How Much Game Performance Can We Perceive?
We measure game performance by the speed at which frames of video are fed to our eyes. The preferred unit of measure is frames per second (FPS).
There is a common misconception that 24 or 30 FPS is enough for perfectly smooth video, or that the human eye can only perceive up to 30 FPS. This stems from the movie and television industries. Movie theaters show film at 24 FPS, and that appears perfectly smooth, doesn't it? The fact is that our eyes are tricked into experiencing smooth video from 24 FPS source material because of motion blur. Film and video cameras capture moving objects by blurring their edges and the brain interprets this as smooth movement.
If you've ever had the chance to see a demonstration of movie playback at your local home theater electronics outlet, you might have noticed that movies seem a lot smoother than they do in theaters on some of the displays. This is because many modern televisions can modify the video, smoothing it out with anti-judder technology, and play it back at 120 Hz (or 120 FPS). Most folks easily notice the visual difference when movies are played back at 120 FPS with anti-judder enabled, which goes to show the human eye can perceive a lot more than 24 FPS. In fact, research suggests that human beings can perceive more than 200 FPS.
The point is that when it comes to PC gaming, more than 30 FPS is noticeable. In addition, the PC is an interactive device and the camera view often responds to user input from the mouse. The frame rate has to be quick enough to respond instantly to this user input. Otherwise, the user can feel the lag. This is especially noticeable in twitch games like first-person shooters that require precise aim.
Most PC monitors today cap out at 60 Hz, which means that the screen can refresh 60 times a second (there are a few 120 MHz monitors available for 3D use, but these are far from mainstream). Now, the question becomes: what if your PC is rendering more than 60 FPS? If your machine is fast enough to deliver 100 FPS to a 60 Hz monitor, what happens?
Unfortunately, more performance doesn't always equal better visuals. If your PC is sending out more frames than your monitor can display, what's likely going to happen is that the screen will refresh before the previous frame has finished drawing. This visual artifact is called tearing, and it's not pleasant. This is why vertical synchronization (v-sync) was developed.
Without going into details, v-sync limits your frame rate so that is doesn't exceed the monitor's, therefore eliminating tearing. When we benchmark games, we're usually looking for the performance cap, so we turn v-sync off, but for actual gameplay, you're probably better off enabling triple-buffered v-sync if your title supports the option.
We want to show you a visual difference between frame rates, but this turns out to be a lot more difficult than you'd think. Because of limitations in many popular browsers (Internet Explorer included), you probably see the following animated GIFs playing at the wrong frame rate right now. The result in Internet Explorer or Opera is particularly bad. Firefox and Safari do a better job, and will give you a passable idea of what 50 FPS versus 25 FPS looks like.