Baking for RT Render Engines explained
One of the common misconceptions about baking is that people think they can use a render engine to "bake" materials for game assets.
In reality you can bake only certain aspects of a material into a texture. These are obviously diffuse maps, normal maps, displacement maps, ambient occlusion maps and certain hybrid forms of them ("albedo" as a new term for "diffuse + light/shadow values", for example). Furthermore you can bake certain "helper maps" to help a RT render engine to generate physically based or dynamic aspects, like specularity and lightmaps.
Specularity maps are black and white or greyscale images that are are processed by any real-time render engine where black is interpreted as non-specular while white represents the opposite on that scale. They work, similar to normal and displacement maps, as non-color maps.
Lightmaps are similar to ao maps a static representation of light and shadow and their primary use is to reduce the GPU load on shadow calculation.
Other material aspects like transparency, translucency, reflection and refraction of glass-like materials cannot be "pre-baked", since they depend on the render engine's capabilities and techniques to generate them. If your game render engine is capable to recreate these effects, they have to be created in the game engine's material editor.
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