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MSFS20 Roughness Clamped Values

L

LioC18

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24
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us-illinois
Hi,
Something I don't understand is the way how the MSFS Engine is dealing with the roughness.
Looks like the roughness values are clamped. It is not a full range between 0-255.
I presume it is related to PBR physical correct values and computation optimization (less data to compute if you use a range from 50-200 instead of 0-255?).
Do we have some information about the math behind this and if it is "only" a clamp or something like a curve remapping?
 
I think you have to do the experiment.

Attached picture changes roughness and metallic values by 25 each time to produce a grid of 11x11 balls with all values between 0 and 255.

With regards to roughness there isn't much difference between 225 and 255 (full roughness) but there is a difference (although very slight). At 200 you really start to notice the specular highlight starting to form. At the other end of the scale there isn't much difference between 0 (no roughness, it's smooth as glass) and 25 but you can notice at 50.

There are differences but you need to load it into the sim to see.
blendervsmsfs.jpg


Keep in mind each ball is a change of 25 in the RGB values of the metallic/roughness texture. In the second column you can see how a little less metallic has changes the color of the sky reflection. As you go up the rows the rougher surface makes the sun spot reflection larger.
roughness1.jpg


At the rough end of the scale there is a very slight difference between full rough and the next row to the left. It's subtle but you can start to see the sun spot affect the color. In the next row it is more noticeable.
roughness2.jpg


However, in this corner where there is no metallic and no roughness the changes are a lot harder to spot.

roughness3.jpg


I don't think there is clamping of the values. But there are situations where the change is virtually undetectable. In the no metal, full roughness corner changes are imperceptible. As you increase the metallic value the specular reflection becomes more noticeable at the same roughness values.

To appreciate the differences (and effects) you really need to do the experiment.
 
Just for fun, here's the same balls but with a mid grey base colour (compared to the full white in the previous set). I think you can pick up better how the second roughest row (roughness value 225) is starting to develop the specular highlight.

roughness4.jpg
 
@Anthony31 Thank you for your explanation.
This is something I should have done.
I was testing with a single object and tweaking the values but having this spheres pattern is a better way to see the difference.
It is a bit sad that we do not have any technical information from Asobo.
Thanks for your time
 
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