Lag testing for 4K Displays

[BattleAxeVR]

Since Leo Bodnar's lag tester maxes out at 1080p60, I was wondering what's the best or standard way to measure input lag at higher refresh rates and 1440p or 4K.

Some recent 4K TV reviews have lag measurements that showed considerably less latency when fed 4K signals than 1080p signals, which makes sense due to less processing, but I wonder how they tested it.

Preferably something "free" (software) but I'd be willing to consider paid software- or hardware-based approaches.

Thanks!

[Sparky]

The high speed video method is a good starting point if you already have a camera capable of ~1k fps, but it's also incredibly tedious if you want any kind of accuracy. Basically you modify a mouse to light up a LED when you click, and count the number of video frames between the LED lighting up and the result on the monitor. More information on this method: viewtopic.php?f=10&t=3481

As a second option, It's not too hard to build a latency test device, this simulates a mouse input, then measures the delay to a change in brightness. This is my preferred method(because it is an absolute latency measurement, and you can get many samples with little effort), but it costs about ~$50 in parts(assuming you don't already have any electronics prototyping supplies):
My implementation: viewtopic.php?f=10&t=3005&start=50#p22634
flood's implementation: viewtopic.php?f=10&t=1381&start=310#p23272

A third option is to compare two monitors displaying the same output(a timer) with a still camera. Search for "SMTT" for more information.

[BattleAxeVR]

Thanks!