TN Film, MVA, PVA and IPS Explained
Simon Baker, updated 30 April 2011
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TN Film (Twisted Nematic + Film)
TN Film panels are the mostly widely used in the TFT market, with smaller sized screens (15", 17" and 19") being almost exclusively limited to this technology. Some other sectors are dominated almost entirely by this technology as well, including the 22" market, and the technology is quickly creeping into the larger screen sizes of 23 - 28". The TN Film panels are made by many different manufacturers, with the big names all having a share in the market (Samsung, LG.Display, AU Optronics) and being backed up by the other companies including CMO, CPT etc.
TN Film has always been so widely used because it is comparatively cheap to produce panels based on this technology. As such, manufacturers have been able to keep costs of their displays down by using these panels. This is also the primary reason for the technology to be introduced into the larger screen sizes, where the production costs allow manufacturers to drive down retail costs for their screens and compete for new end-users.
The other main reason for using TN Film is that it is fundamentally a responsive technology in terms of pixel latency, something which has always been a key consideration for LCD buyers. It has long been the choice for "gamers" screens and response times have long been, and still are today, the lowest out of all the technologies (at least on paper). Response times typically reach a limit of around 5ms at the ISO quoted black > white value, and as low as 1ms across grey to grey transitions with Response Time Compensation. TN Film is also the first panel technology being incorporated into the new generation of true 120Hz desktop displays, pairing low response times with high refresh rates for even better moving picture and gaming experiences, improved frame rates and 3D content support.
The problem with TN Film is that viewing angles are pretty restrictive, especially vertically, and this is evident by a characteristic severe darkening of the image if you look at the screen from below. Contrast and colour tone shifts can be evident with even a slight movement off centre, and this is perhaps the main drawback in modern TN Film panels. Some TN Film panels are better than others, but they are still far more restrictive with fields of view than other panel technologies.
Movie playback is often hampered by 'noise' and artefacts, especially where RTC is used. Black depth was traditionally quite poor on TN Film matrices due to the crystal alignment, however, in recent years, black depth has improved somewhat and is generally very good on modern screens, even competing with some VA matrices and normally surpassing IPS based screens. TN Film is only a true 6-bit colour panel technology, but is able to offer a 16.2 million, and now even a 16.7 million, colour palette thanks to dithering and Frame Rate Control methods.
Many modern TN Film panels are now being paired with W-LED (White LED) backlighting for improved energy efficiency, slim profile and as part of the latest market trend.
Vertical Alignment (VA)
VA technology was first developed by Fujitsu in 1996. Small viewing angles were its main disadvantage. This problem was solved by dividing each pixel into domains which worked synchronously. This lead the birth of….
Multidomain Vertical Alignment (MVA)
MVA technology, was later developed by Fujitsu in 1998 as a compromise between TN Film and IPS technologies. On the one hand, MVA provided a full response time of 25 milliseconds (that was impossible at the time with IPS, and not easily achievable with TN), and on the other hand, MVA matrices had wide viewing angles of 160 - 170 degrees, and thus can compete with IPS in that parameter. The viewing angles are also very good in the vertical field (an area where TN panels suffer a great deal) as well as the horizontal field. MVA technology also provides high contrast ratios and good black depth, which IPS and TN Film couldn't quite meet at the time.
In MVA panels, the crystals in the domains are oriented differently, so if one domain lets light pass through, the neighbouring domain will have the crystals at an angle and will shutter the light (of course, save for the display of white color, in which case all the crystals are placed almost in parallel to the matrix plane).
The problem with MVA panels was
that traditionally the response time was not as good as TN film panels. Sadly,
the response time grows dramatically when there’s a smaller difference between
the pixel’s initial and final states (i.e. G2G transitions). Thus, such matrices are
unsuitable for dynamic games. Of course, “suitability” is
subjective, and some people may be quite satisfied with the image
produced by an MVA matrix, but they are objectively slower than TN as well as
IPS matrices anyway.
With the introduction of RTC and overdrive
technologies, the manufacturers launched a new breed of....
