How to accurately measure input lag in video games

[qubit]

It's all in the camera and your trigger finger!

[How do you measure response time in games? Neversoft co-founder Mick West follows up a previous article on responsiveness with a cunning 'how-to' about using a digital camera to track responsiveness - benchmarking games from GTA through Heavenly Sword along the way.]

In this article I suggest that the specifications of a video game should always include a measure called "response time" (also called "lag", "controller lag", or "input latency").

Response time is defined as the time between the player using the controller, and the results appearing on the screen.

Example: Pressing the trigger button on the controller fires a gun on the screen. Video game response time can be measured with a cheap digital camera, and I explain how.
The Problem

The "feel" of a game is in large part described in terms of how "responsive" it is. Very often a game will be described as "laggy" or "sluggish", and by contrast other games will be "tight" or "fast".

I have previously described the technical reasons behind games lacking responsiveness, but I offered no way of measuring the response time, and so the developers have to rely on their own assumptions about the way they read the controller and present the results, and combine that with the subjective assessments of the test department.

Having an accurate way of measuring response time allows the developer to both verify their own assumptions (hence detecting bugs that are adding to the response time), and to provide an objective reference to the claims of the testers regarding the "tightness" of the game.

Perceptions of changes in small variables like response time can vary by individual, and being able to measure it objectively will allow you to see if it has actually changed, and by how much.

Game developers also have to make the decision of whether to go with 60fps or 30fps. 60fps will generally have half the response time of 30fps, which can be a deciding factor (along with the smoother motion, which is visually more appealing on fast moving games). However for some games there are other factors that influence the response time.

Having an accurate way of measuring the response time allows the developer to more accurately and objectively make a decision on if 60fps is necessary, or if they simply need to tighten up their 30fps game.

Read the rest at Gamasutra

 

[Nordic]

Seems like it would be a bit harder to do with a mouse and keyboard.

 

[Delta6326]

I don't see why devs go with 30fps I try to keep all of my games at 45fps minimum. I can always tell a game at 30fps with lag.

 

[m1dg3t]

I don't see why devs go with 30fps I try to keep all of my games at 45fps minimum. I can always tell a game at 30fps with lag.

IIRC it's what each human eye "sees" from a 60Hz display....

 

[Nordic]

I don't see why devs go with 30fps I try to keep all of my games at 45fps minimum. I can always tell a game at 30fps with lag.

I like 50 myself. Back when I was running my 9800gt I would settle for 25fps though. Anything less than 25fps is unplayable.

 

[Solaris17]

i still find it depends. i mean i remember we used to have threads arguing about which was playable but really it all depends on the person. someone thats a casual gamer usually wont have the response time of an avid player so 30/60 FPS is worlds of diffirent between them. imo as long as its above 30 i honestly dont care high FPS is great and I try to get it their but my big issue is steady. going from 340 to 130 fps is still "fluid motion" to the human eye but when your playing a FPS or watching a spell on an RPG an FPS flux like that can really screw stuff up and you can definitely feel it.

 

[phanbuey]

lol this is from the other thread... human eye can see well above 100 FPS - it is a huge myth that we can only see at 30 and no more.


http://whisper.ausgamers.com/wiki/index.php/How_many_FPS_human_eye_can_see

 

[BazookaJoe]

i still find it depends. i mean i remember we used to have threads arguing about which was playable but really it all depends on the person. someone thats a casual gamer usually wont have the response time of an avid player so 30/60 FPS is worlds of diffirent between them. imo as long as its above 30 i honestly dont care high FPS is great and I try to get it their but my big issue is steady. going from 340 to 130 fps is still "fluid motion" to the human eye but when your playing a FPS or watching a spell on an RPG an FPS flux like that can really screw stuff up and you can definitely feel it.

Fantastic reply.

Fact is although some people really are comfortable with 30fps , others REALLY can tell the difference just by looking, and anything less than 60fps can really feel unpleasant to them. Its sort of an itchy scratchy behind the eyes feeling, and it can completely ruin a product for those who can tell the difference.

But far beyond either of these is the matter of consistency. The greatest enemy to anything is FLUCTUATIONS in frame rate - your brain will begin to get into a groove with just about any frame rate over time, but when it starts fluctuating that is the worst of the worst.

 

[1nf3rn0x]

I honestly find some titles to be smooth even when under 60fps e.g BF3 and the original Crysis, yet games like COD seem very laggy even when dipping <60 for me. It depends on the game, and what you view as playable.

 

[BazookaJoe]

lol this is from the other thread... human eye can see well above 100 FPS - it is a huge myth that we can only see at 30 and no more.


http://whisper.ausgamers.com/wiki/index.php/How_many_FPS_human_eye_can_see

100% agree - the myth actually originated from a MISUNDERSTANDING in technical specs back in the early days of display tech where the phosphor coatings in the screens actually took so long to respond to a change in electron stimulation that it was considered not possible to visually alter the image on a screen faster than 30 FPS as the phosphor simply could not react fast enough.

Those responsible for standards then stuck with the rule of thumb that there was no point running faster than 30fps in video images as an increase in speed would be imperceptible to the eye, due to the technologies limitations, and over time the science of WHY was forgotten, and only the part about only perceiving 30Fps was remembered.

As our eyes are in fact analog devices we don't see in FPS at all - rather in "Change Over Time" - a funny fact if you lock a human eye exactly in place so it cannot move at all, within seconds the entire field of view fades to black, we rely on movement and change in our vision to see at all, and many studies have presented arguable evidence that even though we are not consciously able to react this fast in daily life, our subconscious can actually react to movement as fast as, if not faster than, 1.8 milliseconds - partially proven in a test where harmless but visible particles of sawdust where fired at the eye from sharp angles off to the side so that they only became visible less than a centimeter away from the eye, and many subjects where still able to blink and deflect the sawdust particle before it hit the eye (roughly 1.9 ms response time)

So next time some idiot tries to tell you that 2ms screens are pointless you can tell him to go pick the sawdust out of his eye...

(EDIT : Sawdust / cotton fluff - whatever some sort of small visible - non damaging thing I cant remember exactly what)