Measuring the Effective Resolution of Head-mounted Displays

Why does everything in my VR headset look so pixelated? It’s supposed to be using a 2160×1200 screen, but my 1080p desktop monitor looks so much sharper!

This is yet another fundamental question about VR that pops up over and over again, and like the others I have addressed previously, it leads to interesting deeper observations. So, why do current-generation head-mounted displays appear so low-resolution?

Here’s the short answer: In VR headsets, the screen is blown up to cover a much larger area of the user’s field of vision than in desktop settings. What counts is not the total number of pixels, and especially not the display’s resolution in pixels per inch, but the resolution of the projected virtual image in pixels per degree, as measured from the viewer’s eyes. A 20″ desktop screen, when viewed from a typical distance of 30″, covers 37° of the viewer’s field of vision, diagonally. The screen (or screens) inside a modern VR headset cover a much larger area. For example, I measured the per-eye field of view of the HTC Vive as around 110°x113° under ideal conditions, or around 130° diagonally (it’s complicated), or three and a half times as much as that of the 20″ desktop monitor. Because a smaller number of pixels (1080×1200 per eye) is spread out over a much larger area, each pixel appears much bigger to the viewer.

Now for the long answer.

Continue reading