1 CP586 © Peter Lo 2003 Multimedia Communication Video Fundamentals

CP586 © Peter Lo Frames Per Second (FPS) A complete image in a sequence of moving film or video is called a frame. FPS is a measure of how much information is used to store and display motion video. Displaying frames in quick succession creates the illusion of motion.

CP586 © Peter Lo Broadcast TV Standards NTSC: National Television Standards Committee, 525 (LPS) lines per screen, fps. Used in USA, Japan and Canada. PAL: Phase Alternating Line, 625 LPS, 25 fps. Used in Australia and Europe. SECAM: Systeme Electronique Colouer avec Memoire. 625 LPS, 25 fps. Used in Eastern Europe, middle East and Africa.

CP586 © Peter Lo The Computer Screen The computer screen is non interlaced but uses faster frame rates than a TV screen. Computers use under scan. This is where you can see the entire picture. The image is usually surrounded by a black border. TV broadcasts use over scan. As a result some of the extreme edges of the picture are obscured and not shown.

CP586 © Peter Lo Video Adaptors MDA : Monochrome display adaptor. CGA : Colour graphics adaptor. EGA : Enhanced graphics adaptor. VGA : Video graphics array. SVGA : Super VGA. XGA : Extended graphics array.

CP586 © Peter Lo Cathode-Ray Tube (CRT) This technology used in most televisions and computer display screens. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen.

CP586 © Peter Lo Liquid Crystal Display (LCD) LCD displays utilise two sheets of polarising material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal like a shutter, Most LCD screens used in notebook computers are back lit to make them easier to read in bright environments. Colour LCD displays use two basic techniques for producing colour. Passive matrix : cheap, average quality. Active-matrix or thin film transistor : More expensive but equivalent to CRT displays.

CP586 © Peter Lo Refresh Rate The refresh rate for a monitor is measured in hertz (Hz) and is also called the vertical frequency, frame rate or vertical refresh rate. Using a refresh rate of 75Hz the monitor redraws the display 75 times per second. Windows 95 allows you to alter the refresh rate by altering the desktop properties.

CP586 © Peter Lo Interlacing A display technique that enables a monitor to provide more resolution inexpensively. With interlacing monitors, the electron guns draw only half the horizontal lines with each pass. Because an interlacing monitor refreshes only half the lines at one time, it can display twice as many lines per refresh cycle, giving it greater resolution..

CP586 © Peter Lo Video Card Your system's video card is the component responsible for producing the visual output from your computer. The video card is the piece of hardware that takes that output and tells the monitor which of the dots on the screen to light up (and in what colour) to allow you to see it.

CP586 © Peter Lo Video Card Accelerator A conventional video card does the job of translating what the processor produces into a form that the monitor can display. With an accelerator, when the system needs to draw a window on the screen, it doesn't compute where all the pixels need to be and what colour, it sends a request to the video card saying “draw a window at these locations” and the video card does it.

CP586 © Peter Lo Video Chipset The capabilities of the video card are a function of the internal processor that does the calculating functions. The logic circuit that controls the video card is referred to as the video chipset. There are several 3D chipsets on the market (eg Voodoo Chipset).