What is the real, physical, display resolution of my VR headset?
I have written a long article about the optical properties of (then-)current head-mounted displays, one about projection and distortion in wide-FoV HMDs, and another one about measuring the effective resolution of head-mounted displays, but in neither one of those have I looked into the actual display resolution, in terms of hard pixels, of those headsets. So it’s about time.
The short answer is, of course, that it depends on your model of headset. But if you happen to have an HTC Vive, then have a look at the graphs in Figures 1 and 2 (the other headsets behave in the same way, but the actual numbers differ). Those figures show display resolution, in pixels/°, along two lines (horizontal and vertical, respectively) going through the center of the right lens of my own Vive. The red, green, and blue curves show resolution for the red, green, and blue primary colors, respectively, determined this time not by my own measurements, but by analyzing the display calibration data that is measured for each individual headset at the factory and then stored in its firmware.
Figure 1: Resolution in pixels/° along a horizontal line through my Vive’s right lens center, for each of its 1080 horizontal pixels, for the three primary colors (red, green, and blue).
Figure 2: Resolution in pixels/° along a vertical line through my Vive’s right lens center, for each of its 1200 vertical pixels, for the three primary colors (red, green, and blue).
At this point you might be wondering why those graphs look so strange, but for that you’ll have to read the long answer. Before going into that, I want to throw out a single number: at the exact center of my Vive’s right lens (at pixel 492, 602), the resolution for the green color channel is 11.42 pixels/°, in both the horizontal and vertical directions. If you wanted to quote a single resolution number for a headset, that’s the one I would go with, because it’s what you get when you look at something directly ahead and far away. However, as Figures 1 and 2 clearly show, no single number can tell the whole story.
And now for the long answer. Buckle in, Trigonometry and Calculus ahead. Continue reading