LCD Monitors Introduction - PowerPoint PPT Presentation

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LCD Monitors Introduction

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  1. LCD MonitorsIntroduction Jan 7 2007 David Thompson

  2. LCD Advantage + Size + power + wide screen format + Availability + Brightness LCD Difference Viewing Angle Response time (latency) Resolution (fixed) Color Gamut Color Accuracy Contrast LCD vs. CRT

  3. LCD –How it works

  4. LCD –How it works

  5. Variations Electrodes & Circuitry

  6. Variations Color Pattern

  7. TN Viewing angle Problem

  8. 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)

  9. Variation II - MVA Multi Domain Vertically Aligned Phillips Developed

  10. Variations III – PVA Pattern Domain Vertically Aligned Samsung’s variant of MVA

  11. Variations Comparison

  12. * 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: 5~:4,4,8; 6~:4,8,4,8; 7~:8,8,4

  13. Resolution

  14. Choose resolution to fit your needs • Unlike CRT, LCD resolution does not “scale” well • Low resolution + big screen >> big pixels • High resolution + small screen >> small pixels (small type, small icons etc.) • Look for a pixel pitch of about .25 - .3 mm to replicate a CRT.

  15. Buying a Monitor • Contrast - 400:1 minimum • Check for fall-off vs. viewing angle • >600:1 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

  16. Buying Cont’d • 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

  17. Buying cont’d • 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 won’t get a replacement, so don’t take it home! • Uniformity is desirable and non-uniformity is not correctable, if an area is noticeably dark, try another

  18. 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/index.html (Monitor reviews) • http://www.anandtech.com/displays/(Monitor reviews)

  19. 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)