Ok, you’ve probably seen this already, but let’s try to understand why our vision system creates such a weird image distortion effect. Look at the .gif image below here. Focus on the white cross and keep your eyes on that during the animation. Why does your peripheral vision see? Why normal faces become weird distorted aliens? 😀
Here’s the trick: our brain blends images together if we scroll through them quickly enough. In cinema and animation, our eyes (and brain) start blending images if the frame rate is higher than 16 frames per second.
Instead of seeing flashing separated images, our mind is able to create a more or less continuous motion between each frame and the other. That’s why, for both physical film and digital cinema systems, modern theatrical films run at 24 frames per second (even 48 in the case of Maxivision). The typical example of this phenomenon is given by the Zoetrope, that produces the illusion of motion from a rapid succession of static pictures.
The phenomenon that is responsible for this is the Phi phenomenon, defined by Wikipedia as “the optical illusion of perceiving continuous motion between separate objects viewed rapidly in succession“. Together with the Beta movement, these two perceptual illusions represent a plausible theory to explain motion perception. In more general terms, we are talking about Persistence of vision. Again with the cinema example, movies are rapid sequences of discrete images, but persistence of vision smoothes out movement, making transitions subtle and comprehensive.