Graphics tablets are available in various sizes and price ranges; A6-sized tablets being relatively inexpensive and A3-sized tablets far more expensive. Modern tablets usually connect to the computer via a USB interface.
Similar devices 
Interactive whiteboards offer high resolution wall size graphic tablets up to 95" along with options for pressure and multiple input. These are becoming commonplace in schools and meeting rooms around the world.
Touch screens like those found on some tablet computers, iPads, and the Nintendo DS are operated in similar ways, but they usually use either optical grids or a pressure sensitive film instead, and therefore they do not need a special pointing device.
The graphics tablet are also used for Audio Haptic products where blind or visually impaired people touch swelled graphics on a graphic tablet and get audio feedback from that. The product that is using this technology is called Tactile Talking Tablet or T3.
See also 
- Gray, Elisha (1888-07-31), Telautograph, United States Patent 386,815
- Dimond, Tom (1957-12-01), Devices for reading handwritten characters, Proceedings of Eastern Joint Computer Conference, pp. 232–237, retrieved 2008-08-23
- Engelbart, Douglas C. (March 1967), Display-Selection Techniques for Text Manipulation, IEEE Transactions on Human Factors in Electronics, pp. 5–15, retrieved 2013-03-26
- Whetstone, A. (1971-12-07), Spark Pen, Science Accessories Corporation: United States Patent 3,626,483, retrieved 2009-11-16
- Mackintosh, Hamish (18 March 2004). "Talk time: Todd Rundgren". The Guardian.
- Pencept Penpad (TM) Manual, Pencept, Inc., 1983-06-15
- GP-10 SAC Two-dimensional Sonic Digitizer, Science Accessories Corporation, 1988-06-15
- ActivSlate 50 Product Specifications, Promethean Ltd., 2009-12, retrieved 2010-05-12
- AirPen Storage Notebook: PC NoteTaker, www.pegatech.com, 2005-06-15
- Hyperspace 3-D Digitizer, Mira Imaging, Incorporated, 1989-04-15
- New Products: CAD Graphics Tablet, IEEE Communications, Vol 22 No 4, 1984-04-15
- Kable, Robert G. (1986-07-15), Electrographic Apparatus, United States Patent 4,600,807 (full image)
- Aaron Marks (2006-11-17). "Audio Haptics for Visually Impaired Information Technology". Axistive.