Screen and Pixels

Your PC's monitor is based on cathode ray tube (CRT). It uses the Red-Green-Blue (RGB) color model. We will see more about RGB and other color models later. The computer's operating system (MacOs, Windows and so on) 'sees' your monitor like a sort of chess-board composed by thousands of very small squares. Each small square of the chess-board is called 'pixel' (well, each pixel is not a square, but it is a very small dot). Pixel stands for picture element (short for picture element, PIX ELement). Now consider that anything you see on your monitor is an image composed by dots. There are thousands of dots in your screen. These dots are called 'pixels' exactly. You can think of a pixel as a very small light bulb. Each of these 'light bulbs' can be switched on or off. Besides each of them can be colored (to see pixels, observe your screen using a magnifying glass: you will be able to see these 'light bulbs'). To control the color of each pixel, the operating system has to use a small amount of memory for each of them. This kind of memory is called Video RAM or VRAM (Video Random Access Memory). On black and white computer displays, for each pixel there is a corresponding bit of memory switched on or off ('bit' stands for Binary digIT and it represents the smallest amount of information storable for any computer. Its value can be '0' or '1' only). When more bits of memory are dedicated to each pixel, computers can handle colors too. If you use 8 bits for each pixel, you can handle up to 256 colors (256 is the maximum number of combinations you can get using 8 bits: '00000000', '00000001', '00000010', '00000011', '00000100', '00000101' and so on, up to '11111111'). If you use 24 bits for each pixel, you can get nearly photographic color ('True-Color') on your screen. In fact you can get 16777216 of colors! Anyway, some computer screens can handle more pixels than others. The amount of pixels that a computer can handle is called 'screen resolution'. The more 'light bulbs' your screen have, the more definite images are. The resolution that you have depends on your video board and your monitor and it can be considered as the geometrical screen's area. Your screen can be represented as a rectangle so its resolution is determined multiplying its width by its height (in fact to know a rectangle's area you have to multiply its width by its height). There are several screen resolutions (640x480, 1024x760 or 1280x1024 for example) but the commonest is 800x600 pixels. The resolution of any image is specified in DPI (dots per inch). For example, 96 dpi means 96 x 96 pixels (9216 pixels) for a square inch.