To be honest, it may simply be a bunch of new marketing on fairly old technology.
Unfortunately, there's no clear industry standard on how to measure response time. Previously, the way to measure it was to do a black-to-white-to-black response time (hence Tr + Tf which stood for time-to-rise plus time-to-fall). However, as was noticed later on, this was actually the lowest response time for LCDs, using conventional technology -- response times between grayscales were much longer.
Enter overdrive (or as ViewSonic calls it for marketing purposes, ClearMotiv, which encompasses overdrive and other technologies; Mitsubishi calls it Feedforward Driving), which speeds up the grayscale response times. If you're going from one-quarter brightness to three-quarter brightness, you just simply set the voltage as if you were going for full brightness, until the LCD reaches three-quarter brightness, at which point you set the voltage back to what's appropriate for three-quarter brightness. Previous technology was simply to set the voltage to three-quarter brightness from the start, and wait for the LCD to reach equilibrium with that voltage.
So now the fun part is that grayscale response times are faster than black-white-black response times -- hence it's become in vogue for companies that use overdrive to advertise gray-to-gray response times. There's another problem however: this is gray-to-gray, not gray-to-gray-to-gray. In short, they've magically cut the response time in half just by redefining how response time is measured, that is, only in one direction, rather than the sum of one direction and back. A response time of 5 ms under this new measurement method really means a response time of 10 ms under the old method. Unfortunately, it sounds better from a marketing point of view, so it's the method that we're stuck with now.
In recent years, of course, there's been gradual improvements in how this technology is accomplished. But it's an evolutionary, not a revolutionary, change. So the announcement is not as if they've uncovered some miracle breakthrough -- but simply that their marketing department feels the legal department feels the engineering department can justify the claim.
You can see documentation about this here:
Chi Mei (basic description of overdrive without the marketing):
http://www.cmo.com.tw/cmo/english/technology/technology.jsp?flag=20030304111549
Mitsubishi (note this came out in 2001; I think they were the earliest to research this concept, and this is their white paper on it):
http://www.mitsubishielectric.co.jp/service/tft_tech/new/img/sid_2001_29_03.pdf
Viewsonic (this is regarding the 4 ms panel specifically):
http://www.fastresponsetime.com/en/whitepaper.pdf
Obviously Viewsonic has a bigger marketing department because they were the ones to use www.fastresponsetime.com to promote their product (instead of the regular company website). But a couple of quick things I noticed while reading through their paper on it:
* Once again, marketing rears its ugly head -- even more interesting because this is supposed to be a white paper (compare the tone between Mitsubishi's and Viewsonic's). Viewsonic calls other overdrive technology "entry-level" without giving any details as to how its own technology is supposedly more advanced. Actually, I'm guessing that it may be by gradually ramping down the overdrive voltage as the LCD reaches the desired level, to prevent overshoot (that's from another diagram on the website). They don't say anything about that though, nor about how their overdrive is better. As an aside, this way of claiming to be better than everyone else when everyone already has more or less the same thing reminds me of how Formac offers a "zero dead pixel guarantee" for an extra $99 and claims that it's "a policy none of our competitors dares to offer" -- but upon reading the fine print, you find that it only covers if you have three or more dark whole pixels; many companies that work on a subpixel basis, such as Amptron (my company), HP, and Viewsonic, will replace a monitor if it has a single whole pixel defect of any type, and that comes for free (is part of the standard warranty). Be wary of people claiming to have some exclusive cool technology that no one else has.
* Looking at their graphs, I can't help but think something's wrong. Compare the graphs they give with the graphs given by Chi Mei and Mitsubishi. Notice the overall similarity with the latter two: going from any initial value to 0 tends to be very quick, while going from a high value to another high value tends to be the slowest, with the overall trend being that going to any higher value from any initial value tends to be slower than going to a low value from any initial value. This is from the pixel states for without overdrive. For Viewsonic's graphs, they reversed the scales (notice how both Chi Mei and Mitsubishi have 0's at the lower corner, while Viewsonic has 255 at the lower corner). But not only that, according to them, if it's labelled correctly, going from an initial value of 0 to any other value gives the fastest response time (before overdrive), while going from a high initial value to any other value tends to have the highest response times. This is completely at odds with the other graphs. The change is even more striking if you look at the graphs with overdrive. For Viewsonic, the lowest response time is initial value of 0 to any other value. For the other two, however, it's going from any initial value to 0. And no, this isn't simply due to reversing the 0 and 255 either -- if you reverse the 0 and 255 for Viewsonic, you end up with this low row on the bottom left, not the bottom right. The only reason I can think of as to why it's like this is if Viewsonic flipped the graph front-to-back. The only way that makes sense though is if the initial values are defined on the right bottom side, and the final values are defined on the bottom left side (reverse of what's shown). Regardless, the advantages of doing that is pretty apparent. The graph without overdrive has the high values in the front, which makes it look bigger; simultaneously, the graph with overdrive ends up having the back row on the left (next to the "5" which everyone sees first) all at their low values, rather than gradually increasing values (i.e. Chi Mei), which for Viewsonic are "hidden" at the lower left part instead. But unless they're using some really different technology, something doesn't look right.
* Where is that 4 ms figure from? If you look at the graph, the values vary greatly; anywhere from about 1 ms for 0 to 15, to a full 5 ms for a variety of values. While this is no doubt pretty quick, I can't see where they get that 4 ms figure from, other than a convenient marketing measurement (i.e. 12 ms then 8 ms and now 4 ms).
The fun part about this is that a monitor's control circuitry has a much bigger impact on the response time than the LCD panel technology itself (all this talk of overdriving is achieved via the circuit boards, not via the panel). However, the panel is the majority of an LCD monitor's cost. This means that in the future, it may well be possible to simply sell conversion kits (or better yet, software programs) to change your 25 ms monitor to an 8 ms monitor. Currently though it's much more profitable to claim that they've achieved some major breakthroughs to sell at a higher price, so no such kits or programs are yet available as a separate product.
Chuck Hsiao
Amptron
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