Hello. This thing comes up a lot when I work with megascans asset, and I don't really understand why it is. Often times, I get the best result if I put the roughness map into srgb color space (in Unreal Engine). Especially on foliage, but sometimes on other type of assets too. Why is that? Is this normal and I miss something? From my experience, anything grayscale should be set to linear color in PBR. I am not using the quixel master material by the way.
The only reason you set grayscale textures, or anything used for math, to Linear is to tell the editor to not apply a gamma correction to put it into linear but instead use as is during the rendering process. This can break depending on the file format, since a format like PNG usually applies it's own gamma, which reverses everything. I think Megascans textures are always JPEGs though, right? Maybe try opening it up in Photoshop and looking at the values with various gammas of 0.4545 or 2.2 to see if they look more like what you'd expect for that surface type.
Edit: It may also just be a case of human error if it only happens with a few surfaces, since they are all still manually processed iirc. But they're quick to fix them if you can provide the jumbled name associated
Roughness is srgb:
Roughness is linear color:
I checked out how much shiny is this plant in real life, and actually it really varies, so maybe both look could be correct-ish. However... To get similar results to the example renders on the Megascans website, I almost always need to use srgb on the roughness map of them. For example, to get this guy looking similar, I need srgb on:
I get this with a lot of the 3d plants. It isn't a big issue, because its one click to change the color space, I just wanted to know if this is intentional and there is a reason for it.