LCD Monitors Introduction

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LCD MonitorsIntroduction

• Jan 7 2007
• David Thompson

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LCD vs. CRT

• LCD Advantage
• Size
• power
• wide screen format
• Availability
• Brightness

• LCD Difference
• Viewing Angle
• Response time (latency)
• Resolution (fixed)
• Color Gamut
• Color Accuracy
• Contrast

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LCD How it works
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LCD How it works
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Variations

• Electrodes Circuitry

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Variations

• Color Pattern

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TN Viewing angle Problem
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Variations In Plane Switching
IPS Technology employs pairs of electrodes at the
sides of each cell, running the electric field
horizontally through the material. This approach
keeps liquid crystals parallel to the front of
the panel, increasing viewing angle. (Fujitsu)
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Variation II - MVA

• Multi Domain Vertically Aligned
• Phillips Developed

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Variations III PVA

• Pattern Domain Vertically Aligned
• Samsungs variant of MVA

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Variations Comparison
TN IPS Hitachi LgPhillips MVA Fujitsu Chi Mei PVA Samsung
View Angle -- 0 --
Response (Latency) 0 -- -- - - 0 0
Contrast -- - - -- 0 0 --
Color -- -- 0 0 --
Gamma (Accuracy) --
Cost - - -
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Color Gamut Trickery

• 8 bit/ Color channel is Industry Standard
• 16.7 million colors (2563)
• 6 bit/ Color channel is typical for TN type
  displays (to improve response time)
• 262 Thousand colors (643)
• Dither schemes used to approach 16 million
• The SRGB gamut may be covered but a slice through
  it would look like Swiss cheese owing to
  missing color values. Only the values 4,8,12
  would be represented in 8 bit space, so values
  5,6,7 for example, would be approximated by
  switching between 4 8. ex 54,4,8
  64,8,4,8 78,8,4

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Resolution
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Choose resolution to fit your needs

• Unlike CRT, LCD resolution does not scale well
• Low resolution big screen gtgt big pixels
• High resolution small screen gtgt small pixels
  (small type, small icons etc.)
• Look for a pixel pitch of about .25 - .3 mm to
  replicate a CRT.

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Buying a Monitor

• Contrast - 4001 minimum
• Check for fall-off vs. viewing angle
• gt6001 is fuzzy math on part of vendor usually
  high brightness with gray blacks
• Brightness - 200 Cd/m2 is adequate
• Reference CRT 100 Cd/m2
• Video Driver Digital Video Input (DVI)
  mandatory for adjustment/calibration

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Buying Contd

• Color- If you care about color, 8bit is mandatory
  (16.7 million colors advertised does not imply
  8bit. Check the specs!
• Gamut- Does it match SRGB? At least 95 should
  be available
• Accuracy- As sold accuracy may be poor.
• Can it be corrected? LCD color is stable, so
  one- time correction may be enough for
  non-critical work

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Buying contd

• Low promotion monitors will rarely meet all the
  criteria.
• An extra 100 will generally buy much better
  performance
• Try before you buy
• Dead pixels are allowed and you wont get a
  replacement, so dont take it home!
• Uniformity is desirable and non-uniformity is not
  correctable, if an area is noticeably dark, try
  another

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References

• http//www.xbitlabs.com/articles/other/display/lcd
  -guide.html(28 pages!)
• http//www.behardware.com/ (Monitor reviews)
• http//www.tomshardware.com/graphics/displays/inde
  x.html (Monitor reviews)
• http//www.anandtech.com/displays/(Monitor
  reviews)

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Acronym Glossary

• DVI Digital Video Input (as opposed to analog
  video control)
• IPS In Plane Switching (type of display)
• ITO Indium Tin Oxide (transparent electrode)
• LCD Liquid Crystal Display
• MVA Multi-domain vertically aligned (type of
  display)
• PVA Pattern-domain vertically aligned (type of
  display)
• TN Twisted Nematic (type of display)
• TFT Thin Film Transistor ( a necessary
  component of LCDs)