LCD MonitorsIntroduction

Jan 7 2007

David Thompson

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

LCD –How it works

LCD –How it works

VariationsElectrodes & Circuitry

VariationsColor Pattern

TN Viewing angle Problem

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)

Variation II - MVAMulti Domain Vertically Aligned

Phillips Developed

Variations III – PVAPattern Domain Vertically Aligned

Samsung’s variant of MVA

Variations ComparisonTN 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 $-$$ $$$$ $$-$$$ $$-$$$

* 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

Resolution

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.

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

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

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

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)

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)