An EXPANSION CARD that enables a personal computer to create a graphical display. The term harks back to the original 1981 IBMPC which could display only text, and required such an optional extra card to ‘adapt’ it to display graphics.

The succession of graphics adapter standards that IBM produced throughout the 1980s (CGA,EGA,VGA)both defined and confined the graphics capability of personal computers until the arrival of IBM-compatibles and the graphical Windows operating system, which spawned a whole industry manufacturing graphics adapters with higher capabilities.

Nowadays most graphics adapters are also powerful GRAPHICS ACCELERATOR capable of displaying 24-bit colour at resolutions of 1280 x 1024 pixels or better. Providing software support for the plethora of different makes of adapter has become an onerous task for software manufacturers.

Pictures on a computer display or the process of creating pictures on a computer display. The term came into use when there was still a distinction between computers that could display only text and those that could also display pictures. This distinction is lost now that almost all computers employ a GRAPHICAL USER INTERFACE.

Since a computer can ultimately deal only with binary numbers, pictures have to be DIGITIZED (reduced to lists of numbers) in order to be stored, processed or displayed. The most common graphical display devices are the CATHODE RAY TUBE inside a monitor, and the PRINTER, both of which present pictures as two-dimensional arrays of dots. The most natural representation for a picture inside the computer is therefore just a list of the colours for each dot in the output; this is called a BITMAPPED representation. Bitmapping implies that each dot in the picture corresponds to one or more bits in the computer’s video memory.

An alternative representation is to treat a picture as if it were composed of simple geometric shapes and record the relative positions of these shapes; this is called a vector representation (see more under VECTOR GRAPHICS). A typical vector representation might build up a picture from straight lines, storing only the coordinates of the endpoints of each line.

Vector and bitmapped representations have complementary strengths and weaknesses. Most modern output devices work by drawing dots, which makes it more efficient to display bitmapped images. There are a few, mostly obsolete, display technologies, such as the GRAPH PLOTTER or the VECTOR DISPLAY tube, that can draw lines directly, but it is more typical for a vector image to be first converted into bitmap (the process called RENDERING) before displaying it on a dot-oriented device. Rendering involves extra work for the computer, which is performed either by software or by special hardware called a GRAPHICS ACCELERATOR.

Vector representations are easily edited by moving, resizing or deleting individual shapes, whereas in a bitmap all that can be changed is the colour of the individual pixels. Vector images can easily be rotated and scaled to different sizes with no loss of quality, the computer simply multiplying the endpoint coordinates by a suitable factor. A bitmap, on, the other hand, can be magnified only by duplicating each pixel, which gives an unsightly jagged effect.

Vector representations are most suitable for pictures that are actually drawn on the computer (such as engineering drawings, document layouts or line illustrations), and for images that must be reproduced at various sizes (such as fonts). On the other hand, bitmaps are more suitable for manipulating photographs of real world scenes and objects that contain many continuously varying colours and ill-defined shapes – both scanners and digital cameras produce bit-mapped images as their output.

A class of techniques for shrinking the size of a data file to reduce its storage requirement, by processing the data it contains using some suitably reversible algorithm. Compression methods tend to be more effective for a particular kind of data, so that text files will typically be compressed using a different algorithm from graphics or sound files.

For example RUN-LENGTH EN-CODING is very effective for compressing flat-shaded computer graphics, which contain many long runs of identical PIXEL values, but is quite poor for compressing tonally rich photographic material where adjacent pixels are different. Dictionary-based algorithms such as LEMPELZIV COMPRESSION are very effective for compressing text, but perform poorly on binary data such as pictures or sound.

Compression may be applied automatically by an operating system or application, or applied manually using a utility program such as PKZIP, TAR, LHA or STUFFITS.

Also known as vector graphics, object-oriented graphics are shapes represented with mathematical formulas. (This is very different from bitmapped graphics, in which the image is mapped to the pixels on the screen, dot by dot.)

 In a program that uses object-oriented graphics, each separate element you draw-every circle, every line, and every rectangle-is defined and stored as a separate object. Each object is defined by its vector points, or end points. Because each graphic object is defined mathematically, rather than as a specific set of dots, you can change its proportions, or make it larger or smaller, or resize it, stretch it, rotate it, change its pattern, etc

 without distorting the line width or affecting the object’s sharpness and clarity (the resolution). Because each object is a separate entity, you can overlap objects in any order and change that order whenever you feel like it. To select a graphical object in an object-oriented graphics program, you usually just click on the object with the pointer. When you select it, a set of handles, little black squares, appear on or around the object (compare marquee). By dragging the handles, you can change the size or shape of the object or the curviness of any curved lines. You can also copy or cut a selected object to the Clipboard, or move it around on the screen, without disturbing any other object

 The resolution of object-oriented graphics is device independent. This means that if you print a graphic image to a printer that has a resolution of 300 dots per inch, the graphic will print at 300 dots per inch. If you print the same image to an image setter that has a resolution of 2540 dots per inch, the graphic will print at 2540 dots per inch. (Bitmapped graphics, though, always print at the same resolution.)

