Compression settings for roughness/grayscale maps?

Hello. Primarily I want to know which compression settings you should use for a grasycale map such as roughness or metallic. I’m assuming default just saves 3 channels of the same value practically wasting space but what’s the difference between ‘Alpha’ and ‘Grayscale’? Does grayscale still contain 3 maps but when all combined provide a black and white result?

Also what other settings would you manually have to change on import? I’ve noticed sRGB should be disabled for roughness and normal maps.

Hi, first of all, id like to know, what you mean by grayscale map? You got some textures, but in which format?

We are using a 32bit .tga (with alpha channel) or 24bit (without alpha channel) format with RLE compression. Targa is lossless and really bad for images, but very good for icons and such things. (I’m not sure but I think Unreal is applying a RLE compression by itself after import).

Lets say you have a mesh without alpha, you have a albedo map, a roughness map, a metallic map, a aspecular map and a normal map. Thats a total of 5 textures.

Albedo and normal map do need all 3 channel (most time) but the other 3 only use 1 channel.

So you can create one texture in Photoshop or whatever, import your metal-map, change the color to 255,0,0

Import metalmap, set the color to 0,255,0 and the specular to 0,0,255.

Now you can import your newly created texture and use separate pins for the materials.

Here we have a brown leather Material:

To be honest, I’m not quiet sure what you exactly wanted to know, and I think I missed your question because I inly know my workflow, but I do fine with sRGB

Thanks for answering but yeah it doesn’t entirely answer my question. I use .tga format for all my textures exported from substance painter and or photoshop. Photoshop exports are in 24 bits/pixel and substance painter only has an option for an 8 bit export, I’m assuming this is 8 bits per channel.
Secondly, yes I know you can combine roughness, metallic and specular into a singular texture but I rarely need all three. Mostly I often just need the roughness map on its own. If I were to import just the roughness into the engine as a single texture which compression settings should I use, if it even makes a difference. If you don’t know which compression settings I mean, they’re in the details panel when you open up a texture in unreal.
Primarily I just want to know whether having this single roughness map as a texture will take up as much space/memory as a diffuse map that has all three channels filled or does unreal automatically handle this part when you export your final project?