This is one of those questions that comes up so often that I’ve decided to do a blog post about it.
People will often watch 360 videos, either monoscopic or stereoscopic, and be disappointed in the quality. Regardless of who created the content, people frequently seem surprised at the poor resolution — even when the video is 4K. They often (mistakenly) think it’s a limitation of the VR headset, which it’s not.
In fact, people will sometimes compare content created using a realtime game engine such as Unity (e.g. The Lab on HTC Vive or Dreamdeck on the Oculus Rift) to recorded 360 degree video, and wonder why the 360 video looks so much worse than the game engine content.
I’m going to try to give a simple explanation of where the problem is.
Let’s start with some math. Most VR headsets have a field of view of 100 degrees. That’s measured diagonally, same as with television sets. If you buy a 60 inch TV, that’s 60 inches measured diagonally (corner to corner). Same with VR headsets — they’re 100 degrees diagonal, with an approximately square aspect ratio for each eye, so you have approximately 72 degrees horizontal by 72 degrees vertical. In other words, one fifth of a full panorama (360 divided by 72). That’s an important number, so keep it in mind.
So let’s say you shoot a 360 stereoscopic video and render it out at 4K resolution. First of all, “4K” is not really 4K. Most people use “4K” to refer to UHD, which is actually 3840 pixels horizontally by 2160 pixels vertically. Assuming the image is stored in SBS format (Side By Side — left eye image in the left half of the screen, right eye image in the right half) then you’re only left with 1920 pixels horizontally per eye.
Now, you may be thinking “No problem — that’s still full HD resolution for each eye. Should be plenty!”.
However, here’s the thing – – those 1920 pixels are spread out over the full 360 degrees. Since (as described above) you can only see 1/5 of those 360 degrees at any given time, you’re getting 1920/5 or 384 pixels horizontally. It’s a bit better in the vertical direction — you’re getting 72 degrees out of 180, or about 1/2.5. so you’re seeing 864 pixels vertically.
A modern VR headset has way higher resolution than that. The Gear VR gives you 1280 by 1440 pixels per eye, vs 384 by 864, so the headset is capable of displaying nearly six times as many pixels as are actually in your video. To put it another way, each pixel in your video is stretched out to cover approximately six pixels on the screen. It’ll either be very pixelated or really blurry, depending on how the video was processed.
And of course, if you’re streaming, you also have to compress the video down to a bitrate that can be sent over the internet. That compression further reduces the visual quality.
So 4K is just barely adequate. For current VR headsets, 8K is much better. However, if you’re using mobile VR, then you’re limited by the available codecs (which may not support 8K, since it exceeds the resolution of the phone’s screen).
All of this does not mean you shouldn’t keep making 360 videos! Just be aware of the limitations of the medium, use the highest resolution your target platform supports, and manage your clients’ expectations accordingly.