LCD Technologies
by xtknight, February 26, 2007
If you're looking for an LCD, you've come to the right place. Read on if you want to pick the perfect LCD for you and your needs.
Viewing angle of ViewSonic VP930b (P-MVA)
Among the only specs you should pay attention to are the viewing angles which tip off the type of panel (120-170=TN, 176-180=VA/IPS). For viewing angles listed as 0-90 degrees, you can just double this to get the bidirectional number you're looking for.
Let's discuss the types of LCD panels available today. I would rather focus in-depth on the flaws than beautify their mediocrities and advantages, so keep in mind that this is all relative. All of the below panels use nematic liquid crystal technology.
TN (Twisted Nematic)
This type is the lowest quality of the bunch, and also the most prominent. You should expect quite a few variations in the image from uniformity and viewing angle inconsistencies. When you move your head, you will always see a slightly different image, and other details (particularly dark) of the image will be revealed at different angles. Color depth is always limited to 64 levels of brightness. Because of that, TN panels are speed demons. That is, they have a very fast image update rate, generally referred to as response time.
Ghosting on a fast TN display1
Any claims of "true 8-bit" TNs are fallacies. All TNs use dithering or frame rate control (FRC) methods to emulate the full 256 levels of brightness, and while these methods can be almost perfect, color depth is only one (small) problem of TN screens. Don't think that an "8-bit" TN will give you the quality of a properly configured, true 8-bit S-IPS panel. In fact, don't believe anything you read about how good an LCD is. These "reviews" all vary depending on past experiences and overall technical familiarity with the technology. Be skeptical of claims of "no ghosting", as even TNs have a little ghosting. It may not be noticeable to some, but others will notice it in a second if they know what to look for.
Generally, contrast on TNs is quite low, and brightness is fairly low compared to the other LCD types. Compared to a high-quality display, image quality leaves something to be desired with dark tones seeming too bright and bright ones too dark. The low contrast causes images to look faded in comparison.
What makes a TN, a TN?
The crystals of a TN panel are arranged in such a fashion that they are all pointing the same direction. When you are not viewing the panel in this direction, the image will look different (faded or "inkblotted"). Film can be added to drastically improve the viewing angles. However, the original description of TN panels above already takes the film into account. TN panels without film can be seen in older laptops with small screens, where it was less of an inconvenience.
| Panel Type | |||||||
|---|---|---|---|---|---|---|---|
| TN | VA | IPS | |||||
| Samsung | X | X | |||||
| LG Philips LCD | X | X | |||||
| AU Optronics | X | X | |||||
| Chi Mei Optoelectronics | X | X† | |||||
| Chunghwa Picture Tubes | X | X† | |||||
† TV panels only
VA (Vertical Alignment)
These mid-range panels are a nice sacrifice between TNs and IPSes. They don't have nearly the amount of uniformity or viewing angle problems that TNs do. However, they will still slightly shift in color when viewed from medium to extreme angles. Additionally, they will hide details at a perpendicular (straight-on) viewing angle because of how the crystals are arranged. The brightness on the most recent VA panels makes this not so much an issue. VA panels are technically capable of displaying 256 levels of brightness, but not all do.
Contrast on VA-type panels is stellar. White level is high and black level is very low. That doesn't make the image the best of all these types, though. For rather unknown reasons, current VA panels have a hard time producing midtones naturally. They tend to look a little over-bright. Likely it is because the color temperature regulation is less consistent than that of a good IPS panel.
Response time is by far the slowest, but as always this can be offset by using a good overdrive algorithm to use the crystal technology in the most efficient pattern.
A Brute Force Solution
VA panels avoid the viewing angle problems of TNs by adding one domain of crystals that contains four to eight crystals pointing all different directions. This is a close approximate to a perfect image in all directions.
IPS (In-Plane Switching)
I like to call these the "stable" TFT type. They have a stable role in the market, that is, in the photo-editing and high-end sectors they will always be the tops. Their image is near perfectly stable in all directions. Color reproduction and brightness regulation is the most stable of any LCD.
Unfortunately, another thing about them that is stable is the price. You'll always pay at the very least a 25% premium for this type, typically ranging from 40-60%. On the market, they are relatively rare. The cheapest, widely available 20.1" widescreen using S-IPS technology (the NEC 20WMGX2) cost $570 at the time of writing. Meanwhile, the HP LP2065, a 20.1" 4:3 screen utilizing S-IPS, cost $405 with some rebates available.2
When it comes to skin tones, IPS type panels are far ahead of others. Gamma and color regulation is amazing, the closest to a good CRT you'll ever come. Nearly all IPS panels reproduce 256 levels of brightness. Response time, with overdrive, is roughly twice as slow as TN panels, which in itself is not bad at all.
