For Science!
6 Frame Rate Facts You Didn't Know

CJ Miozzi | 12 Nov 2014 16:30
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Gamers will vociferously defend the superiority of 60 frames per second over 30. Moviegoers will lament the loss of that cinematic feel when watching The Hobbit at 48 FPS rather than the traditional 24.

With frame rate issues once again in the headlines, I thought this an opportune time to revisit the great frame rate debate in video games and cinema. But we'll take a different angle - rather than try to convince you that something is better or worse, here are six facts about frame rates that you may not have known. They may just change your opinion - or further entrench you.

1. The FPS "limits" of the human eye

First off, a question people often ask is: how many frames per second is enough? At what point can we no longer perceive any difference in FPS? The answer, unfortunately, isn't black and white.

In their book, Restoration of Motion Picture Film, authors Paul Read and Mark-Paul Meyer write, "The human eye and its data reception and transmission system can form, transmit and analyse 10-12 images per second."

Now hold on - does that mean that we cap out at 12 FPS? No. The key word in that quote was "analyse" (British spelling). The mind can interpret up to a dozen separate images shown sequentially. Beyond that, we begin to perceive a continuous animation.

"The vision centre in the brain retains each individual image for one-fifteenth of a second. If [it] receives another image during this fifteenth of a second, the sight mechanisms will create the sensation of visual continuity."

So 10-12 FPS is effectively what distinguishes animation from a slideshow, forming our lower limit. But what about an upper limit?

"In laboratory testing, it has been found that the human sense of sight can distinguish up to 48 flashes of light per second, the switching from light to dark not being detected when they take place at higher rates of speed."

What this means is that, above 48 FPS, the effect we call "flicker" should no longer be noticeable. That said, vision is a complex system. In very bright rooms, flicker can be noticeable at higher frame rates. Larger displays (or small displays that you get very close to) produce more noticeable flicker, because our peripheral vision is most sensitive to this effect. The sweet spot where flicker becomes unnoticeable to most people under most conditions is 70-90 FPS.

Why is flicker important to this discussion? More on that later, but sadly, this still isn't an upper limit, just another lower limit. It turns out that, when dealing with still frames that do not have motion blur - which we'll get to as well - more frames per second will always result in a smoother visual. In fact, the faster the on-screen movement, the more we are able to distinguish "choppiness," and thus the higher the FPS we need to achieve a smooth image.

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