is 4% reflectance value is in linear or srgb?

HapZungLam2

Here is one of those confusing topic again.  I remember I've asked long ago how come using substance designer to convert from metal/rough to spec/gloss the spec value is grey.  And someone has answer it is because all object has spec and its 4% in linear and 2% in srgb (or the other way around)

Assuming my render engine will "add" gamma to any linear input(image get brighter when I set the input as linear).  Do I still put 4% gray on my spec/reflection map? or should I degamma that to 2% (or simply set the input as srgb)

EarthQuake

4% linear is the reflectivity value of most insulators (non-metals). in sRGB that would be #383838 or 56, 56, 56.

Whether your engine loads the texture as linear or gamma space (sRGB) is generally up to you. So use the appropriate value.

This tutorial may help: https://www.marmoset.co/posts/pbr-texture-conversion/

HapZungLam2

is that mean If my reflection map set the value as 56.  In my render engine I should set as srgb(because if I set as linear it'll add gamma)?

EarthQuake

Yes, if your 4% is set to 56 that means you're authoring the content for sRGB (gamma space), so the texture should be loaded as sRGB. If you loaded it as linear space it would not apply gamma correction, which means it would be 22% rather than 4%, which would be incorrect.