Metallic gray values when adding grime to the top of metals.
I have confused myself with how metallic maps work. So I have a pbr correct brass that I have made. I want to apply some dirt over the top of it while keeping my metal map black and white. If I have the metal material property turned on and fully black, my mask still has gray scale values which creates gray metalic values which I don't want. is there a way to make all grayscale metal values black while still keeping the gray scale values for my color and roughness? Or is it ok to have gray metalness values where dirt is?
metallic map with dirt
material view
Replies
Well. in our renderer ( not Unreal) I always use gray values because otherwise it's so strong halos it looks super ugly. It also depends on texel size. With smaller texels size that halo issue is less noticeable .
Besides white values are only look nice for clean metal IMO. Subtle amount of dust or dirt cover makes it something in between .
For that kind of rusty pipes I usually just make something 50% gray flat fill with a few random white spikes. and if it's a metal painted over it's not a metal at all . The best approach although is making a desicion based on how it rally look in your target game with a few different lighting conditions.
Thats great to hear, was getting quite confused about all this stuff online saying gray values are a no go. Thanks for your help Gnoop!
every pixel in a texture represents coverage of a certain area. if you're at a texel density of 512px/m a single pixel covers approximately 2mm square.
2mm is significantly larger than a particle of dirt so you cannot represent each particle accurately. Because of this, each pixel must represent the average amount of dirt in a 2mmx2mm area. This is absolutely going to be some sort of grey value unless the area is completely clean or completely dirty.
This does not mean its ok to use a semi metallic value to represent car paint or solar panels - those need proper shaders - it does mean you can use grey values to represent partial or thin layers of dielectrics on top of metallic surfaces and its not even a hack.