This is something I have searched on the web. Say we find a good texture of smudges or scratches from the web and we also want to generate a normal map from it. I know there is a gimp plug-in for it but I would love to see how cgcookie masters go about it. If there is already a course or tutorial on that please point me to it!
Also is there a reference (like the ones we have for Fresnel values) for roughness of various materials or we just eyeball it?
Hey Sinnay, good questions! For creating a normal map from an image I generally use Bitmap2Material since it comes with Substance, but if you don't have that then I'm sure a Gimp plugin would work for basic stuff like scratches.
There's not really any good chart for roughness values (the one's for Fresnel aren't all that useful either unfortunately, the index of refraction values are different than index of reflection), so you just have to eyeball it. Use lots of references though, so that it looks as accurate as possible. Good luck!