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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.

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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.

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Remember this diagram? This is full persistence – the pixels remain lit throughout the frame.

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  • WormSlayer

    My brain hurts! Still I’m excited that guys like him are excited :D

  • Patrick Hogenboom

    Thanks a bundle for transcribing the whole thing :)

  • shole

    If you want to view the two videos in the presentation and don’t have ms powerpoint, you can rename the .pptx file to .zip and the files are in there as .wmv under \ppt\media\

    • Michael Abrash

      Shole,

      Thank you very much for posting this!

      –Michael

  • Andrés

    Thanks so much for transcribing this!

  • Andreas Aronsson

    I thought I would not get to read/hear the actual talk in some time :D Very interesting, somewhat alarming, but at the end uplifting and inspiring! Thanks for this! Also, you could if you wanted to rename the .pptx to .zip and extract the videos (media folder) and upload them unlisted to Youtube and embed them on this page :) Just a thought!

  • Andreas Aronsson

    Ah, in the time it took me to read this (left the article half-read over night) shole already pointed this out :x oops.

  • Esse

    “That means that if you fixate on something while you turn your head, your eyes remain fixed with respect to the real world, but move very quickly relative to the display”

    Hum, no. If your eyes are fixed (in the head referential), they are fixed in the display referential. Because the display & the head are fixed one to the other.

    This is over complicating the subject. Only matters the head movement. Not the eyes movements.

    • Ben

      I think that, in this context, “fixate on something” means a visual fixation on an object in the external world rather than having the eyes be “fixed” relative to the head. If the head is turning while you fixate an external object, the eyes must counter-rotate in order to maintain a stable fixation (eg: via the VOR). Since the VR display is attached to your head frame, this means that your eyes are rotating relative to the display, and that’s the source of the large relative motion that causes issues.

      • Michael Abrash

        Ben,

        You’re correct – that’s what I meant. If you look at a key on the keyboard and keep doing that while you turn your head, you can easily get your eyes moving at several hundred degrees per second relative to the display.

        –Michael

  • Esse

    “The human perceptual system has evolved to be very effective at detecting such anomalies, because anomalies might be thinking about eating you, or might be tasty.”

    It is not some specific “anomalies detection system”, rather that the human brain has in-depth “routines” to analyse the space & movement, and when you broke the rules the routines fail.

    Like when you are sick in a car.

    So I guess the reaction will not be fear or drooling, more puking.

  • Ben Humberston

    Thanks for the transcript for those of us who couldn’t be there!

  • Mattso

    Yeah, just echoing the sentiments above that having it all transcribed meant I actually got to digest it really quickly. Many thanks!

    Very informative stuff – and here was me thinking it was gonna be easy. :)