The 800lb Gorilla
The crystals in IPS panels are driven in a different fashion, causing them to stay in the same plane at all times but to still twist on one axis. This allows them to reproduce a very stable image in all directions. They still get a little darker at extreme angles, and black on them turns a dark violet at those same angles. Another caveat of IPS panels is their dark pixel lining, which contributes to the screen door effect.
LCD Subtypes
S-IPS (Super IPS): The only real type of IPS available. The description of IPS above caters to this sub-type.
AS-IPS (Advanced Super IPS): The Ferrari of LCDs. Great contrast and response time, wide viewing angles, natural skin tones, you name it... (also very expensive)
A-TW-IPS (Advanced True-White IPS), SA-SFT (Super-Advanced Super-Fine TFT): Professional IPS types with slightly-modified color filters to improve natural color reproduction. Extremely expensive.
MVA: Multidomain Vertical Alignment, usually manufactured by AU Optronics. Basically everything in the description for VA applies for these. Also named P-MVA, which uses four domains of crystals.
AMVA: Advanced Multidomain Vertical Alignment, a new panel from AU Optronics that will debut shortly. They will have further improved contrast and viewing angle characteristics. They will be paired with a barrage of new technologies like new backlights and advanced response time acceleration technology.
PVA: Patterned-ITO Vertical Alignment, typically a Samsung panel. Again, they are similar enough to MVAs that the VA description also suits them. Some PVAs are 6-bit, though 8-bit ones are known to exist.
S-PVA: Super Patterned Indium Tin Oxide Vertical Alignment (silly). S-PVAs are mostly true 8-bit and boast higher contrast than PVAs as they use eight domains of crystals, versus PVA which uses four.
B-TN ("Best TN"): Simply Samsung's latest TN technology. Arguably, the best TNs really come from LG Philips.
Which is Best for Me?
Number crunchers and clerks are best suited to VA panels due to their nice bright appearance and minimal screen door effect. MVAs come at a price anyone can afford as long as you find the right model. Their wide viewing angle will make office work a pleasure. That doesn't mean IPS screens aren't just as good for this purpose, but they generally come at a higher price. Also, if you notice the screen door effect, they could make prolonged usage painful. The lower brightness IPS panels don't have nearly the problem as the high brightness ones, such as the AS-IPS variant NEC 20WMGX2.
Photo editors will want to stick with the tried-and-true IPS panels. If the price is simply too high for you, VA panels being 8-bit and high-contrast aren't a bad alternative. However, you won't get the natural colors of a quality IPS screen, especially if you leave your display uncalibrated. Be sure to properly adjust the LCD for the angle you're viewing at, as MVA screens have multiple domains and detail is hidden at a perpendicular angle.
Which leaves us with...TNs. These types of panels are for hardcore gamers who want the absolute minimum response time. As you should know, contrast and viewing angles will suffer with these types. The best part of TNs is how affordable they are, but that also means you'll have to choose carefully to avoid low quality panels.
Dodging the Bullets
If you've learned anything from the above reading, it's that the LCD situation is far from perfect. Therefore, you want to look towards the highest quality panels you can get which are usually in 20" and above panels. There are a couple exceptions, such as the P-MVA in the 19" ViewSonic VP930b, and the S-PVA Samsung 971P. The situation is much better with the biggest panels, as TN panels become unsuitable for everybody at 23" or larger. No LCD is going to be perfect, so just like every other technology, you are avoiding the potential downfalls of certain models in favor of others. The best thing to do is just to pick one and be happy with what you get. Don't spend endless hours researching one particular model as you may come across flaws you may not have even noticed otherwise! The more popular an LCD is, the more information there will be about its flaws. What you don't hear about is how much worse the other models are, so compelled as you may be to drift away from a highly-esteemed (but also -critiqued) LCD, don't give in.
References
1 LesNumeriques.com "Face to Face", http://img1.lesnumeriques.com/produits/35/1413/35_127_109.jpg
2 Newegg.com,
NEC Display Solutions 20WMGX2 Silver 20.1" 6ms DVI Widescreen LCD Monitor 470 cd/m2 1600:1 Built in Speakers - Retail
HP LP2065 Silver-Carbonite 20.1" 8ms DVI LCD Monitor with Height & Pivot Adjustments 300 cd/m2 800:1 - Retail