[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.

Measuring Response Time

Measuring response time is very simple, and consists merely of videoing the screen and the controller at the same time with a video camera that records at 60 fps, and then playing this back and counting the frames between button press and the screen response.

The camera I use is a Canon Powershot SD800IS, a relatively cheap camera. You need a camera that supports 60 fps (frames per second) recording. This may be listed as "Sports Mode", or "Fast Frame Rate".

I believe all the current line of Canon Powershot SD cameras have this feature. This is a very popular brand of camera, so it is highly likely that someone on your team will own one.

Set the camera to movie mode, change to to the appropriate mode for 60fps (press the "func" button on the Canon SD and select "Fast Frame Rate").

Then set it up to point at the television. You don't need to get the whole screen in shot, just enough so you can see the game actions that will result from your button presses. Make sure that the controller is roughly in focus and hold it angled so that the button presses can clearly be seen.