# computer graphics

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## computer graphics,

the transfer of pictorial data into and out of a computercomputer,
device capable of performing a series of arithmetic or logical operations. A computer is distinguished from a calculating machine, such as an electronic calculator, by being able to store a computer program (so that it can repeat its operations and make logical
. Using analog-to-digital conversionanalog-to-digital or A/D conversion,
the process of changing continuously varying data, such as voltage, current, or shaft rotation, into discrete digital quantities that represent the magnitude of the data compared to
techniques, a variety of devices—such as curve tracers, digitizers, and light pens—connected to graphic computer terminalscomputer terminal,
a device that enables a computer to receive or deliver data. Computer terminals vary greatly depending on the format of the data they handle. For example, a simple early terminal comprised a typewriter keyboard for input and a typewriter printing element for
, computer-aided designcomputer-aided design
(CAD) or computer-aided design and drafting
(CADD), form of automation that helps designers prepare drawings, specifications, parts lists, and other design-related elements using special graphics- and calculations-intensive computer programs.
programs, or optical scanners can be used to store pictorial data in a digital computer. By reversing the process through digital-to-analog conversiondigital-to-analog or D/A conversion,
the process of changing discrete digital data into a continuously varying signal in relation to a standard or reference.
techniques, the stored data can be displayed in graphical form on a mechanical plotting board, or plotter, or on a televisionlike graphic display terminal. Raster graphics stores and displays images as a bit map, a series of closely spaced dots (or pixels) arranged in rows and columns. Vector, or object-oriented, graphics stores the images as mathematical formulas; images are displayed by calculating the coordinates of the end points and then drawing lines between them. Computer graphics capabilities range from the simple display of digital tabulations as line graphs and pie charts to complex animation and elaborate special effects for television and motion pictures. Computer graphics are used in architecture, art, computer-aided design, electronic gameselectronic game,
device or computer program that provides entertainment by challenging a person's eye-hand coordination or mental abilities. Made possible by the development of the microprocessor, electronic games are marketed in various formats, such as hand-held one-player
, flight simulatorsflight simulator,
device providing a controlled environment in which a flight trainee can experience conditions approximating those of actual flight. A simulator generally consists of an enclosure housing a working replica of the interior of the cockpit of an aircraft.
for pilot training, and molecular modelingmolecular modeling,
the computer simulation, by various means, of chemical structures or processes. Special computer-graphics programs can display three-dimensional images of molecular structures and chemical processes, showing the distances and angles of chemical bonds and the
.

### Bibliography

See J. D. Foley, Computer Graphics: Principles and Practices (1990); K. S. Chauveau, J. S. Chin and T. N. Reed, The Computer Graphics Interface (1991); Sun Microsystems, An Introduction to Computer Graphics Concepts: From Pixels to Pictures (1991); R. T. Stevens, Quick Reference to Computer Graphics Terms (1993); I. V. Kerlow and J. Rosebush, Computer Graphics for Designers and Artists (2d ed. 1994); J. Peddie, High-Resolution Graphics Display Systems (1994).

## computer graphics

[kəm′pyüd·ər ′graf·iks]
(computer science)
The process of pictorial communication between humans and computers, in which the computer input and output have the form of charts, drawings, or appropriate pictorial representation; such devices as cathode-ray tubes, mechanical plotting boards, curve tracers, coordinate digitizers, and light pens are employed.

## Computer graphics

A branch of computer science that deals with the theory and techniques of computer image synthesis. Computers produce images by analyzing a collection of dots, or pixels (picture elements). Computer graphics is used to enhance the transfer and understanding of information in science, engineering, medicine, education, and business by facilitating the generation, production, and display of synthetic images of natural objects with realism almost indistinguishable from photographs. Computer graphics facilitates the production of images that range in complexity from simple line drawings to three-dimensional reconstructions of data obtained from computerized axial tomography (CAT) scans in medical applications. User interaction can be increased through animation, which conveys large amounts of information by seemingly bringing to life multiple related images. Animation is widely used in entertainment, education, industry, flight simulators, scientific research, and heads-up displays (devices which allow users to interact with a virtual world). Virtual-reality applications permit users to interact with a three-dimensional world, for example, by “grabbing” objects and manipulating objects in the world. Digital image processing is a companion field to computer graphics. However, image processing, unlike computer graphics, generally begins with some image in image space, and performs operations on the components (pixels) to produce new images.

Computers are equipped with special hardware to display images. Several types of image presentation or output devices convert digitally represented images into visually perceptible pictures. They include pen-and-ink plotters, dot-matrix plotters, electrostatic or laser-printer plotters, storage tubes, liquid-crystal displays (LCDs), active matrix panels, plasma panels, and cathode-ray-tube (CRT) displays. Images can be displayed by a computer on a cathode-ray tube in two different ways: raster scan and random (vector) scan. See Cathode-ray tube, Computer peripheral devices

Interaction with the object takes place via devices attached to the computer, starting with the keyboard and the mouse. Each type of device can be programmed to deliver various types of functionality. The quality and ease of use of the user interface often determines whether users enjoy a system and whether the system is successful. Interactive graphics aids the user in the creation and modification of graphical objects and the response to these objects in real-time. The most commonly used input device is the mouse. Other kinds of interaction devices include the joystick, trackball, light pen, and data tablet. Some of these two-dimensional (2D) devices can be modified to extend to three dimensions (3D). The data glove is a device capable of recording hand movements. The data glove is capable of a simple gesture recognition and general tracking of hand orientation.

In the production of a computer-generated image, the designer has to specify the objects in the image and their shapes, positions, orientations, and surface colors or textures. Further, the viewer's position and direction of view (camera orientation) must be specified. The software should calculate the parts of all objects that can be seen by the viewer (camera). Only the visible portions of the objects should be displayed (captured on the film). (This requirement is referred to as the hidden-surface problem.) The rendering software is then applied to compute the amount and color of light reaching the viewer eye (film) at any point in the image, and then to display that point. Some modern graphics work stations have special hardware to implement projections, hidden-surface elimination, and direct illumination. Everything else in image generation is done in software.

Solid modeling is a technique used to represent three-dimensional shapes in a computer. The importance of solid modeling in computer-aided design and manufacturing (CAD/CAM) systems has been increasing. Engineering applications ranging from drafting to the numerical control of machine tools increasingly rely on solid modeling techniques. Solid modeling uses three-dimensional solid primitives (the cube, sphere, cone, cylinder, and ellipsoid) to represent three-dimensional objects. Complex objects can be constructed by combining the primitives. See Computer-aided design and manufacturing, Computer-aided engineering

The creation of images by simulating a model of light propagation is often called image synthesis. The goal of image synthesis is often stated as photorealism, that is, the criterion that the image look as good as a photograph. Rendering is a term used for methods or techniques that are used to display realistic-looking three-dimensional images on a two-dimensional medium such as the cathode-ray-tube screen (see illustration). The display of a wire-frame image is one way of rendering the object. The most common method of rendering is shading. Generally, rendering includes addition of texture, shadows, and the color of light that reaches the observer's eye from any point in the image.

Image renderings of a teapot

Computer-generated images are used extensively in the entertainment world and other areas. Realistic images have become essential tools in research and education. Conveying realism in these images may depend on the convincing generation of natural phenomena. A fundamental difficulty is the complexity of the real world. Existing models are based on physical or biological concepts. The behavior of objects can be determined by physical properties or chemical and microphysical properties.

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