Green coloured Normal Maps and their usage?

[3dwannab]

See attached.

One 'Normal' Normal Map and a green coloured one.

What's the RM in the name mean and what use would these have?

DL'd from here: https://gumroad.com/andrewalexart

[romullus]

Sometimes normal maps can be saved without blue channel, but never without green or red channel. Your example is greyscale map, it's just saved into single green channel. Can be used for mapping reflection, glossiness, displacement, bump, etc. But it can't be used for normals for sure.

[3dwannab]

Cheers. I can't find any info on how to use them as you describe. Just slot that into the reflection, glossiness, displacement, bump slot without any additional utility map between?

[romullus]

Probably yes, just plug and it should work. If you're not getting expected results, then try to fiddle with bitmap parameters in bitmap node.

[3dwannab]

I will. Just never came across them before.

[3dwannab]

Invert the map and just mono'd it with a CC just to have it greyscale. Works a treat.

[romullus]

If you'd skip CC node it would render exactly the same, just maybe slightly faster ;]

[3dwannab]

I'd say so, but I like to stick one in just to see it in greyscale.

[Eddoron]

Sometimes when you download maps, some of them might look fine at first glance but were intended for game engines.
When inspecting them, they have a funny colorization and that's because multiple grayscale maps were stored as RGB channels to save space.
R could be specularity, G the roughness, B - AO.  Inspecting them in PS or an advanced Image viewer can tell you more
TGA is often used for that purpose.

If I'm not mistaken, Quixel "materials" also use that approach.

[3dwannab]

That make sense. Thanks.

So the RM appended to the map name could be roughness and metalness ?

[Eddoron]

Seems likely. I haven't touched any game engine for over three years now, don't know if there's a specific order, but I'm certain that those are for game engines. In Unity 4, the spec channel had to be an alpha in the diffuse IIRC. (at least that was how the KSP shaders worked)
On his Artstation page, he said it was created with Substance Painter. I guess he exported it for Unreal or some other engine.

I've just downloaded the free material pack from the site and one file has R_M_A at the end.

Btw, the rock's blue channel:
edit: I've taken two channels of one "R_M_A" image which has very different structures and put one above the other +scribbled a mask for a better illustration

[maru]

According to this post, maps ending with _RM could be metalness or roughness (the latter one makes sense - "Roughness Map").
https://blenderartists.org/forum/showthread.php?435072-Need-help-identifying-Texture-map-types(not-diffuse-normal-or-specular)