^Wouldn't G2G be MORE optimistic than ISO black-white-black? After all, it's a smaller transition and therefore faster, right?
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I more meant that quoting a G2G response time gives a better overall view of the panels performance than an ISO response time. Where overdrive is used, and therefore a G2G figure given, the pixel transitions across the whole range tend (normally) to be quite regular, and certainly the overall performance shows a marked improvement compared with screens without overdrive.
For example a typical response time graph from back in the day of panels without overdrive, representing a fairly typical TN Film panel
The ISO response time would be represented at the far right hand edge where the fastest measurement is taken. This has not accounting for the fact that all the other transitions are much slower than this point, and the overall performance really varies a lot.
response times of other panel technologies were even worse, this is from a typical VA panel without overdrive. The ISO measurement is again the best case, and all G2G transitions are much slower, some massively so
So the ISO response time is fairly meaningless as it gives you no real indication of the panels performance in my opinion. Back then, a TN Film panel would have been rated with a 12ms or 16ms ISO response time commonly, and a VA panel with an ISO response time of ~16ms also. While that ISO measurement might have been similar, it wasn't a true reflection of the real life performance.
On another note, measuring a transition change from a full black > white transition is far less realistic in real life situations than changes between different grey shades and colours.
A panel with overdrive would have had a much flatter graph. for example the ViewSonic VP191B was one of the first VA panels to use overdrive:
(green line)
So the quoted 8ms G2G figure gives a more accurate view of the response time since the performance is fairly consistent across the whole range of transitions. 8ms is still the "best case" measurement admittedly, but since it uses overdrive you can at least assume that more of the common G2G changes have been sped up.
As i say, panels with overdrive commonly have a fairly similar response time across the whole range, whereas panels without have a real variety of response time measurements.