Understanding Pixel Density - Making sense of it

[DerekSpeare]

Greetings Friends of VR,

 

It's my opinion that a clearer relationship between "Pixel Density" and your VR device's resolution should be made, and it's my intention with this post to - hopefully - make it clearer so folks can use this setting to their advantage.

 

Right now DCS allows us to adjust the VR Pixel Density directly in the "VR Options" tab. It's set to 1.0 by default (IIRC). What does that number really represent? Great question! A Pixel Density (PD) of 1.0 is really a resolution value, and that value is the native screen resolution your VR device; with the CV1 and Vive it's 2160x1200 and with the DK2 it's 1920x1080. Therefore, when you set the PD to 1.0 you are simply running your VR application at the device's native resolution.

Ok, Derek, tell me what happens when the PD is set to 1.5? I will!

 

When you set the PD to 1.5 you "upscale" your device's resolution to a value of 1.5 times what it is natively. In the case of the CV1 it's 2160*1.5 x 1200*1.5, or 3240x1800. Make sense? It should...

 

So, then you can see what happens when you run the PD to 2.0. There you'd have a 2160*2 x 1200*2, or 4320x2400 resolution running. You can see another relationship emerging as well, and that's that the total number of pixels being rendered increases exponentially to the increase in PD.

 

Here are the total Pixels for popular values:

 

PD = 1.0 => 2160x1200 resolution = 2,592,000 pixels

PD = 1.5 => 3240x1800 resolution = 5,832,000 pixels

PD = 2.0 => 4320x2400 resolution = 10,368,000 pixels

PD = 2.5 => 5400x3000 resolution = 16,200,000 pixels

 

What I recommend personally to anyone is that they keep their PD value to whatever number gives that a solid 90 base simulation frame rate (or as close a possible). If you ramp it up too aggressively you run the risk of frame rate degradation to the degree that ATW cannot compensate and you get ghosting, judder and, worse, VR induced disorientation and discomfort.

 

(Note carefully that it's often the case where no computer will run DCS at a base simulation frame rate of 90fps. You're encouraged to reduce your settings the best you can in order to keep frames as high as possible)

 

We can also draw a parallel for those who want to determine if their PC will run DCS well with VR. Say "Misha Mignichnik" has a three screen setup and he wants to know if his PC will "run DCS in VR". He can easily run test flights in various locations, conditions and aircraft while running a framerate test on each one. If he has frame rates running at ~90 or more all the time then he knows with ease that he can - should - run DCS with VR; e.g.:

 

Misha runs three screes at 1920x1080 x 3 => 5760x1080 resolution = 6,220,800 pixels generated. If Misha can run that then he "should" have a good VR experience as his PC has enough power to do it.

 

I hope this helps folks understand the relationship between Pixel Density, Screen Resolution and expected pixels per frame more clearly.

 

NB: You can also see that if you're running a PD of 150 and generating a total of 5,832,000 pixels per frame cycle, then if you're getting 90fps you're generating a whopping 524,880,000 pixels per second! WOW!

[Gman109]

Does this mean you don't have to go into files and edit them with notepad any longer like this thread below in order to change your pixel density? I have a Vive en route, so I haven't tried it myself yet, but want to know beforehand if I should be going into files editing stuff or just using the "VR options" tab for PD as you said.

 

http://forums.eagle.ru/showthread.php?t=169141

[DerekSpeare]

P2S1 above:

Right now DCS allows us to adjust the VR Pixel Density directly in the "VR Options" tab.

 

It should be obvious what to do.

[AstroEma]

Actually Pixel Desnity adjustment in the VR Tab only works for the Rift, not the Vive.

 

To adjust pixel desnity on the Vive you need to edit the VRSetting file in the Steam folder.

[KLR Rico]

I did some testing last weekend to find that "Image quality vs frame rate" sweet spot.

 

I recorded a track, and then played it back at different pixel densities while recording performance information with MSI afterburner.

 

I found that I can maintain 90 FPS pretty well right up through a density setting of 1.6. The real limit is somewhere between 1.6 and 2.0, but that gap is bigger than it seems because the GPU load is exponential to the density setting. I'll probably test again to narrow down where the sweet spot is hiding in there, but there are probably lots of situations where I'd hit a GPU limit even at 1.6 (like dusk/dawn, in weather, etc).