Premium MVA panels (P-MVA) and Super MVA (S-MVA)
Premium MVA from AU Optronics, and Super MVA (S-MVA) from Chi Mei Optoelectronics and Fujitsu. These offer improved response times across grey to grey (G2G) transitions which is a great improvement in the MVA market. While responsiveness is still not quite as fast as TN film panels using similar RTC technologies, the improvement is obvious and quite drastic.
The color-reproduction properties of the MVA technology proved to be deficient too. Such panels give you vivid and bright colors, but due to the peculiarities of the domain technology many subtle color tones (dark tones often) are lost when you are looking at the screen strictly perpendicularly. When you deflect your line of sight just a little, the colors are all there again. This is a characteristic VA panel contrast shift (sometimes referred to as 'black crush' due to the loss of detail in dark colours) and some users pick up on this and might find it distracting. Thus, MVA matrices are somewhere between IPS and TN technologies as concerns color reproduction and viewing angles. On the one hand, they are better than TN matrices in this respect, but on the other hand the above-described shortcoming prevents them from challenging IPS matrices, especially for colour critical work.
Traditionally MVA panels offered 8-Bit colour depth (a true 16.7 million colours) which is still common place today. We have yet to see any new breed of "10-bit" MVA panel. Black depth is a strong point of these P-MVA /S-MVA panels, being able to produce good contrast ratios as a result. These were originally superior to TN Film but have been surpassed with modern TN Film, and even IPS, matrices.
MVA panels also offer some
comparatively good movie playback with noise and artifacts quite low compared
with other technologies. The application of overdrive doesn't help in this area,
but MVA panels are pretty much the only ones which haven't suffered greatly in
movie playback as a result. Many of the MVA panels are still pretty good in this
area, sadly something which overdriven TN Film, IPS and PVA panels can't offer. While
CMO are still manufacturing some S-MVA matrices, AU Optronics no longer produce
P-MVA panels and instead produce their newer generation of MVA, called AMVA (see
Advanced MVA (AMVA)
AU Optronics have more recently been working on their latest generation of MVA panel technology, termed 'Advanced MVA' (AMVA). This is designed to offer improved performance including reduced colour washout, and the aim to conquer the significant problem of color distortion with traditional wide viewing angle technology. This technology creates more domains than conventional multi-domain vertical alignment (MVA) LCD's and reduces the variation of transmittance in oblique angles. It helps improve color washout and provides better image quality in oblique angles than conventional VA LCD's. Also, it has been widely recognized worldwide that AMVA technology is one of the few ways to provide optimized image quality through multiple domains.
In addition, AMVA provides an extra-high contrast ratio of greater than 1200:1 (reaching 3000:1 at time of writing) by optimized color-resist implementation and a new pixel design. The result is a more comfortable viewing experience for the consumer, even on dimmer images. This high contrast technology can also achieve wide viewing angles of up to 178 degrees. AMVA, which the Company believes to be the most competitive solution in low color washout technology, has been applied to AUO TV panels ranging from 32" up to 42", and has attracted widespread attention among global brand-name TV customers in the United States, Europe and Japan.
AMVA still has some limitations however in practice, still suffering from the off-centre contrast shift you see from VA matrices. Viewing angles are therefore not as wide as IPS technology and the technology is often dismissed for colour critical work as a result. Contrast ratios are capable of being very high, but it seems many desktop monitors have only average contrast ratio performance comparable to older P-MVA and modern TN Film panels, and not surpassing PVA matrices. Some more recent AMVA modules are paired with W-LED backlighting and do offer some staggering static contrast ratios of >3000:1 though. Response time remains competitive and in line with the developments made with the P-MVA generation of panels. However, it does not appear to be as reactive as some overdriven TN Film and IPS matrices when it comes to pixel response times.
Fujitsu - Super High Quality MVA (June 1999)
AU Optronics AMVA Press Release
AU Optronics AMVA Technology and Product Information
PVA Technology (Patterned Vertical Alignment)
PVA was developed by Samsung as an alternative to MVA. The parameters and the development methods for PVA and MVA are so different that PVA can be truly regarded as an independent technology.
