Bump Roughness was created for efficiently sampling micro details. 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. 

Simply use traditional bump or normal maps and the Texture Manager will convert them to Bump Roughness textures automatically. You'll notice your newly created tex files now have a b2r suffix after the file name, such as myTexture_b2r.exr.tex 

© Disney/ Pixar

One such example is Louise Nash (shaded by Yeon Kang) from Cars 3. Here you can see extensive wear of the clear coat on the paint job, which creates micro-scratches and breaks up the specular in interesting ways, also driving the anisotropy in ways which more accurately reflect the intended look-development.

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