There’s the visible part of the panels, which @Sjef found out in his teardown being 75%-77% of the panels.
The subpixel size stays constant no matter what FOV is used, the magnification also is a constant amount and does not vary.
The subpixel amount varies depending on FOV (FOV settings change the amount of rendered subpixels, they’re still visible through the lenses), but that’s irrelevant to the figures I presented, as the first PPI figure takes into account the whole screen size, and then alters the value depending on whether it’s pentile/rgb, and then once again to factor in magnification.
Hidden area mask and invisible portions of the screen are irrelevant when we’re talking just about the visible subpixels on the screen (which do not change in size)
Yes the FOV cuts off some rendering in the visible range, but we assume the whole screen is the PPI value and rendered subpixel value, and then factor in visible screen amount to determine Magnification amount (and perceived loss in pixel density in the last PPI value for Pimax, and the visible rendered subpixel amount is also extrapolated from the visible percentage of panel utilization (75-77%)
Magnification affects the perceived pixel density, which is why the PPI value is adjusted once again, with respect to sjef’s findings on visible screen space.
In other words, the magnification amount is constant and the visible subpixels (77% of the screen you can see in the lenses) are the same size as the whole screen in fact; but perceived pixel density is less because the magnification occurs, so the PPI value after magnification decreases the PPI by roughly 1/4, to take into account the decrease of perceived pixel density as a result of magnification.
With regards to the discrepancy in viewing distances to take photos, some discrepancy may exist but I wouldn’t discount any findings solely on that basis as those discrepancies are likely small enough to be attributed to human error and they would not greatly affect the result
(in statistical analysis in journals there is always a few margins of error allowed)
I agree that PPD is a useful metric (but difficult as you need to know panel utilization for all headsets and viewing distances between screens and lenses for each. which is different for all HMDs).
As vertical PPI is the same for pentile and RGB screens of the same size and resolution; Vertical PPI may be useful to compare wide fov and small fov headsets, but I don’t see much point in comparing pentile to rgb if it’s the same measurement of pixels vertically (This is why I think diagonal PPI is useful for comparing pentile and rgb screens with the same diagonal measurement (5.5 inches or 3.5); and for comparing headsets with similar resolutions (in total subpixel amount, … > 5 million - 10 million)
It’s not really useful when comparing a 5.5 to a 2.5 inch screen.