The liquid crystals in a PVA matrix have the same structure as in a MVA matrix – domains with varying orientation of the crystals allow keeping the same color, almost irrespective of the user’s line of sight and viewing angle. Viewing angles are not perfect though, as like with MVA matrices when you are looking straight at the screen, the matrix “loses” some shades, which return after you deflect your line of sight from the perpendicular a little. This 'off-centre' contrast shift, or 'black crush' as it is sometimes referred to as, is the reason why some colour enthusiasts prefer IPS based screens.
Tthere was the same problem with traditional PVA matrices as with MVA ones – their response time grew considerably when there’s a smaller difference between the initial and final states of the pixel. Again, PVA panels were not nearly as responsive as TN film panels. With the introduction of MagicSpeed (Samsung's overdrive / RTC), response times have been greatly improved and are comparable to MVA panels in this regard on similarly spec-ed panels. They still remain a little behind TN Film panels in gaming use, but the overdrive really has helped improve in this area.
The contrast ratio parameter is really good with PVA technology though. First, PVA matrices are manufactured by Samsung alone, so there can’t be any variation in quality between different manufacturers. Second, Samsung is actively working to improve the contrast ratio and with some results already: monitors with PVA matrices (they mostly come from Samsung, too) typically have a contrast ratio of anywhere between 600:1 and 1500:1 (static, not dynamic). Generally speaking, PVA matrices are the only matrix type today for which the declared contrast values are often true and sometimes the real characteristic is even better than specified. Black depth is good, and again they offer much better measurements in this area than TN Film and IPS. MVA and IPS are improving, but tend to be a little more exaggerated on paper than PVA which are generally quite reliable in this spec.
Overall, PVA matrices could be said to be an improved version of MVA. Without any new defects, save for those already present in the MVA technology, PVA matrices feature slightly improved viewing angles, better contrast ratios and a much more predictable production quality due to their being manufactured on the facilities of one manufacturer only. Movie playback is perhaps one area which is a weak point for PVA, especially on Samsung's overdriven panels. Noise and artefacts are common unfortunately and the panels lose out fo MVA in this regard.
All images in PVA section courtesy of Samsung website. Take with a pinch of salt as they are promoting their technology of course
Super Patterned Vertical Alignment (S-PVA)
Most of these are based on the introduction of “Magic Speed” (the Samsung specific RTC), which offer improved response times over traditional PVA matrices. Note that some PVA panels still used this technology, but S-PVA panels almost certainly feature it. Like P-MVA panels, these are really just an extension of the existing technology, but with the MagicSpeed technology, they have managed to make them more suitable for gaming than the older panels. One other difference is that the liquid crystal cell structure is a boomerang shape, splitting each sub pixel into two different sections with each aligned in opposite directions. This is said to help improve viewing angles and colour reproduction when viewed from the side.
While traditionally S-PVA panels offered 8-bit colour depth, there is now talk of a new generation of 10-bit panels. This article will be updated when more information is available.
S-PVA Pixel Structure
Full brightness Low brightness
Close up inspection of the pixels making up an S-PVA matrix reveals the above. The dual subpixels consist of two zones, A and B, with one being turned on only at high brightness. So, the first picture shows red subpixels of roughly rectangular shape while the second picture shows two small pieces that represent one zone of each subpixel, the second zone being completely turned off.
It is this two-zone structure that differentiates S-PVA from older PVA matrixes which used to have a monolithic subpixel divided into four domains. An S-PVA matrix has two zones with four domains in each, for a total of eight domains per each subpixel. This helps fight the gamma shift effect which occurs when not only the contrast ratio but also the gamma (i.e. the correlation between the video signal sent to the monitor and the resulting screen brightness) changes when the screen is viewed from a side. The pixel zones of S-PVA matrixes have such shape, position and voltage (in the most expensive matrixes that are installed into some TV-sets, the two zones of one subpixel can even be controlled independently) as to mutually compensate the gamma shift effect for each other. Unfortunately, the gamma shift effect is not absolutely eliminated even in S-PVA matrixes. Besides, these matrixes have one more difference from PVA. Their viewing angles are asymmetric: the gamma shift is bigger from one side.
