Why 100% SteamVR resolution does not match the native resolution of your VR headset!

when we go online and look at the specification of a vr headset such as the valve index for example we can see that the native resolution of that headset is clearly shown to be 1440 by 1600 pixels so why is it that when we place steamvr's resolution per ice slider on 100 we actually find the resolution to be higher than that native headset resolution let's take a look immersed robot the lenses in a vr headset allow us to focus clearly on a display that is only a few centimeters from our eyes but in order to do this they are required to bend that light at quite harsh angles causing varying degrees of distortion at various parts of the lenses if we were to render a rectangular image on a pc and send it directly to a vr headset at this native resolution then we would find that these distortions would manifest in warping of the rendered scene it wouldn't look like real life and the geometry of the virtual world would warp in distorting strange ways this type of distortion which affects these lenses is called pin cushion distortion in order to rectify this lens distortion vr software applies a correction algorithm to the rendered image before it's sent to the headset basically distorting the image in the opposite way this is called bowel distortion correction so now when the image is displayed in the headset the lenses continue distorting the way they always have but because the image was pre-distorted in the opposite way by the software the end result is a clear undistorted image where the geometry of the scene looks correct in the vr headset so what does this have to do with resolution well when the vr software applies this pre-distortion it effectively squashes the pixels together around the edge of the image while stretching out the central area the end result is a squashed and stretched image which doesn't quite fit the full area of the display there will be a black area around the edge of the image therefore the image needs to be expanded to fill the full display area once again this means that by applying this barrel distortion correction we are lowering the central resolution of the image by stretching it out in this manner if this was sent to the headset the image that we would see would actually be perceptibly lower than that of the native resolution of the headset in that central area so the answer to this is clear an increase in resolution also needs to be applied to the pre-distorted image in order to correct for the stretching out of the image in the central area and bring it back up to the native resolution of the headset therefore behind the scenes vr software generally renders the image at 1.4 times or 140 the resolution of the standard image if we take a look at the valve index specs again and multiply the horizontal per iron resolution which is 1440 pixels by 1.4 we get a corrected horizontal resolution of 2016 pixels if we do the same for the 1600 pixel vertical resolution we get 2240 pixels as we can see here this now matches perfectly to the standard 100 resolution slider in steamvr so that's why 100 steamvr resolution will always be 140 that of the native resolution of the headset this holds true for most vr headsets although i'm sure there are various headsets out there that use a different type of distortion algorithm and the corrected image has to apply a different resolution but for the most part 140 is the general rule thank you for watching and please leave a like if you found this video useful i'll see you next time please consider picking up my science fiction virtual reality focus novel the memory engine a light-hearted tong in cheek adventure through the metaverse available on amazon kindle paperback and as an audible audio book links in the description to this video [Music] you

Channel: Immersed Robot

Views: 47,456

Keywords: vr, oculus, quest, quest 2, virtual reality, rtx 3080, barrel distortion, steamvr, valve index, index, valve, resolution, resolution scaling, 100% resolution, native resolution, vr headset, pincushion distortion

Id: nyehrn9EKIY

Length: 3min 57sec (237 seconds)

Published: Mon Aug 02 2021

Reddit Comments

[u/ImmersedRobot]

TLDW:

I explain the specifics of barrel distortion correction, and why 100% SteamVR resolution scaling will usually be 140% that of the native resolution of your VR headset.

[u/OMGihateallofyou]

TIL Thank you!

[u/pharmacist10]

So if someone can figure out a way to create screens that do not result in distortion (I don't know if that's physically possible), does that means there would be significant rendering savings since you wouldn't have to correct for this distortion with higher resolution?

[u/MF_Kitten]

This means the outer edges will be way more densely detailed than the middle, while also being the least visible, which is why some kind of static foveated rendering would be very cool to see, though ideally it would just be fully foveated rendering. Maybe a combo.

[u/caltheon]

Wouldnt it make sense to have the outer parts of the render skip lines since it’s getting compressed to save on render

[u/SSJ3]

What I've always wondered is why everything is rendered in a traditional way and then barrel distorted for the lenses, rather than directly rendering with the distortion built in. I'm sure the math involved is pretty complicated, but in theory it would be the least wasteful way to do things.

Any ideas on why they don't do that? I'm wondering if it's simply because it's easier to do this way, or if it's something like wanting to maintain a whole lot of optimisations built into game engine rendering pipelines over the years. Like maybe it breaks MSAA or other features.

[u/Succulent_Orange]

If that's to compensate barrel then why does steam say "you should do 140% though" ?

[u/JewwyBewwy]

100% for me is lower than my headset’s resolution…wtf is happening