Input Lag Testing

It seems to be a common misconception across various internet forums that IPS displays have too much input lag to effectively game with. We have never believed this at PC Perspective, as we all game on IPS displays on our personal and test machines, and we set out to set the record straight, as well as compare the input lag of these Korean 1440p displays versus other conventional high resolution displays.

So you may be yourself asking "What is display lag?" and "Why is it important?" right now, and those are valid questions. Display lag is a relatively new thing in the computer display world. This input lag, as it is also known, was introduced in newer display technologies including LCD and Plasma.

This is due to the fact that displays such as LCDs have what we call a native resolution, or a certain number of pixels one each panel. In order to run resolutions that aren't of the native size, these monitors have to include things like scalers to appropriately size the input to fit the display. That, along with video processing including things like HDCP copy protection, add latency from the moment that the monitor receives the input to when it is actually displayed. It is important to note that the introduction of scalers and video processors does not necessarily mean that a display will have a lot of lag, but when they are implemented poorly, it can be disastrous.

In order to test for this lag, our setup included various high resolution displays, a DSLR camera, and believe it or not, a 17" CRT.

The idea behind this testing is that since CRTs have close to no input lag, by mirroring the output of a computer to both displays and displaying a millisecond counter on both, a camera with a high shutter speed (such as a dslr) will be able to capture any given moment in time. When we then analyse this picture, we can see the difference of the timers, which gives us the inherent input lag of the LCD.

Up first is a display which has been touted for years as a very low latency monitor, the Dell UltraSharp 3007WFP. This monitor only has a Dual-Link DVI connection, meaning that there is no scaler chip included, so latency should be low.

Here we can see an example of our testing, using the UltraSharp 3007WFP. By taking the difference between the readouts of both versions of the timer, we can see that the discrepency between the two is about 31ms, which equals to about 2 frames of movement at 60Hz.

In our testing of the 3007, we found the latency to be consistently around 32ms, which is pretty impressive.

(Editor: We have read that in some cases the graphics card can introduce a delay when mirroring outputs.  While this may be true, rather than directly measure the displays against the CRT, we are using the CRT latency testing to compare the LCDs to one another, against the "known good" Dell 3007WFP.)


Now let's take a look at the Dell UltraSharp 3008. On this model, Dell decided to include every input under the Sun (including things like S-Video and Composite video). All of these connectivity options certainly are nice, however it means that there is an input scaler, and a lot of video processing on this monitor, which may introduce a lot of lag. Let's take a look.

In this shot, and in all of our testing, we found the latency to be conistently around 45ms. While an extra 15ms may not seen like a lot, it is actually about another frame of lag when you figure in the refresh rate of monitors being 60Hz. It all depends on the person, but one extra frame in your way when you are trying to react in a FPS very well may end up being your demise.


Now let's take a look at the Achieva Shimian. Like the Dell 3007, this only has a single Dual-Link input, and we were expecting similar performance.

By taking a look at our images from the Shimian, we can see that our hypothesis was validated. Latency of this monitor is about 32ms, 2 frames at 60Hz refresh rate. Seeing as the 3007 is a highly regarded monitor in terms of it's low display latency, this is high praise for such a low cost product.

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