Shouldn't diffuse maps be 100% free from shadows?

Hey guys,

So, I’ve learned that diffuse maps should contain only the color information. So I presume they should’ve zero shadows or reflections.

However, whey you see a diffuse map of a character, especially the face, you never see a completly uniform skin. You’ll always be able to see the borders of nose for example. But in the real world, the skin the sits on the “border” of our nose isn’t any darker (except by the presence of shadows) than the rest of our skin.

So, why it wouldn’t be a good idea to make the diffuse map 100% free of shadows or fake borders?

Technically it is correct to have no lighting information in albedo. However due to technical limitations in some case having small bit of lighting information in textures can improve the look a bit, more so in realtime renderers where the lighting model still fails to account for smaller details, however that comes at the cost of looking wrong under different lighting conditions that the textures have baked into them. Unreal has a AO map input that’s the correct way to add AO to materials, where the renderer cant.

In offline rendering, if you just use normal / bump map with no displacement you can end up with cases where there’s lighting mismatch due to geometry not being detailed enough. Having the lighting information baked in kinda helps with that. That’s how the Ian Hubert popularized photo projection style can get away with simple geometry.

For skin there’s actually lot of variance on skin color so from reference I’d say that the skin around the nose (and in deeper wrinkles) is different color. Might be AO too.

Edit: Some cross polarized photos for reference: