Video Chapter 17 - PowerPoint PPT Presentation

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Video Chapter 17

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Title: Video Chapter 17


1
VideoChapter 17
2
Objectives
  • Explain how video displays work
  • CRT and LCD monitors
  • Understand the concept of resolution
  • Explain refresh rates and how they affect
    monitors
  • Select the proper video Card
  • Graphics Processor
  • Video Memory

3
Introduction
  • The term video encompasses a complex interaction
    among numerous parts of PC, all designed to put a
    picture on the screen.
  • Video consists of two devicesthe video card
    (display adapter)
  • and the monitor
  • (Video displays)

Video card
Monitor
4
Video Card
  • The video card consists of two distinct
    components
  • One takes commands from the computer and updates
    its own onboard RAM
  • The other scans the RAM and sends data to the
    monitor
  • Therefore Video card handles all communications
    between CPU and monitor.
  • OS needs to know how to handle communication
    between CPU and display adapter, which requires
    BIOS.

5
Monitors
6
CRT Monitors
  • CRT is Cathode Ray Tube (CRT), which is type of a
    vacuum tube.
  • One end of this tube is a slender cylinder that
    consists of three electron guns.
  • The wide end of the CRT is the display screen.

7
CRT Monitors
  • The inside of the display screen has Phosphor
    coating.
  • When power is applied to one or
  • more of the electron guns,
  • a stream of electrons shoots
  • towards the display end of CRT.
  • This stream is subjected to a magnetic field
    generated by a ring of electromagnets called a
    yoke
  • that controls the electron beams point of
    impact.

8
CRT Monitors
  • The phosphor coating releases energy as visible
    light when struck by the electrons.
  • Phosphors continue to glow momentarily after
    being struck by electron beamsquality of
    phosphors is called persistence
  • Too much persistence and the image is smeary
  • Too little persistence and the image appears to
    flicker.

9
CRT Refresh Rates
10
CRT Refresh Rates
Video data is displayed on the monitor starting
at the upper-left corner of the monitor ending to
the lower- right corner. Each line are called
raster line. How many line in screen?
  • Horizontal refresh rate (HRR)
  • The speed at which the electron beam moves across
    the screen and to be ready for the next line.
  • Vertical refresh rate (VRR)
  • The amount of time taken by the monitor to draw
    the entire screen and get the electron beam back
    to the start.

11
CRT Refresh Rates
  • The Monitor does not determine the HRR or VRR.
  • Video cards push the monitor at a given VRR, and
    then the monitor determines the HRR
  • If the VRR is set too low, youll see flicker
  • If it is set too high, youll
  • have a distorted screen image
  • and may damage the monitor.
  • Multisync (multiple-frequency monitor) monitors
    support multiple VRRs.

12
Phosphors
  • Phosphors are dots inside the CRT monitor that
    glow red, green, or blue when an electron gun
    sweeps over them.
  • CRT has three electron guns one for read
    Phosphor, one for green Phosphors and one for
    blue Phosphors.
  • The higher the intensity of the electron stream
    the higher the color produced by Phosphors.

13
Phosphors
  • How we can prevent the red electron beam from
    bleeding over and lighting neighboring blue and
    green dots?
  • Shadow mask is a screen that enables only the
    proper electron gun to light the proper phosphor.
  • The area of phosphors lit at one time by a group
    of guns is called a picture element, or pixel

14
Phosphors
Triad
  • A pixel consists of at least 3 phosphor dots

15
Resolution
  • Resolution is always shown as the number of
    Horizontal Pixel times the Vertical Pixel.
  • A resolution of 640 X 480 means
  • Number of horizontal pixel is 640 and vertical
    pixel is 480.
  • If you multiply the values together you get
    307200? What does it means?
  • Resolution affecting the pixel
  • size.

16
Common Resolutions
  • 640x480 307,200 pixels per screen
  • 800x600
  • 1024x768
  • 1280x960
  • 1280x1024
  • 1600x1200
  • Most of these resolutions matches a 43 ratio
    (called aspect ratio)
  • Many monitors (wide-screen monitors) have 169 or
    1610 ratio. Ex. 1366x768 and 1920x1200

17
Resolution
  • Maximum possible resolution
  • Determined by how small can one pixel be.
  • Theoretically, a triad, but various limitations
    in screens, controlling electronics, and electron
    gun technology make smallest pixel much bigger
    than one triad.

18
Dot Pitch
  • Dot pitchdiagonal distance between phosphorous
    dots of the same color.
  • Range from 0.39 mm to as low as 0.18 mm
  • The lower the dot pitch, the more dots across
    the screen, which produces a sharper, more
    defined image

19
LCD monitors
  • Use Liquid crystal displays
  • Have many advantage over CRT
  • Thinner and lighter.
  • Much less power.
  • Flicker free.
  • No harmful radiation.
  • Called flat panels or flat panel displays .

20
Video Cards
21
Video Cards
  • Video cards are composed of two major pieces
  • Video RAM to store video image.
  • Video processor- GPU which takes information from
    video RAM and shoots it out to the monitor.
  • Video card need fan to cool their onboard
    processor.
  • Monitor plugs into the
  • video card.