 

It's also worth noting that there are points here where frame rate takes a hit regardless of the graphics settings, these were mainly the parts where I was diving in on targets and the simulation was CPU bottlenecked. It's also kind of strange that there are lag spikes that were only felt at 1.0 and 2.0, I'm not sure what caused those.

 

[whitav8]

What is also important to note is that during the downscaling back to Rift resolution, the resultant image is considerably antialiased already with more intermediate colors than the original had. I'm not sure what shader/hardware algorithm is being applied - and one wonders if that could be further optimized. All I know is that Pixel Density Override has made our first generation VR a much better experience than any AA algorithm could ever have made on the standard resolution.

[Brun]

I think the term 'pixel density' used in this context is really misleading. Pixel density is really a parameter of the screen, commonly expressed in pixels per inch or PPI on regular monitors. Pixels per degree would be more appropriate for VR, which by my reckoning is about 11 for current hardware.

 

Increasing the 'pixel density' is simply supersampling (exactly the same as nvidia's DSR etc) where the image is rendered at higher resolution before being downsampled. It's essentially just a very brute force way of rendering a higher quality image, producing a cleaner image than other antialiasing methods but with a much more significant impact on performance.

 

Bottom line is that the density of the pixels you're actually looking at doesn't change in the slightest.

[KLR Rico]

I think of it as the resolution "behind" the headset is increasing.

 

It's like you're looking through a mesh or screen at a background. At the default 1.0 setting the background image is pretty ugly, but when you crank up the density setting, the perceived image quality is drastically better, even though you're looking through the same mesh.

[JLX]

Actually Pixel Desnity adjustment in the VR Tab only works for the Rift, not the Vive.

 

To adjust pixel desnity on the Vive you need to edit the VRSetting file in the Steam folder.

 

Bumping up the Pixel Density with the slider didn't make much difference on my Vive as you suggested.

 

However, I can't locate the VRSetting file you mentioned. Can you please give the exact path?

 

I'm running the non-Steam version but searching for "vrsetting*.*" in the DCS directories and the Steam directories didn't find anything.

 

Tnx.

[AstroEma]

Look here:

http://forums.eagle.ru/showpost.php?p=2822842&postcount=1

[Gman109]

Does this mean you don't have to go into files and edit them with notepad any longer like this thread below in order to change your pixel density? I have a Vive en route, so I haven't tried it myself yet, but want to know beforehand if I should be going into files editing stuff or just using the "VR options" tab for PD as you said.

It should be obvious what to do.

Actually Pixel Desnity adjustment in the VR Tab only works for the Rift, not the Vive.

 

To adjust pixel desnity on the Vive you need to edit the VRSetting file in the Steam folder.

Obviously not obvious....

 

Thanks for all the help and posts again guys.

 

Both my Vive and Rift arrived today.

Edited August 1, 2016 by Gman109

[steve2112]

What is also important to note is that during the downscaling back to Rift resolution, the resultant image is considerably antialiased already with more intermediate colors than the original had. I'm not sure what shader/hardware algorithm is being applied - and one wonders if that could be further optimized. All I know is that Pixel Density Override has made our first generation VR a much better experience than any AA algorithm could ever have made on the standard resolution.

 

i'm still a bit confused. so by setting a pixel density to something greater than 1, you are creating more pixels than the native resolution is capable of displaying right? then somewhere in the process, i guess the back end of the GFX card, its downsampled back to the native resolution of the rift right?

 

so i guess the question is what's the point of scaling up then back down? (a.k.a supersampling and subsampling)

 

i guess there is a point since i'm pretty sure i can see an improvement in image quality at higher pixel densities, but i guess i don't really understand why. i suppose the answer is here 'What is also important to note is that during the downscaling back to Rift resolution, the resultant image is considerably antialiased already with more intermediate colors than the original had' but don't really get how more detail has been created in this process.

[SkateZilla]

You're not scaling up, then scaling back down,

 

You're Over Rendering and Scaling Down.

 

Scaling up implies your rendering first, then re-sizing larger.

Edited September 28, 2016 by SkateZilla

[Haukka81]

i'm still a bit confused. so by setting a pixel density to something greater than 1, you are creating more pixels than the native resolution is capable of displaying right? then somewhere in the process, i guess the back end of the GFX card, its downsampled back to the native resolution of the rift right?

