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Written by Olin Coles, David Ramsey & Vito Cassisi   
Wednesday, 15 September 2010
Table of Contents: Page Index
Choosing the Best LCD Panel Technology
LCD Technology
How LCD Panels Work
Contrast Ratio, Viewing Angle, and Surface Finish
Color/Bit Depth
LCD Resolution and Scaling
LCD Panel Image Processing
3D LCD Technology
Connections and Content Protection
LCD Summary and Recommendations

Color/Bit Depth

Bit depth is the number of bits used to 'describe' the color of a particular pixel, also known as 'bits per pixel'. A bit depth of 24-bits is often referred to as 'truecolor', and is accepted as a high quality representation of colors within a given RGB gamut. 24-bits allows for 224 colors to be represented (that's 16,777,216 different colors)! As you'd expect, bits are just data, and when it comes to color, humans can't see data unless it's first converted to light via a monitor such as a LCD panel. Not all panels are created equal, however.

As we've discussed previously, there are many different panel types, including but not limited to TN, VA and IPS. Twisted Nematic panels are regarded as the lowest-grade of the lot, and for good reason. Generally, a TN panel can only produce 6-bits of color per RGB subpixel. That is, 6-bits for red, 6-bits for green and 6-bits for blue. When combined, this gives a total of 218 (262,144) unique colors, which is equivalent to 18-bits per pixel. Clearly this is vastly inferior to the 16+ million colors of an 8-bit panel which can display 8-bits per subpixel for a total of 24-bit truecolor. But surely a panel with 64x fewer colors would look horrible? This is where the trickery that is dithering comes into play.

Dithering is often used on 6-bit panels to produce truecolor images. Dithering can produce extra colors by tricking the human eye via processes such as flickering between two colors to produce an intermediate color, and using a halftone-esque technique such as a checkerboard pattern. Variations of the latter are often used.

dithering.png

But how does one determine the bits per subpixel of a given panel? Well, it's not easy, since all modern panels claim to produce millions of colors. Fortunately, there are ways to spot the difference, including:

  • 16.2 million vs 16.7 million colors. The former indicates a dithered panel. The latter may or may not be.
  • Panel type. TN panels are dithered, VA and IPS panels are generally native 8-bit.
  • Fast response times tend to be limited to 6-bit panels. You're not going to find 2ms 8-bit panels at this point in time.
Although 6-bit panels sound dodgy, they do have a speed advantage for fast-paced games and movies. Dithering tends to do well in modern LCD monitors, such that trying to distinguish between a 6-bit and 8-bit panel can be difficult without direct comparison. The main reason for purchasing an 8-bit panel is color accuracy when working with graphic software, so unless your line of work is color sensitive, the price and response time may be off-putting.



 

Comments 

 
# RE: Choosing the Best LCD Panel TechnologyDoug 2010-09-15 22:47
A very good overview and more. I would suggest these two links to better clarify TN and IPS and it's variations and to check which panel your monitor or prospective monitor has:

Panel Types and Benefits:
TFT Central (##tftcentral.co.uk/articles/panel_technologies.htm)
Panel Type (##tftcentral.co.uk/articles/panel_technologies.htm)
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# SED and FEDSteve 2010-09-16 09:20
One day SED and FED TV's and monitors will dominate, if only cannon (SED) and sony/AU Optronics (FED) can get manufacturing prices and legal issues out of the way.
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# Great summaryBernardP 2010-09-17 06:11
... and objectively written too. May I add that any large screen TV buyer should make sure to also look at plasma sets? ;-)

Also, regarding monitors, NVidia video drivers allow for creation and proper scaling of custom resolutions. This gives very good results and gets around limitations in the monitor's built-in scaler. Unfortunately, with ATI/AMD, resolution choices are limited to those the monitor natively supports.

Being able to display and properly scale a lower resolution is useful for no-longer-young eyes that have trouble with the high pixel pitch on, for example, a 23-inch 1920x1080 monitor.
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# 720P and 1080iJames 2010-09-24 11:40
You stated "given the fact that 720P and 1080i images have different aspect ratios"

This is not true, the ATSC television standard is 16:9 aspect ratio, also known as 1.78:1. 1080i is no different than 1080p except that with interlace, every other scan line is drawn per 1/60th of a second - in progressive scan the entire frame is drawn every 1/60th of a second. All the HD/ATSC formats are the same aspect ratio. The overall frame shape remains the same among them all. Some wide-screen computer panels (and a few odd tvs) come in 16:10 aspect ratios, which may be the source of your confusion, but in all cases the correct aspect ratio for HDTV is 16:9, and it is the only aspect ratio specified by ATSC.
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# RE: 720P and 1080iJames 2010-09-24 11:56
Tvtechnology.com is the leading trade magazine for people in the industry, so if you don't believe me, check around. But a calculator can also solve this. 1280/720 = 1.78. 1920/1080 = 1.78.
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# Time for an update versionNehemoth 2012-05-18 16:52
What about if you update this amazing post?
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# Update, due to a DIY Project(or)Medenyx 2012-07-13 12:57
Can't agree more with Nehemoth.
Me, ... , well, I am trying to build a 3D (shutter!) DIY projector, and I am in a trouble to find 120Hz 15.4" (or max 15.6") LCD with its corresponding LCD Controller, with a proper DVI input, that comes in a dual link version, not to mention HDMI, VGA & the other possible (older, analog) inputs, all in the same separate / independent panel. An RF digital TV tuner, and a remote would be nice, too. ;-D
nVidia's solution is almost perfect!, but where to find a WUXGA 1920x1200 (6->8 bit) LCD 3D 120Hz Display?
I am open to any positive suggestion. Especially if it is not the most expensive one!
If you have any, thanks in advance!
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