Now, what happens if your eyes are moving relative to the display, for example if you’re tracking a moving virtual object from left to right?
The color components of a given pixel will each line up differently with the eyes, as you can see here, and color fringes will appear.
Remember, these diagrams are relative to the position and orientation of the eyes, not the real world.
There’s actually another important implication of this diagram, which I’ll talk about shortly.
Here’s how the color fringing would look – color fringes appear at the left and right sides of the image, due to the movement of the eyes relative to the display between the times red, green, and blue are shown.
You might ask how visible the fringes can really be when a whole frame takes only 16.6 ms.
Well, if you turn your head at a leisurely speed, that’s about 100 degrees/second, believe it or not; you can easily turn at several hundred degrees/second.
At 120 degrees/second, 1 frame is 2 degrees.
That doesn’t sound like a lot, but two degrees can easily be dozens of pixels and that’s very noticeable.
So VR displays need to illuminate all three color components simultaneously, or at least nearly so.
Now we that we understand a bit about the temporal sampling done by displays, we come to persistence – that is, how long each pixel remains lit during a frame.
If you understand why color fringing occurs, you already know everything you need to understand why persistence itself is a problem.
Persistence ranges between 0 ms and an entire frame time (or more!) for various display types.
Remember this diagram? This is full persistence – the pixels remain lit throughout the frame.