One of the most important characteristics of liquid-crystal displays (LCDs) is pixel response time. It is the time interval between the change of the signal in a particular cell and the change of the state of this cell. This parameter is also specified for classic cathode-ray tube displays and gas panels, but it is less crucial for them, as their response time is measured in microseconds. As for LCDs, the response time in them can reach tens of milliseconds, which may be noticeable for the human eye.
Despite some evident visual effects, such as the fuzziness of moving objects, response time cannot be more or less accurately estimated by the eye. One of the reasons is the inertia of the human eye itself (thanks to that, we don’t see the flicker of ordinary CRT displays, although every pixel of the screen glows only about 10% of the time).
In fact the problem of measuring response time looks simple at first sight: you could measure the time between the dispatch of the signal for cell state change and the actual change, tracking the pixel glow with the help of a photodiode. But it’s not that simple. The point is that you can’t pinpoint the time when signal is issued without meddling with the electronics of your display.
Another way: we could follow the vertical synchronization impulse and calculate at what time after it the data for our pixel are transferred, and adjust this time by the line synchronization impulse for the line containing that pixel… But such arithmetic only makes sense when you know exactly all time parameters of the scanning and assume that the display’s electronics doesn’t bring about any delays. The phenomena that can only be hypothesized upon, but not measured, don’t increase the reliability of the results. That’s why we put this method off, too.
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X-BitLabs.com
