1 CP586 © Peter Lo 2003 Multimedia Communication Video Fundamentals.
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Transcript of 1 CP586 © Peter Lo 2003 Multimedia Communication Video Fundamentals.
CP586 © Peter Lo 2003 1
Multimedia CommunicationMultimedia Communication
Video Fundamentals
CP586 © Peter Lo 2003 2
Frames Per Second (FPS)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 2003 3
Broadcast TV StandardsBroadcast TV Standards NTSC: National Television Standards Committee,
525 (LPS) lines per screen, 29.97 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 2003 4
The Computer ScreenThe 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 2003 5
Video AdaptorsVideo 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 2003 6
Cathode-Ray Tube (CRT)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 2003 7
Liquid Crystal Display (LCD)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 2003 8
Refresh RateRefresh 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 2003 9
InterlacingInterlacing 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 2003 10
Video CardVideo 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 2003 11
Video Card AcceleratorVideo 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 2003 12
Video ChipsetVideo 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).