Images and some text courtesy of X-bit Labs
Further reading: Samsung Whitepaper - PVA and S-PVA
In late 2009 Samsung started to produce their latest generation of so called cPVA panels. These new panels featured a simpler sub-pixel structure in comparison with S-PVA, but allowed Samsung to produce the panels at a lower cost, and drive down the production cost of their new screens. It's unclear what the "c" stands for. This is a similar approach to e-IPS which we discuss a little later on.
In practice, cPVA do not look any worse than S-PVA panels and in fact offer even better contrast ratios in early cPVA panel tests. Other performance characteristics including the off-centre contrast shift remained the same as S-PVA panels. Some cPVA panels are in fact using Frame Rate Control to produce their 16.7m colour depth as opposed to true 8-bit panels. See the following news piece for more information about these 6-bit + AFRC cPVA panels.
cPVA Pixel Structure
Full brightness Low brightness
If you refer to the pixel structure in the S-PVA section above you will see a difference here when cPVA subpixels are inspected close up. As you can see, there is no sign of the subpixel being divided into zones. It is monolithic at any brightness. Besides, the subpixel has very uniform brightness. Particularly, it does not have the dark dot in the center which can be seen in the photo of the S-PVA. This is returning to the older PVA structure of one zone, and 4 domains. Practical tests reveal that this cPVA structure doesn't seem to impact gamma or colour tone shift compared with S-PVA structure which is positive. An example of a cPVA based screen is the Samsung F2380.
Images and some text courtesy of X-bit Labs
In Plane Switching (IPS)
IPS technology was developed by Hitachi in 1996 to solve the two main limitations of TN-matrices at the time, those being small viewing angles and low-quality color reproduction. The name In-Plane Switching comes from the crystals in the cells of the IPS panel lying always in the same plane and being always parallel to the panel’s plane (if we don’t take into account the minor interference from the electrodes). When voltage is applied to a cell, the crystals of that cell all make a 90-degrees turn. By the way, an IPS panel lets the backlight pass through in its active state and shutters it in its passive state (when no voltage is applied), so if a thin-film transistor crashes, the corresponding pixel will always remain black, unlike with TN matrices.
IPS matrices differ from TN Film panels not only in the structure of the crystals, but also in the placement of the electrodes – both electrodes are on one wafer and take more space than electrodes of TN matrices. This leads to a lower contrast and brightness of the matrix.
We will talk about the characteristics of IPS matrices in the following sections.
The original IPS technology became a foundation for several improvements: Super-IPS (S-IPS), Dual Domain IPS (DD-IPS), and Advanced Coplanar Electrode (ACE). The latter two technologies belong to IBM (DD-IPS) and Samsung (ACE) and are in fact unavailable in shops. The manufacture of ACE panels is halted, while DD-IPS panels are coming from IDTech, the joint venture of IBM and Chi Mei Optoelectronics – these expensive models with high resolutions occupy their own niche, which but slightly overlaps with the common consumer market. NEC is also manufacturing IPS panels under such brands as A-SFT, A-AFT, SA-SFT and SA-AFT, but they are in fact nothing more than variations and further developments of the S-IPS technology.
Super-IPS panels are mostly produced by LG.Display (previously LG.Philips) and have gone through several generations since their inception. Initiall S-IPS built upon the strengths of IPS by employing an advanced “multi-domain” liquid crystal alignment. The term S-IPS is still widely used in modern screens, but technically there may be subtle differences making them S-IPS, e-IPS, H-IPS, or p-IPS for example.
Images from LG.Display website, so take with a pinch of salt when comparing with VA!