Fonts, or typefaces, can also be objected-oriented, but they’re not usually referred to this way-instead, such fonts are also known as outline fonts, scalable fonts, or vector fonts.

A graphical user interfaceis fondly called “GUI” pronounced “gooey.” The word “graphical” means pictures; “user” means the person who uses it; “interface” means what you see on the screen and how you work with it. So a graphical user interface, then, means that you (the user) get to work with little pictures on the screen to boss the computer around, rather than type in lines of codes and commands.

(GUI) An INTERACTIVE outer layer presented by a computer software product (for example an operating system) to make it easier to use by operating through pictures as well as words. Graphical user interfaces employ visual metaphors, in which objects drawn on the computer’s screen mimic in some way the behaviour of real objects, and manipulating the screen object controls part of the program.

A graphical user interface usesmenusandicons(pictorial representations) to choose commands, start applications, make changes to documents, store files, delete files, etc. You can use the mouse to control a cursor or pointer on the screen to do these things, or you can alternatively use the keyboard to do most actions. A graphical user interface is considereduser-friendly.

The most popular GUI metaphor requires the user to point at pictures on the screen with an arrow pointer steered by a MOUSE or similar input device. Clicking the MOUSE BUTTONS while pointing to a screen object selects or activates that object, and may enable it to be moved across the screen by dragging as if it were a real object

Take, for example, the action of scrolling a block of text that is too long to fit onto the screen. A non-graphical user interface might offer a ‘scroll’ command, invoked by pressing a certain combination of keys, say CTRL+S. Under a GUI, by contrast, a picture of an object called a SCROLLBAR appears on the screen, with a movable button that causes the text to scroll up and down according to its position. Similarly, moving a block of text in a WORD PROCESSOR that employs a GUI involves merely selecting it by dragging the mouse pointer across it until the text becomes HIGHLIGHTED, then dragging the highlighted area to its intended destination.

There is now an accepted ‘vocabulary’ of such screen objects which behave in more or less similar ways across different applications, and even across different operating systems. These include: WINDOWS, ICONS, pull down and pop-up MENUS, BUTTONS and button bars, check boxes, dialogues and tabbed property sheets. Variants of these GUI objects are used to control programs under Microsoft Windows, Apple’s MacOS, and on UNIX systems that have a windowing system such as Motif or KDE installed.

GUIs have many advantages and some disadvantages. They make programs much easier to learn and use, by exploiting natural hand-to-eye coordination instead of numerous obscure command sequences. They reduce the need for fluent typing skills, and make the operation of software more comprehensible and hence less mysterious and anxiety- prone. For visually-oriented tasks such as word processing, illustration and graphic design they have proved revolutionary.

On the deficit side, GUIs require far more computing resources than older systems. It is usual for the operating system itself to draw most of the screen objects (via SYSTEM CALLS) to relieve application programs from the overhead of creating them from scratch each time, which means that GUI-based operating systems require typically 100 to 1000 times more working memory and processing power than those with old text-based interfaces.

GUIs can also present great difficulties for people with visual disabilities, and their interactive nature makes it difficult to automate repetitive tasks by batch processing. Neither do GUIs automatically promote good user interface design. Hiding 100 poorly-chosen commands behind the tabs of a property sheet is no better than hiding them among an old-fashioned menu hierarchy – the point is to reduce them to 5 more sensible ones

Historically, the invention of the GUI must be credited to Xerox PARC where the first GUI based workstations – the XEROX STAR and XEROX DORADO – were designed in the early 1970s. These proved too expensive and too radical for commercial exploitation, but it was following a visit to PARC by Steve Jobs in the early 1980s that Apple released the LISA, the first commercial GUI computer, and later the more successful MACINTOSH. It was only following the 1990 release of Windows version 3.0 that GUIs became ubiquitous on IBM-compatible PCs.

Dithering is a trick many graphic applications use to fool your eye into seeing a whole lot more colors (or grey tones) on the screen than are really there. The computer achieves this optical illusion by mixing together different colored pixels (tiny dots on the screen that make up an image) to trick the eye into thinking that a totally new color exists. For instance, since pixels are so tiny, if the computer intermingles a series of black with white dots then you’re going to think you’re seeing gray.

Color dithering smoothes out images by creating intermediate shades between two more extreme colors (called a blend). Dithering also makes the best use of the limited number of available colors, like when you open a 24-bit color image (millions of colors) on a computer that’s only capable of displaying 8-bit (256 colors).

There is a half tone effect for black-and-white images called dithering. Rather than dots of varying sizes, a dithered image has dots or squiggles all the same size, arranged in such a way as to create the illusion of gray values