 

so i guess the question is what's the point of scaling up then back down? (a.k.a supersampling and subsampling)

 

i guess there is a point since i'm pretty sure i can see an improvement in image quality at higher pixel densities, but i guess i don't really understand why. i suppose the answer is here 'What is also important to note is that during the downscaling back to Rift resolution, the resultant image is considerably antialiased already with more intermediate colors than the original had' but don't really get how more detail has been created in this process.

 

 

http://www.geforce.com/hardware/technology/dsr/technology

 

Should help bit, just ignore all NVIDIA marketing bs. Its just Antialising , best for quality.

 

 

 

 

 

Sent from my iPhone using Tapatalk

[v2tec]

does the screen resolution (dcs settings page) has anykind of impact on frame rate with an oculus rift or is pixel density the only parameter?

 

If I choose a very low resolution for the game, will the rift still use it's default resolution and the graphics card load will be reduced?

 

I want the best picture with rift but the picture on the screen is not important to me.

Edited December 4, 2017 by v2tec

[hansangb]

Screen resolution on the CONTROLS page is completely ignored for VR.

[DerekSpeare]

Screen resolution on the CONTROLS page is completely ignored for VR.

 

^ This ^

 

What you set in the video resolution settings is irrelevant. VR resolution is controlled by the VR device. Changing the PD will only 'improve' what you see on your VR HMD. I run DCS at 1.5 and see decent performance.

[Precog]

So how will this work with the Pimax 8k? I presume we set PD back to 1.0.

[Haukka81]

Yes 1.0 is your device normal resolution, no mater what it is, pixmax , Vive , rift.

 

1.2 is 1.2x your device normal resolution (physical pixels in panel)

 

Etc..

 

Think it bit like Antialising , thats just what it is. Brute force method, render image in higher resolution than your panel and then scale it down > less jaggies.

 

 

Sent when im drunk with my iphone near me :)

[dburne]

So how will this work with the Pimax 8k? I presume we set PD back to 1.0.

 

Depends on how Pimax achieves the higher resolution.

Also 4k in each eye does not equate to an 8k resolution display.

[Thick8]

They are already up scaling from a lower resolution. 1440p I think. Don’t know how this will look upscaled maybe it will have an added benefit of some sort of internal color averaging that may resemble FSAA. Who knows, their website is full of impossible unachievable promises.

[hansangb]

Also, there may be limitations within DCS for VR. I was shocked that Odyssey HMDs showed very little improvement. On paper, there are big difference between Odyssey and Rift. But we'll see in due time. 4 more months if Pimax is on schedule.

[v2tec]

Screen resolution on the CONTROLS page is completely ignored for VR.

 

However, the graphics card is rendering the scene for the rift and for the screen resolution. Is that right - so, if you have a higher screen resolution you should consume more gpu power than on a lower resolution, right too?

 

What is the meaning of the fps with the rift? Because it is very low on my site (nevada map, single player, cold start) only 22 - 25 fps. But when I play without the rift, the fps is much higher and gameplay is fluid.

[hansangb]

However, the graphics card is rendering the scene for the rift and for the screen resolution. Is that right - so, if you have a higher screen resolution you should consume more gpu power than on a lower resolution, right too?

 

What is the meaning of the fps with the rift? Because it is very low on my site (nevada map, single player, cold start) only 22 - 25 fps. But when I play without the rift, the fps is much higher and gameplay is fluid.

 

 

No, it just mirrors the display that you see (one eye). VR requirements are much more strenuous, so a 2D monitor may run at 100+ FPS but in VR, it may only run at 45FPS and sometimes 90. Reasons are many and you can google for it. There's also the fact that DCS is still relatively new to VR - all things considered. So it'll take some time for them to further optimize it on their end.

[spetsnaz26]

Also, there may be limitations within DCS for VR. I was shocked that Odyssey HMDs showed very little improvement. On paper, there are big difference between Odyssey and Rift. But we'll see in due time. 4 more months if Pimax is on schedule.

So, given that the Odyssey has higher resolution, does it mean that we need a lower PD to achieve equivalent quality? Taken to the extreme, once we have retina PD VR, there's not much gain to go above PD =1 In DCS, am I correct?