Does Overdrive really cause input lag?

[KeeperFiM]

I have a 2010 iMac 21.5 in running Windows 7 via Boot Camp. I have the legacy 13.1 Catalyst drivers installed for the Mobility Radeon HD 4670 256mb. In the CCC enabling LCD Overdrive seems to greatly reduce ghosting and improve smoothness, and I haven't been able to feel any increase in input lag (in games or otherwise). I am really sensitive to input lag so I am surprised that I did not notice any. Does it really increase input lag so much?

Oh, and I turned overdrive to the maximum value (200) by the way.

 

[Anarchist420]

If the GPU is doing it then it shouldn't cause any input lag.

 

[KeeperFiM]

If the GPU is doing it then it shouldn't cause any input lag.

well that makes sense, thanks.

 

[BrightCandle]

I have absolutely no idea how the overdrive works in AMDs drivers, I am not confident that it wont introduce input latency. But presumably it must work in roughly the following way:

1) It needs to store the previous image, the one that the monitor is displaying (ignore monitor lag).
2) The current screen must be compared to the previous one and a series of adjusted colours put in to cause the overdrive effect.
3) The adjusted image is sent out.

However you measure the work of (1) and (2) must slow down the image somewhat. Its highly likely its a simple calculation, it requires a pixel by pixel comparison to the images and presumably a relatively simple calculation on what the colour should be to cause an overdrive like effect. So I think its likely it does cause some amount of input latency, but whether its 1ms or 16ms I really don't know.

 

[Ben90]

I'm confused with the terminology here. A GPU has no possible way to overdrive a monitor unless it is running at completely unrealistic refresh rates (in the thousands). Otherwise you are just distorting the image for pretty much no gain.

Sounds to me like the driver is just communicating to the monitor to have it do overdrive. Here, even though there are technically more calculations, it actually reduces input lag because the pixels change state faster. All the overhead is built into the display controller, most LCDs use overdrive by default.