RMT Textures (Roughness, Metalness and Transparency Maps) - Ezekial711/MonsterHunterWorldModding GitHub Wiki
RMT files stand for Roughness, Metalness and Transparency mapping.
This is an RMT file for MHW:
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Each channel corresponds to one of the properties.
Red correpsonds to Roughness. This is an example of a MHW Roughness texture:
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Lower values will indicate that the surface is glossy, while higher values make the area more matte. The curve is not uniform on most of the samples I have checked. it's very aggressive around the 200 mark. 180 and 220 are EXTREMELY different compared to 140 to 180 for example and the converse also holds at 220 and 255 being extremely similar.
An important note about Roughness, Red channel will turn the surface into 100% glossy, meanwhile a full white red channel will turning Roughness to 100%. It's the best to never use 100% white unless you want to apply it on baked shadows (like the inner barrel of a gun shadows).
Green corresponds to Metalness. This is an example of a MHW metalness texture:
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This applies a dark highly reflective tint to the area. The higher the value the more it's darkened and the more it will reflect.
While it's true, it makes the area darker, it has a reason. It literally is the metalness of the object. White = the area is metallic, black = the area is dielectric. Since it's PBR (physical base rendering) this will make an impact on how the light is reflected, thus making it "darker". Usually areas that are metallic are painted with very light, desaturated colors in the albedo.
The biggest difference on darkness and metalness applied happens from 50% white to 100% white on the Green Channel.
Blue corresponds to Translucency. This is an example of a MHW translucency texture:
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Translucency is used often in World on Fur and Bone surfaces, which is what gives it some of its style.
The recommended value for Translucency is from 0.01 to 0.7, higher than that will turn the surface very bright.
On top of the mapping the way the mappings are applied (roughness radius and green darkness tinting) are also controlled by the mrl3. Different mrl3 have this values in different locations within the material's float array.
Alpha corresponds to Subsurface Scattering. This is an example of a MHW Subsurface Scattering texture:
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This is used for setting a gradient limit on the Translucency texture (Blue channel). We can see it on Velkhana's wings, so if we see them against the sunlight the tips of her wings seem translucent, meanwhile the center and closer parts to her body are less bright.
We can see an example of this on a Petal:
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It's important to point out that Alpha channel will also consume any lightning on the surface created by EFX and any type of visible auras, an example would be the Dual Blades Gauche Glowing or a Hammer during charge. The amount of light absorbed will depend on the intensity on the Alpha channel. This makes Subsurface Scattering more important for creatures, like having a Deviljho with "Base Emissive Color" setting turned up on the MRL3 plus subsurface scattering, so the internal emission is also spread around the skin giving it a living flesh effect.
The Alpha Channel can easily clash on the Translucency channel, creating a rough difference of light between where there should be Translucency or Subsurface Scattering so it's best to avoid overlapping both maps by slightly creating a shade of black in between both.
The recommended values for Subsurface Scattering are from 0.01 to 0.5, higher than that will turn the subsurface into a very noisy red blur.
RMT with Alpha channel must have the same DDS format BML Textures has.
We would recommend to not use subsurface scattering higher than 0.2 unless you're working with organic creatures, Translucency can help alone on any armor and weapon.
Credit to Ezekial, Asterisk, Starflare and Akkokoro