Bump Roughness was created for efficiently sampling micro details in Cars 3. With this pattern, RenderMan automatically switches from a bump map to a roughness value depending on the size of a feature in the camera, effectively improving  your render times by lowering the sampling rates needed to render such details.

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A crucial feature of Bump Roughness is to keep see micro details when objects are far from the camera, as shown in the example above. In the example above, you can see how we can get very close to the intended look-development with only 1 sample, instead of having to fire hundreds of rays to find the intended features in the textures.

There are many other types of materials that benefit from the added detail that Bump Roughness maps bring, such as carbon fibre, metals, plastics, and fabrics.

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