S-IPS panels have gained the widest recognition, mostly due to the efforts of another joint venture LG.Philips LCD (now known as LG.Display), which is outputting rather inexpensive and high-quality 19" - 30" matrices. Besides the high price, the response time was among the serious drawbacks of the IPS technology – first panels were as slow as 60ms on the “official” black-to-white-to-back transitions (and even slower on grey-to-grey ones!). Fortunately, the engineers dragged the full response time down to 25 ms and then 16ms later, and this total is equally divided between pixel rise and pixel fall times. Moreover, the response time doesn’t greatly grow up on black-to-gray transitions compared to the specification, so some older S-IPS matrices could challenge TN Film panels in this parameter (before overdrive anyway).
For a while, S-IPS panels remained at ~16ms as their best response time on paper. However, overdrive has caught up with this technology (what LG.Display call ODC - Over Driving Circuitry) after it's success with TN Film, PVA and MVA panels. IPS has re-emerged in recent years offering some excellent quoted response times as well as excellent responsiveness in practice. Some modern IPS panels are even as responsive as the fastest TN Film panels in real use!
Demonstration of viewing angles on IPS vs VA matrices
Images from LG.Display website, so take with a pinch of salt when comparing with VA!
The IPS technology has always been at the top end when it comes to colour reproduction and viewing angles. Colour accuracy has always been a strong point, and even in modern displays the IPS matrices can surpass the performance of TN Fillm and VA equivalents. The viewing angles are also a key part in this, since IPS matrices are free of the off-centre contrast shift that you can see from VA type panels. This is the reason why IPS is generally considered the preferred choice for colour critical work and professional colour displays, combining the excellent colour accuracy with truly wide viewing angles (178/178). S-IPS panels can show a purple colour when viewing dark images from a wide angle, and in some cases an extra (and pretty rare) film is added to the panel to improve blacks from an angle. This "Advanced True Wide" (A-TW) polarizer is not commonly used, but can be found on some NEC higher end models for instance.
The only real problem of the S-IPS technology traditionally was the low contrast ratio. This would mean you see a dark gray instead of pure black. That’s not noticeable in daylight, but if you’re working in a dimly lit room, you may be disappointed at the highlighting of the black color (coupled with the characteristic violet hue when you’re viewing the screen from a side). Black depth was often a problem with S-IPS panels. However, these have been improved significantly, and contrast ratios are now much better as a result. Whether or not black depth is as good as PVA / MVA panels is debatable, but technologies like Digital Fine Contrast DFC (dynamic contrast ratio control) are helping to make blacks better as well in multimedia applications. One area which remains problematic for modern IPS panels is movie playback, again with noise being present, and only accentuated by the heavy application of overdrive technologies.
Moving Picture Image Sticking (MPIS) - S-IPS panels do not show any image sticking when touching a moving image. On the other hand severe image sticking happens in VA panel and lasts after the image is changed for a short time.
Enhanced and Advanced S-IPS (E-IPS and AS-IPS)
Sometimes you will see these terms being used, but S-IPS is still widely used as an umbrella for modern IPS panels. With the introduction of RTC technologies (Overdrive Circuitry - ODC) and dynamic contrast ratios, LG.Display started to produce their so called "Enhanced IPS" (E-IPS, not to be confused with e-IPS) panels. Pixel response times were reduced across G2G transitions to as low as 5ms, and dynamic contrast ratios ranged up to 1600:1 initially.
Enhanced S-IPS builds on S-IPS technology by providing the same 178° viewing angle from above and below and to the sides, and greatly improves the off-axis viewing experience by delivering crisp images with minimal color shift, even when viewed from off-axis angles such as 45°. You will rarely see this E-IPS term being used to be honest.
You may also occasionally see the name "Advanced S-IPS" (AS-IPS) being used, but this was just a name given specifically by NEC to the E-IPS panel developed and used in their very popular NEC 20WGX2 screen.
Cleverdis - E-IPS Website Article
Enhanced Super IPS Whitepaper (LG.Philips Dec 2005)
In the more recent generations of IPS panel, LG.Display have altered the pixel layout giving rise to 'Horizontal-IPS'(H-IPS) panels. In simple terms, the manufacturer has reportedly reduced the electrode width to reduce light leakage, and this has in turn created a new pixel structure. This structure features vertically aligned sub-pixels in straight lines as opposed to the arrow shape of S-IPS panels.
