I noticed (several times) in the videos that Specular was reduced to make materials less reflective, rather than increasing Roughness. I seem to remember from some PBR instruction that Roughness was preferred. Is this significant at all?
Hi techworker1 ,
Simplifying this a bit, but:
the idea about reducing the Specular, is to make the material less reflective, where as increasing the Roughness 'spreads out' the reflections (makes them less mirror like and therefor they seem to be reduced, but the total amount of reflected light stays the same).
I'd say in the end, it's CGI it's all fake anyways, if it looks good and cool you're ok. I remember one time Bartek Skorupa gave a demonstration on how to make a gold material in Blender, with all the scientific real world values for IOR and fresnel and it was a crazy amount of nodes and math. He rendered it and it looked amazing, real gold practically. Then he said now look at this, this is a standard gold material, normal fake CGI, nothing to it, he rendered it and it looked 99.999% exactly alike. He was like see? there's no need to go crazy, when it looks good it's good enough.
techworker1 great question. Conceptually, yes, increasing roughness to 1.0 has a similar effect to a specular value ("IOR Level" in 4.0+) of zero. It's hard to tell the visual difference in the renders below, but the one with specular at 0.5 and roughness at 1 (A) is a touch lighter from the reflection. Overall I qualify the difference as barely noticeable.
(B) is the same except for specular (IOR level) at 0.0 for all materials. Notice how A rendered slightly longer at 9.42 seconds compared to 9.29 in B. The thing to consider is that reflections take longer to calculate. It's quite a small difference in this simple example but if you have a scene with hundreds of objects with 1.0 roughness reflections, it could be quite significantly longer render times or noticeably more noise in the results.
My practice is to leverage a 0.0 specular value for objects that appear "entirely diffuse" or "matte" rather than a roughness of 1.0. In fact I rarely use roughness above 6.0 because reflections get very subtle beyond that point and it's not worth the extra render calculation. BUT I wouldn't deny a claim that higher roughness is technically more accurate than specular at 0.
I hope that helps clarify!