A couple of drawbacks
Even if it looks great on the paper, the overdrive still has a couple of problems. Some clues lead us to ask ourselves if they are not overselling the product.
1rst doubt: the real gain
For example if we only trust measures published by ViewSonic (probably obtained by the panel manufacturer, AU Optronics), the rise and fall times after the crystals’ overtension are:
Bars only represents rise or fall timeIt seems very efficient. Some of the rise times have been decreased from 80 ms approximately to 20 ms. But, if you look carefully, it is almost a bit too efficient. Even the white-black-white time is decreased by a couple of tenth of seconds despite the fact that this voltage was already set to the maximum. Therefore, it shouldn’t be possible to amplify it and logically performances could not be improved. ViewSonic justifies this increase and explains that this ClearMotiv technology is an improved version of the Overdrive. We really want to believe them but it does seem quite surprising.
2nd doubt : AU confirms our feelingDuring the CeBit 2005, we met one of the AU Optronics panel specialists. He confirmed to us what we have been telling you for years, TN 16 ms, 12 ms and 8 ms panels are absolutely identical. The only difference is in some of the electronics and the overdrive on top. He was not surprised to hear that we haven’t noticed any improvements in practice from one generation to the other. He explained to us that this overdrive was far from regarding all grey color changes. Only some of them, but he didn’t give a figure, are concerned. The final RT between greys would be the best one found among all of those set in place.
Compared to the previous ViewSonic, this graph, published this time by Eizo (who doesn’t manufacture any panel either) seems a little more realistic and appears to meet AU Optronics remarks:
The improvement brought about here by the overdrive is obvious but unequal from one color to the other. Here, not all color transitions are necessarily accelerated. The one from white to grey especially remains more or less steady.
3rd doubt: what is the real influence of response time on the monitor reactivity?If we follow the theory, the monitor reactivity would be directly connected to the afterglow noticed.
It is interesting to notice that the manufacturers’ position has changed over time.
Initially, a few jokesters told us that it was related to the refreshing frequency, as with the CRT monitors. That explanation didn’t last long.
Then, the ISO response time was given as the explanation for the presence, or not, of blurred effect with motion.
Today, a few manufacturers say that the response time doesn’t mean anything anymore and that it is the grey level that is important. They base this argument on their own measurements, the same that we introduced to you under the shape of the 3D graphs. The problem is that the same manufacturers also admit the following table (also based on ViewSonic’s whitepaper):
According to these measurements (LG-Philips and Nec at least have published similar results) TN panels would be the least "gifted" for color changes between greys. According to this chart, the MVA would be the best, followed by IPS panels. Of course, when an IPS manufacturer speaks of these charts, the order of the two first is reversed.
In fact, that doesn’t matter: in practice our eyes led us to an entirely different conclusion. Whatever the values obtained are, up to today no IPS or VA panel has ever been as reactive as a TN panel announced as 20ms or below. Whether it is a monitor with overdrive or not.
So two possibilities have to be considered:
1 – All measurements are fakes. It would be unfortunate if engineers designing panels aren’t able to correctly measure this response time.
2 – Measures are accurate. In this particular case, it means that the crystals’ response time factor would only be one factor among others for monitor reactivity.
Unfortunately we are unable to give you a lead on what could influence the panel reactivity except for the crystal reactivity. This is an announcement to all electronics enthusiasts, liquid crystals specialist, and panel manufacturers: please share your knowledge!
