FREE ESSAY ON COMPUTER GRAPHICS

COMPUTER GRAPHICS

Computer graphics is the use of computers to produce pictorial images. The images produced
can be printed documents or animated motion pictures, but the term computer graphics
refers particularly to images displayed on a video display screen, or display monitor.
These screens can display graphic as well as alphanumeric data. A computer-graphics
system basically consists of a computer to store and manipulate images, a display screen,
various input and output devices, and a graphics software package for example, a program
that enables a computer to process graphic images by means of mathematical language.
These programs enable the computer to draw, color, shade, and manipulate the images held
in its memory. The programs may be broken down into four major categories: first of all
the design (computer-aided design [CAD] systems), in which the computer is used as a tool
in designing objects ranging from automobiles to bridges to computer chips by providing
an interactive drawing tool and an interface to simulation and analysis tools for the
engineer; secondly fine arts, in which artists use the computer screen as a medium to
create images of impressive beauty, cinematographic special effects, animated cartoons,
and television commercials; thirdly scientific visualization, in which simulations of
scientific events--such as the birth of a star or the development of a tornado--are
exhibited pictorially and in motion so as to provide far more insight into the phenomena
than would tables of numbers; and lastly human-computer interfaces.
A computer displays images on the phosphor-coated surface of a graphics display screen by
means of an electron beam that sweeps the screen many times each second. Those portions
of the screen energized by the beam emit light, and changes in the intensity of the beam
determine their brightness and hue. The brightness of the resulting image fades quickly,
however, and must be continuously refreshed by the beam, typically 30 times per second. 
Graphics software programs enable a user to draw, color, shade, and manipulate an image
on a display screen with commands input by a keyboard. A picture can be drawn or redrawn
onto the screen with the use of a mouse, a pressure-sensitive tablet, or a light pen.
Preexisting images on paper can be scanned into the computer through the use of scanners,
digitizers, pattern-recognition devices, or digital cameras. Frames of images on
videotape also can be entered into a computer. Various output devices have been developed
as well; special programs send digital data from the computer's memory to an imagesetter
or film recorder, which prints the image on paper or on photographic film. The computer
can also generate hard copy by means of plotters and laser or dot-matrix printers. 
Pictures are stored and processed in a computer's memory by either of two methods: raster
graphics and vector graphics. Raster-type graphics maintain an image as a matrix of
independently controlled dots, while vector graphics maintain it as a collection of
points, lines, and arcs. Raster graphics are now the dominant computer graphics
technology. 
In raster graphics, the computer's memory stores an image as a matrix, or grid, of
individual dots, or pixels (picture elements). Each pixel is encoded in the computer's
memory as one or several bits for example, binary digits represented by 0 or 1. A 2-bit
pixel can represent either black or white, while a 4-bit pixel can represent any of 16
different colors or shades of gray. The constituent bits that encode a picture in the
computer's memory are called a bit map. Computers need large processing and memory
capacities to translate the enormous amounts of information contained in a picture into
the digital code of a bit map, and graphics software programs use special algorithms
(computional processes) to perform these procedures. 
In raster graphics, the thousands of tiny pixels that make up an individual image are
projected onto a display screen as illuminated dots that from a distance appear as a
contiguous image. The picture frame consists of hundreds of tiny horizontal rows, each of
which contains hundreds of pixels. An electron beam creates the grid of pixels by tracing
each horizontal line from left to right, one pixel at a time, from the top line to the
bottom line. 
Raster graphics create uniform colored areas and distinct patterns and allow precise
manipulation because their constituent images can be altered one dot at a time. Their
main disadvantage is that the images are subtly staircased--i.e., diagonal lines and
edges appear jagged and less distinct when viewed from a very short distance. A corollary
of television technology, raster graphics emerged in the early 1970s and had largely
displaced vector systems by the '90s. 
In vector graphics, images are made up of a series of lines, each of which is stored in
the computer's memory as a vector--i.e., as two points on an x-y matrix. On a vector-type
display screen, an electron beam sweeps back and forth between the points designated by
the computer and the paths so energized emit light, thereby creating lines; solid shapes
are created by grouping lines closely enough to form a contiguous image. Vector-graphics
technology was developed in the mid-1960s and widely used until it was supplanted by
raster graphics. Its application is now largely restricted to highly linear work in
computer-aided design and architectural drafting, and even this is performed on
raster-type screens with the vectors converted into dots. 
Computer graphics have found widespread use in printing, product design and
manufacturing, scientific research, and entertainment since the 1960s. In the business
office, computers routinely create graphs and tables to illustrate text information.
Computer-aided design systems have replaced drafting boards in the design of a vast array
of products ranging from buildings to automotive bodies and aircraft hulls to electrical
and electronic devices. Computers are also often used to test various mechanical,
electrical, or thermal properties of the component under design. Scientists use computers
to simulate the behaviour of complicated natural systems in animated motion-picture
sequences. These pictorial visualizations can afford a clearer understanding of the
multiple forces or variables at work in such phenomena as nuclear and chemical reactions,
large-scale gravitational interactions, hydraulic flow, load deformation, and
physiological systems. Computer graphics are nowhere so visible as in the entertainment
industry, which uses them to create the interactive animations of video games and the
special effects in motion pictures. Computers have also come into increasing use in
commercial illustration and in the digitalization of images for use in CD-ROM products,
online services, and other electronic media