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Resolution vs PPI vs PPD Explained - Which is best and why for VR

Level 5
Hi all,

There are 3 terms I've seen floating around the past couple of years, namely resolution, PPI (pixels per inch) and PPD (pixels per degree), that manufacturers use to sell us their hardwares on the basis of image/screen clarity.

Resolution is ok as a rough guide, but not the best spec that outlines how clear and image in your VR headset will look.

I've been taking notes on my VR journey and pieced together this tutorial which outlines the differences, pro's, and con's to the above terms, and also the other factors that can impact what quality the VR image is that you see at your eye:


Level 8
you count the aspect ratio starting at the center of the screen, then count in units up and sideways in the positive numbers of the x and y coordinates.

then you fill in the units with pixels. the xy ratio can be 16:9 ratio, 4:3 ratio, etc.

then you have the size of the screen which affects the size of the units. too large a screen and the sprites in the units get too small to see, if the screen is too small the sprites in the units get too large to be useful.

thats what i got from a course im taking i dont know if i got anything wrong, heres my take on that info.

you need the screen size to be large enough to take the aspect ratio units so the sprite pixels in the units dont show the screen door effect.

Level 9
This video started great but ended badly. This would have been a great video in 2017-2018, but for 2019 most headsets releasing now are RGB stripe LCD headsets (so it should be explained why that is, and what the RGB stripe brings to the table). You only briefly mention 'subpixels' and 'RGB stripe', but don't explain the impact they make on clarity in your video.  And that PPD table by Heaney is old (I believe he made that in 2018)

Without this explanation of subpixels, then we'll still have users with their Oculus Quest or Vive Pro claiming their headset has just as good clarity as a Valve Index since both are 1600x1440p displays. In 2019, subpixels matter.
i7-7700k, Zotac RTX 3080 AMP Holo (10G), Oculus Quest 2
Previous: Oculus GO, Oculus RIFT - 3 sensor Room-scale, Oculus Rift S

Level 5

ShocksVR said:

In 2019, subpixels matter.

Couldn't agree more.  That said, this video is designed as a top line overview and understanding of the basic concepts behind the relationship between resolution, PPI, and PPD.

I mentioned sub pixels at the end as a recommendation for viewers to look in to that as one of their next topics to understand.

What I didn't want is a video with all the detail resulting in an overwhelming volume of content for new comers to the subject, its just too difficult to retain in one initial hit.  In hindsight though I could have highlighted sub pixel arrangement a little more as that would be in my mind the next progressional piece.

Think of this video as the start of a journey of understanding for those who want to dive deeper in to the topic.  Or for those who are happy with only the broadest of overviews, just that.

Thanks for your feedback mate, valid.