Graphics Systems

The two main elements required by graphics systems for displaying pictures with fast response time are hardware and software. Hardware is the electronic device which is capable of computing and manipulating information whereas software is responsible for controlling, integrating, and managing the hardware components of a computer. Hardware can be further categorized into input devices (which allow the user to feed into the computer) and output devices (which convert machine-readable into human-readable form). Some standard input device hardware for graphics systems includes keyboards, light pens, mouse, digitizing tablets, etc., while output device hardware includes plotters, printers, and graphics display on the monitor. The monitors are based on cathode ray tubes (CRT), direct view storage tubes (DVST), liquid crystal display (LCD), plasma, and other more techniques. On the other hand, software of computer graphics includes integration of the man-machine interface, packages, programming languages and operating system in modular form.

Refresh rate

refers to the number of times per second the pixels are recharged so that their glow remains bright. Generally, screen pixels are made from phosphor and they need to be refreshed periodically because the phosphors hold their glow for just a fraction of a second. The refresh rate for a monitor is measured in Hertz (Hz) and varies from 60-75Hz. A refresh rate of 60Hz means that image is redrawn 60 times a second. The higher the refresh rate, the more solid the image looks on the screen, that is, it does not flicker.

CRT uses different kinds of phosphors which are different in terms of their persistence (that is, for how long it continues to glow). In technical terms, persistence is defined as the time it takes the emitted light from the screen to decay to one-tenth of its original intensity. However, different phosphors are used for different purposes depending on their persistence. A low-persistence phosphor is used for animation and it requires high refresh rates in order to maintain its steadiness; whereas a high-persistence phosphor is used for displaying static and highly complex pictures.

Resolution

refers to the number of pixels (points per centimetre) that can be plotted in the horizontal and vertical directions on the screen. It can be of two types, namely, medium resolution graphics (where pixels are large) and high-resolution graphics (where pixels are small). Nowadays, most video display units operate on the basis of standard CRT design. With reference to CRT, resolution refers to the number of points which can be displayed on it without being overlapped. The average CRT resolution is currently 800 × 600 or 1024 × 768. However, resolution of high-quality systems (also known as high-definition systems) is 1280 × 1024. Large number of dots, or screen points result in sharper image. Therefore, a resolution of 1280 × 1024 will produce sharper images (for example, smaller icons and more information) than one of 800 × 600.

Aspect ratiois the ratio of the width of the display screen to the height, that is, the ratio of vertical points to the horizontal points necessary to produce equal-length lines in both directions on the screen. Generally, computer displays have an aspect ratio of 4:3. It means that a vertical line plotted with three points has the same length as a horizontal line plotting with four points.

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