IPS
IPS stands for 'In Plane Switching' which was originally developed by Hitachi in 1996. This original version had some obvious limitations and has been through several generations sinces its initial development. It was produced to combat the two main issues with TN matrices, those being limited viewing angles and low-quality colour reproduction. As already stated, the main manufacturer of IPS technology today is LG.Display (prev LG.Philips)
S-IPS
'Super IPS' was the first major development in IPS technology, helping to overcome some of the original drawbacks and now offering some improved response times and lower production costs. You will still see S-IPS mentioned in modern displays (e.g. HP still refer to their LP2475W as having an S-IPS panel on their website) and LG.Display still refer to their technology as S-IPS on their website in many cases. This is probably still the most generic name used for IPS panels in the market.
AS-IPS
'Advanced Super IPS' hasn't really been seen much, but was used by NEC to promote their NEC 20WGX2 when it was launched. This was supposedly a custom made and tweaked panel produced by LG.Display exclusively for the 20WGX2, and it was characterised by an excellent response time, something which was really a first in the IPS market.
H-IPS
A newer generation of S-IPS panels, this time with a slightly different pixel alignment and setup giving rise to the name 'Horizontal IPS'. Pixels are orientated in straight vertical lines with a slightly smaller electrode width. Close inspection of modern IPS panels can show this new H-IPS pixel structure, although not all manufacturers refer to their models as featuring an H-IPS panel. Indeed, LG.Display don't really make reference to this H-IPS version, although from a technical point of view, most modern IPS panels are H-IPS in format. NEC have referred to H-IPS in their recent panel specs for models such as the 2690WXUi2 and 3090WUXi.
e-IPS
This is perhaps the most confusing of the 'new' versions of IPS panel being used today. It's not really been clarified, and the 'e' seems to be a bit of a mystery. Back in 2005, LG.Display talked about the improvements they were making with their latest generation of 'Enhanced IPS' panels , mostly relating to the overdriving circuitry they were now using to boost response times. This was some time ago, and the name e-IPS (or should that have been E-IPS?) was never really widely used. We saw the AS-IPS panel in the NEC 20WGX2 which seemed to be offering the same improvements, and then H-IPS became more of a widespread name for the newer generation of panels. These new H-IPS panels featured fast response times and the presence of RTC, so perhaps LG.Display didn't bother with the E-IPS name too much.
More recently though, the Dell 2209WA was the first IPS-based model to be released in the 22" market and advertised as featuring an e-IPS panel. The very competitive and low cost lead some to speculate that the 'e' stood for 'economy IPS'. There seems to have been a fair amount of use of this new 'e-IPS' name with other manufacturers such as NEC using it in their specifications for their new 2490WUXi2 for instance. They have even made the distinction and used H-IPS in other models in their range (e.g. 2690WUXi2).
The name 'economic IPS' seems to make the most sense, although it could also be linked to 'enhanced' and perhaps even 'energy efficient' or 'eco' with all the modern focus on carbon footprints and power consumption. It is a sub-section of H-IPS panels really but used in lower cost displays as these panels are less expensive to manufacturer. Some are actually 6-bit + AFRC modules in fact (as opposed to true 8-bit) which might explain how the costs are kept very low in some cases.
UH-IPS and H2-IPS
These are new names which some manufacturers such as HP and LG seem to be touting a little. They has been mentioned with the launch of the HP ZR24w and ZR22w models for instance, along with LG's line of IPS LED screens (e.g. IPS226V). HP have stated that these 'new' panels offer improved energy efficiency, but it's unclear what the new letters stand for. Perhaps the 'UH-IPS' stands for 'Ultra Horizontal-IPS'? It certainly seems these are just slightly updated versions of H-IPS panels, with HP playing on a certain key message or characteristic with their description. It's possible as well that UH-IPS is just the same thing as e-IPS, with different manufacturers using different terminology to try and separate their displays. I suspect that UH-IPS is either the same thing as e-IPS, or a sub-category of that development, which in turn is a sub-category of H-IPS.
Some spec sheets from LG give some clues as to the differences. The lines separating the subpixels are smaller than with H-IPS and therefore the UH-IPS technology has an 18% higher aperture ratio. This will supposedly improve brightess and enhance contrast, all while allowing them to save energy. LG have used this terminology with their LED backlght models.
S-IPS II
Another new term being used by LG for some of their modern IPS LED screens such as the IPS236V. This "S-IPS II" reportedly has an even higher aperture ratio than UH-IPS (11.6% higher), further improving brightness and contrast and helping save energy. This particular IPS236V is again combined with LED backlighting. It looks also from the information available (above) that the pixel structure has been altered and is no longer vertical as with H-IPS, but more like the traditional S-IPS / AS-IPS "arrow" layout. This looks more like an e-IPS type development, but returning to the older S-IPS pixel layout as opposed to developing H-IPS.
p-IPS
This is a new name which NEC have started to talk about since early 2010 with their new PA series of screens. Thankfully they've been kind enough to tell us what the 'p' stands for in their marketing, giving rise to the generation of 'Performance IPS' panels. This new panel name is being used in the new 24" - 30" sized screens (PA241W, PA271W and PA301W). In fact the p-IPS name is just a sub-category of H-IPS technology, being created as a way for NEC to distinguish their new "10-bit" models from the rest of their range. In addition, when you look into the details of it the panels are actually an 8-bit module with 10-bit reciever, giving you an 8-bit+AFRC module. This is capable of producing a 1.07 billion colour palette (10-bit) through FRC technology but it is not a true 10-bit colour depth.
There are very few true 10-bit panels out there in the market, although a 24" 10-bit module was features in the HP LP2480zx for instance, but at a much higher cost. Some other high end models use true 10-bit panels as well, but you need to be a little wary of manufacturers specified 10-bit figures as they are not always 100% accurate.
It's all very well saying a panel is capable of 10-bit colour depth (1.07 billion colour palette) as opposed to an 8-bit colour depth (16.7 million colours), but you need to take into account whether this is practically useable and whether you're ever going to truly use that colour depth. Apart from the requirements of your application, operating system, graphics card and software, one more pertinent limitation is from a display point of view, where there must be an interface which can support 10-bit colour depth. At the moment DisplayPort and Dual-link DVI are the only options which can. A full 10-bit work flow is still extremely uncommon in the current market.
Regardless of whether you have a true 10-bit colour depth being displayed, a screen with 10-bit capabilities still has its advantages. The monitor should still be capable of scaling the colours well, even from 24-bit sources. Most of these 10-bit panels will also be coupled with extended internal processing which will help improve accuracy and these are better translated onto a 10-bit panel than they would be onto an 8-bit panel, giving less deviation and less chance of banding issues.
Asus have also adopted the "p-IPS" name in their recent 24" PA246Q model, which again is an IPS based screen with "10-bit" colour support. It is not only NEC who are using this new name to distinguish the models using these new panels. Some manufacturers have utlised the same 10-bit panels in their screens but have not used the p-IPS name, and stuck with IPS or sometimes S-IPS instead (e.g. Dell U2410, U2711, U3011).
