So What About Gray-to-Gray Latency?
What's the point of this Gray to Gray latency measurement? If you look at the ISO latency (0 -> 255 -> 0) of this panel, it's a 15 ms panel. That's clearly unacceptable from a marketing point of view, when TN+film panels offer 8 ms ISO. So another means of measuring was needed so that these new panels, which are genuinely superior to former ones, can take on a competitive aura in consumers' minds.
Gray to Gray latency is "defined" as the time it takes a pixel to change from one shade of gray to another - such as from 128 to 255. Clearly that's more representative than the ISO latency measurement, but it's still not enough since part of the problem remains hidden. Suppose it takes a panel 8 ms to go from 128 to 255. How long will it take to go from 255 to 128? That's not taken into account in the measurement.
To our way of thinking, latency must be measured on a complete cycle and not just a half cycle, since behavior can be radically different on the signal's rise and fall. Only a question of method, you say... Not really: any electronics engineer will tell you that response is calculated by taking the sum of the rising time and the fall time.
And in fact that's what we see when we do the testing ourselves. The panel does take an average 8 ms to go from 128 to 255, but it also takes 8 ms to return from 255 to 128 ms. So its latency is 16 ms. Of course, from a marketing point of view, 16 ms cannot be sold nowadays, so the specification is cut in half, keeping only the rising time and the result is a more sellable latency specification of 8 ms.
The bottom line is that due to manufacturers' miscommunication, the situation will become more and more complicated for purchasers. Until now, for latency, you already had to understand the technology and take the type of panel (MVA, TN, or IPS) into account. Now, you'll also have to deal with the differences between measurement methods used by manufacturers.
Or Else Read Tom's Hardware
Don't worry. As far as we're concerned, our method will not change. It still takes the entire range of possible latencies into account, including ISO at point 255 of the curve and Gray to Gray at point 128. This method still seems much more representative of what you'll really be aware of in terms of latency in your films and video games and there's no reason to change just because manufacturers change their minds in order to publish sexier figures.
The bottom line is that MVA/Overdrive shows that manufacturers are moving in the right direction and we feel that the VP191b is an excellent monitor from this point of view.