Visual Display Unit (VDU)

4:00 PM Posted In , , , , , , , , Edit This 0 Comments »
Visual Display Unit (VDU)

Visual display unit, often called simply a monitor or display, is a piece of electrical equipment which displays images generated from the video output of devices such as computers, without producing a permanent record. A newer monitor typically consists of a TFT LCD, with oldest monitors based around a cathode ray tube (CRT). The monitor comprises the display device, simple circuitry to generate and format a picture from video sent by the signals source, and usually an enclosure. Within the signal source, either as an integral section or a modular component, there is a display adapter to generate video in a format compatible with the monitor.

Imaging technologies:




19" inch
(48.3 cm tube,
45.9 cm viewable)
View Sonic CRT
computer monitor.



As with television, many different hardware technologies exist for displaying computer-generated output:

  • Liquid crystal display (LCD). TFT LCDs are the most popular display device for new computer.
    • LCDs produce poor contrast, slow response, and other image defects. These were used in most laptops until the mid 1990s.
    • Film Transistor LCDs give much better picture quality in several respects. Nearly all modern LCD monitors are TFT.


  • Cathode ray tube (CRT)
    • Raster scan computer monitors, which produce images using pixels. These were the most popular display device for older computers.
    • Displays, as used on the Vectrex, many scientific and radar applications, and several early arcade machines (notably Asteroids) - always implemented using CRT displays due to requirement for a deflection system, though can be emulated on any raster-based display.
    • Television sets were used by most early personal and home computers, connecting composite video to the television set using a modulator. Resolution and image quality were strongly limited by the display capabilities of television.



  • Plasma display
    Video projectors use CRT, LCD, DLP, LCoS or many other technologies to send light through the air to a projection screen. Front projectors use screens as reflectors to send light back, while rear projectors use screens as diffusers to refract light forward. Rear projectors are often integrated into the same case as their screen.





  • Surface-conduction electron-emitter display (SED)
  • Organic light-emitting diode (OLED) display
  • Penetron military aircraft displays

Comparison

CRT

Pros:
  1. Very high contrast ratio (20,000:1 or greater, much higher than many modern LCDs and plasma displays.)
  2. High speed response.
  3. Excellent Additive color, wide gamut and low black level limited only by external environment.
  4. Can display natively in almost any resolution and refresh rate.
  5. Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
  6. No input lag.
  7. A reliable, proven display technology.
Cons:
  1. Large size and weight (a 40" unit weighs over 200lbs)
  2. Geometric distortion in non-flat CRTs
  3. Older CRTs are prone to burn-in.
  4. Warm up time required prior to peak luminance and proper color rendering.
  5. Greater power consumption than similarly sized displays, such as LCD.
  6. Screened devices are prone to moire effect at highest resolution (does not apply to triple-tube projection)
  7. Intolerant of damp conditions, with dangerous wet failure characteristics.
  8. Small risk of implosion (due to internal vacuum) if the picture tube is broken in aging sets.
  9. Use under Lower refresh rates causes noticeable flicker
  10. Internal lethally high voltages
  11. Flyback transformer produces characteristic high-pitched noise when close to set.
  12. Increasingly difficult to obtain models at HDTV resolutions, due to consumers' perception of antiquity.

LCD

Pros:
  1. Very compact and light
  2. Low power consumption
  3. No geometric distortion
  4. Rugged
  5. Little or no flicker depending on back light.
Cons:
  1. Low contrast ratio.
  2. Limited viewing angle. This causes color, saturation, contrast and brightness to vary, even within the intended viewing angle from mere variations in posture.
  3. Uneven backlighting in some monitors can cause brightness distortion, especially toward the edges.
  4. Slow response times, which cause smearing and ghosting artifacts (although many modern LCDs have response times of 8ms or less).
  5. Only has one native resolution. Displaying other resolutions requires a video scaler, which degrades image quality at lower resolutions.
  6. Fixed bit depth, many cheaper LCDs are incapable of truecolor.
  7. Input lag
  8. Somewhat more expensive than CRT
  9. Dead pixels are possible during manufacturing

Plasma

Pros:
  1. Compact and light
  2. High contrast ratios (10,000:1 or greater)
  3. High speed response
  4. Excellent color, wide gamut and low black level.
  5. Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
  6. No geometric distortion
  7. Highly scalable, with less weight gain per increase in size (from less than 30 inches wide to the world's largest at 150 inches).
Cons:
  1. Large pixel pitch means either low resolution or a large screen
  2. Noticeable flicker when viewed at close range
  3. High operating temperature
  4. Somewhat more expensive than LCD
  5. High power consumption
  6. Only has one native resolution. Displaying other resolutions requires a video scaler, which degrades image quality at lower resolutions.
  7. Fixed bit depth
  8. Input lag
  9. Older PDPs are prone to burn-in
  10. Dead pixels are possible during manufacturing

Penetron

Pros:
  1. See-through for transparent HUDs (although LCDs are also transparent, they are not self-lighting.)
  2. Very high contrast ratios.
  3. Extremely sharp.
Cons:
  1. Color displays are limited to about four tints.
  2. Orders of magnitude more expensive than the other display technologies listed here.
Modern technology

Analog monitors
Most modern computer displays can show an infinite number of different colors in the RGB color space by changing red, green, and blue analog video signals in continuously variable intensities. These have been almost exclusively progressive scan since the middle 1980s. While many early plasma and liquid crystal displays have exclusively analog connections, all signals in such monitors pass through a completely digital section prior to display.
Computer & Analog Monitor

While many similar connectors (13W3, BNC, etc…) were used on other platforms, the IBM PCVGA connector. All of these connectors deliver nearly flawless high resolution video which vastly outclasses that of a TV. and compatible systems long ago standardized on the

Digital and analog combination
The first popular external digital monitor connectors, such as DVI-I and the various breakout connectors based on it, included both analog signals compatible with VGA and digital signals compatible with new flat-screen displays in the same connector. This made the connector nearly painless for users of both technologies.
Digital Analog Watch

Digital monitors
Newer connectors are being made which have digital only video signals. Many of these, such as HDMI and DisplayPort, also feature integrated audio and data connections. One less popular feature most of these connectors share are DRM encrypted signals, although the HDCP technology responsible for implementing the protection was necessarily rudimentary to meet cost constraints, and was primarily a barrier aimed towards dissuading average consumers from creating exact duplicates without a noticeable loss in image quality.

0 comments:

Post a Comment

Newer Post
Older Post