In practice, it can be quite hard to spot the difference, but close examination can reveal a less 'sparkly' appearance and a slightly improved contrast. Some users find a difference in text appearance as well relating to this new pixel structure but text remains clear and sharp. H-IPS will also often show a white glow from a wide angle when viewing black images, as opposed to the purple tint from S-IPS matrices. Some IPS panels in high end displays are coupled with an Advanced True Wide (A-TW) polarizer which helps improve black viewing angles and reduce some of the pale glow you can see at wide angles on IPS panels. However, this A-TW polarizer is not included in every model featuring H-IPS and this should not be confused. It is very rarely used nowadays unfortunately.
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. As an example of someone who has referred to this new generation, NEC have used the H-IPS name in their recent panel specs for models such as the 2690WXUi2 and 3090WUXi.
The following technical report has feedback from the LG.Philips LCD laboratory workers: "We designed a new pixel layout to improve the aperture ratio of IPS mode TFT-LCD(H-IPS).This H-IPS pixel layout design has reduced the width of side common electrode used to minimize the cross talk and light leakage which is induced by interference between data bus line and side common electrode of conventional IPS mode. The side common electrodes of a pixel can be reduced by horizontal layout of interdigital electrode pattern where conventional IPS pixel designs have vertical layout of interdigital electrodes. We realized 15 inch XGA TFT LCD of H-IPS structure which has aperture ratio as much as 1.2 times of corresponding conventional IPS pixel design." ©2004 Society for Information Display
S-IPS Pixel Structure
Above: S-IPS structure taken from LM300WQ3-STA1 panel. Image credit to Kurtd
H-IPS Pixel Structure
Above: H-IPS structure taken from LM240WU4 panel. Image credit to Kurtd
Above: Evolution of IPS as detailed by Hitachi Displays: "IPS technology was unveiled by Hitachi, Ltd. in 1995, and put to practical use in 1996. Since then, it has evolved into Super-IPS, Advanced-Super IPS, and IPS-Pro."
During 2009 LG.Display began to develop a new generation of e-IPS panels which is a sub-category of H-IPS. They simplifed the subpixel structure in comparison with H-IPS (similar to cPVA vs S-PVA) and increased the transparency of the matrix. In doing so, they have managed to reduce production costs significantly, aiming to compete with the low cost TN Film panels and Samsung's new cPVA generation. Because transparency is increased, they are able to reduce backlight intensity as you need less light to achieve the same luminance now. This helps keep costs down significantly compared with S-IPS.
The main drawback of e-IPS in comparison with S-IPS is that the viewing angles are smaller. When you take a look at an e-IPS matrix from a side, the image will lose its contrast as black turns into gray. On the other hand, there is no tonal shift (as with TN and cPVA matrixes) and the viewing angles, especially vertical ones, are still much larger than with TN. By the way, the contrast drop occurring when the screen is viewed from a side can be compensated by means of special correcting film (A-TW polarizer), but as e-IPS matrices are meant for midrange monitors and this film costs money, most products come without it. 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.
Although it's unknown what the "e" stands for here, it's likely that it means "economic" or similar, since these new panels are all about trying to keep production and retail costs low. With lower retail costs there is of course an added risk of inter panel variance, which may lead to some quality control issues in some models.
UH-IPS and H2-IPS
UH-IPS and H2-IPS -
These are new names which some manufacturers seem to be touting a little. It has
been 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. 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.
Above: Close up macro photo of UH-IPS / H2-IPS structure from HP ZR30W screen.
Image courtesy of Zibri. Click for original source
Another new term being used by some manufacturers with the launch of their new IPS screens. 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. 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.
Performance IPS (p-IPS)
Above: NEC P241W
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. This is true at least for the 24" and 27" models, although the 30" model has not been released yet at the time of writing.
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.
HP LP2480zx 10-bit whitepaper