In gaming, input lag is defined as the delay between the when a user does something with an input device and when that action is reflected on the monitor.

The definition is straightforward, but the reality of input lag is much more subtle than may readily be apparent. There are many smaller latencies that contribute to the overall whole of input lag and understanding the full situation may prove beneficial to gamers everywhere.

The first subtlety is that there will always be input lag. Input lag is an unavoidable reality that can only be minimized and never eliminated. It will always take some amount of time for input data to get to the software and it will always take some amount of time for the software to use that data to display a frame of animation on the monitor. Keeping this total time as low as possible is a key mission of hardcore twitch gamers out there.

This article will step through all the different contributors to input lag, and we'll give some general estimates on the impact of each different contributor. Exact numbers will vary widely with different hardware and software combinations. But knowing where to focus when optimizing for input latency should help those who are interested.

After drilling down into the causes of input latency, we will provide a few examples of different hardware and settings in our lab. The extra twist is that we will be evaluating actual input latency using a high speed camera to count frames between input activation and monitor response. We'll be looking at three different games with multiple settings on both CRT and LCD monitors.

Reflexes and Input Generation
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  • RubberJohnny - Friday, July 17, 2009 - link

    OT - I used to be a diehard CRT ONLY user then i realised there is NO ghosting on modern LCD monitors...you may have seen smearing on LCD tvs but thats caused but the scaler resizing SD material to fit the panels native res.
    On monitors there is no scaling = no ghosting.
    Got a 24inch samsung 6 months ago and wish i'd done so earlier, crisper, larger image and widescreen being the main reasons i'll NEVER use a crt again.
    Reply
  • DerekWilson - Friday, July 17, 2009 - link

    I agree that with modern LCD panels ghosting is not as large an issue and color (depending on backlight) and contrast (depending on panel) are much better these days as well.

    Refresh rate is the only real outstanding issue these days (imo). And the only 120Hz display I saw was a bit over saturated / over bright and not high enough contrast.
    Reply
  • jkostans - Saturday, July 18, 2009 - link

    I have yet to see an LCD without ghosting, it may be minor but it's still annoying. And even the 120Hz LCDs supposedly still have measurable input lag regardless of the non-existent ghosting. LCDs are still a downgrade as far as I'm concerned. Reply
  • DerekWilson - Sunday, July 19, 2009 - link

    Well you can actually see how much (or little) ghosting there would be in our high speed footage... even the advertised latencies on the 3007WFP are pretty bad compared to most panels these days (especially TN panels). Despite that there were only a few cases where we could see ghosting take a whole frame (and it never seemed to take more than a whole frame).

    We should test more panels with high speed cameras and see what happens...
    Reply
  • Freeseus - Thursday, July 16, 2009 - link

    I feel like there is a HUGE section of delay missing from this article. Perhaps it was chosen specifically not to be included because rigorous testing/comparison would have to be performed in order to show any sort of suggested "average" numbers. Either way, I feel it should have been addressed... even if it were just at the end of the article.

    I'm referring to the added delay of wireless mice.

    Aside from the added delay of transmitting all the mouse action to the receiver, the biggest issue is the inconsistencies of mouse performance and precision. I'm sure there's a direct correlation between this and the battery. I'm referring specifically to the amount of battery used up in order for the mouse to broadcast continuously at extremely high intervals to insure precise movement. But obviously this includes any issue where the battery needs to be recharged as well. And on top of that, the mouse seems to be non-responsive occasionally during use. Completely unacceptable in a work or 'twitch gaming' environment.

    Anyhow, it would have been nice to see this addressed because many people make the argument that wireless mice are better. And when it comes to FPS gaming or even work, I can't think of a reason not to have a wired mouse. Do I really need to have that accuracy all the time. Yes.
    Reply
  • DerekWilson - Thursday, July 16, 2009 - link

    I agree that the current state of wireless mice is generally pretty poor ... though I've never used a wireless mouse targeted at gaming (gaming mice were the first optical mice I was able to use without mousing too quickly for the sensor even during desktop use).

    Testing wireless mice is definitely something worth looking into.
    Reply
  • Vidmar - Friday, July 17, 2009 - link

    What about PS/2 mice? Are they better or worse than USB? Reply
  • DerekWilson - Friday, July 17, 2009 - link

    PS/2 mice are slower ... iirc they come in at about 100Hz (10ms). Reply
  • Vidmar - Monday, July 20, 2009 - link

    Really?? My old PS/2 MS Wheel Optical Mouse v1.1 is currently running at 200Mhz. IE: 200 reports/second. I've never felt like it doesn't keep up in any game. Reply
  • lopri - Thursday, July 16, 2009 - link

    I'm loving this article and chewing threw every page right now. Just wanted to say thank you for such in-depth analysis as is rarely found elsewhere. Reply

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