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Untold Digital avatar image
Untold Digital asked ·

[aiStandardSurface] Should Base and Specular weights always equal 1?

I've noticed in some tutorials that the author says the Base and Specular weights for the aiStandardSurface shader should always equal a value of 1 because surfaces shouldn't give off more light than they take in. This makes sense but when I load built-in presets such as Car Paint or Plastic or any of the others the Base weight and Specular weight are usually both set to 1.0 thus equalling a total of 2. So what is the correct operating procedure here? Also, when loading a texture into the Base color I've heard that you always set the Base weight to 1 is this correct as well?

shadersshadingstandard surface
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Mike Farnsworth avatar image
Mike Farnsworth answered ·

For the old, deprecated standard shader, that was true; you needed to make the weights more or less add up to 1.0 yourself. However, for the new standard surface, standard hair, etc shaders they are always energy-conserving and so you don't need to worry about the weights adding up to 1.0. They use a layered approach, where each layer will modulate the one beneath it, not allowing energy to exceed 100% at any point. You can set those weights to anything you like in the range of 0.0 to 1.0 for each layer.

When linking a texture to the base color, if you set the base weight to less than 1.0 you will darken your textured base color a bit. There's nothing wrong with that, unless you didn't expect any darkening of course (and in that case, set it to 1.0). The default base weight is less than 1.0 because in the real world there are not matte/diffuse surfaces that reflect 100% of the light that lands on them; there is always some energy loss. If you've baked that slight energy loss into your texture, then you'll want to set the base weight to 1.0. If you haven't, and you have some pure white areas of your base color texture, then bumping down the base weight a bit to 0.9 or 0.8 is recommended just for realism's sake.

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Thanks very much for the excellent clarification!

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Mike Verta avatar image
Mike Verta answered ·

On this - is there any difference between lowering the weight value, and lowering the color? i.e. is base color white of value .8 the same as base color 1 with Weight value .8? Advantages/disadvantages?

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They respond the same, I believe. Lowering either one should achieve the same results, which is less contribution from that layer.

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