22
Color depth
  • Each pixel in screen has color
  • This color are stored in video RAM using tiny
    number of bits depend on the number of color you
    want.
  • i.e. to get 256 colors, each pixel would have to
    be represented with 8 bits.
  • Color depths determined by bits per pixel
  • 2 colors 1 bit (mono)
  • 4 colors 2 bits
  • 16 colors 4 bits
  • 256 colors 8 bits

23
Color depth
  • Windows XP offers 32-bit color.

24
Video RAM Requirements
  • Depends on Resolution Colour Depth

1024 x 768 786432 pixels per screen
Example
32 bit colour 4 bytes per pixel.
4 x 786432 3145728 bytes.
3 megabytes per screen.
25
Video Modes
  • Your video card and monitor are capable of
    showing Windows in a fixed number of different
    resolutions and color depths.
  • The choices depend on the resolutions and color
    depths the video card can push to the monitor and
    the amount of bandwidth your monitor can support.
  • Any single combination of resolution and color
    depth you set for your system is called a mode.

26
Video Modes
  • VGA

Video Graphics Array
  • Supported 640 x 480 pixels and 16 Color.
  • Every video card made in the last 15 years can
    Output as VGA, but VGA-only cards are now
    obsolete. Check Your PC?
  • Minimum display requirement by many software
    package.

27
Video Modes
  • Beyond VGA
  • SVGA, XGA, and more

Typical Device Aspect ratio Resolution Mode
PDA and small video player 43 320x240 QVGA
Small monitors 43 800x600 SVGA
Monitor and portable projector 43 1024x768 XGA
Small widescreen laptop 1610 1280x800 WXGA
LCD monitors 54 1280x1024 SXGA
Widescreen laptop 1610 1440x900 WSXGA
28
Motherboard connection
  • Data moving from video card to display has to go
    through the video cards memory chips and
    expansion bus and this can happen only so
    quickly.
  • PCI, AGP, PCIe
  • The standard PCI slot transfers 32 bits at speed
    33 Mhz, yielding a max. bandwidth of 132 MBps.
    This may be enough until you use higher
    resolution, higher color depth and higher refresh
    rate.

29
Motherboard connection
  • A typical display at 800x600 with 70 HZ refresh
    rate and 8 bit color depth. How much data per
    second has to be sent to the display?
  • 800 x 600 x 1 byte x 70 33.6 MBps.
  • Using 24-bit color, the amount of data sent jumps
    to 100.8 MBps.
  • Although 132 MBps of PCI looks sufficient, but
    most systems have more than one PCI device each
    requiring part of this throughput.

30
AGP
  • Intel answered the desire for video bandwidth
    even higher than PCI with Accelerated Graphics
    Port (AGP)
  • AGP a single special port similar to PCI slot
    dedicated to video.
  • It is derived from the 66-MHz, 32- bit PCI 2.1
    spec.
  • It uses a function called strobing that increases
    the signals 2, 4, and 8 times for each clock
    cycle (called AGP x1, x2, x4, x8)

31
AGP cont.
  • AGP has several technological advantages over
    PCI
  • It resides alone on its own personal data bus
    connected directly to Northbridge.
  • It takes advantages of pipelining commands
    similar to CPU pipelining.
  • It has a feature called sidebanding a second
    data bus that enables video card to send more
    commands to northbridge while receiving others at
    same time.

32
Accelerated Graphics Port
33
PCIe
  • PCIe developed to replace PCI and AGP.
  • PCI and AGP are using a parallel interface.
  • It is a natural evolution for video as it is
    incredibly fast, using serial communication
    method.
  • All PCIe video cards use PCIe x16 connector

34
Graphics Processor
  • Graphics Processor Unit (GPU)
  • The most important decision in buying a video
    card is the graphics processor and amount of RAM
    onboard.
  • The graphics processor handles the heavy lifting
    of taking commands from the CPU and translating
    them into coordinates and color information that
    the monitor understands and displays.

35
Graphics Processor
  • Most video processors are made by
  • NVIDIA
  • ATI
  • ATI Radeon X1950 XTX 512 MB
  • ATI Manufacturer
  • Radeon X1950 XTX Processor Model No.
  • 512 MB Amount of RAM

36
Graphics Processor
  • NVIDIA and ATI release multiple models of
    graphics processors each year
  • Most features only seen in 3-D games
  • Textures
  • Transparency
  • Shadows
  • Reflection

37
Video Memory
  • Video RAM constantly updates to reflect every
    change that takes place on the screen
  • Different video modes require different amount of
    memory.
  • DRAM slower but cheaper
  • VRAM is specialized Video RAM
  • more expensive but faster. It can read and write
    data at same time

38
Video Memory
  • WRAM (Window RAM) is slightly faster than VRAM
    but not as widely accepted
  • SGRAM (synchronous graphics RAM) is sync-ed to
    the system clock
  • Now DDR SDRAM is used.
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