This is something I’m sure has cropped up before but I’d like to see the thoughts of the dev’s & end users on this.
If it’s not in the pipeline to be implemented what would be an ok work around for now ?
A sort of mini disclaimer, this has only really cropped up due to my EXCELLENT fxphd class with Rob Harrington (MYA214).
So I’m not claiming to be an expert on this, only that I can see the benefits of having this implemented, and if not, how we can get close enough.
Just a recap if you’ve not used MR for some time.
Under the BRDF settings in the MIA material you can choose between Fresnel, or unchecking that and using what seems like the Schlick implementation instead.
Why would you want this ?
It’s purely for better control, more so if we can input the numbers ourselves (like the MIA mat), and especially useful for metal approximations compared to Fresnel.
Simple IOR - Fresnel (plastics/wood/organic )
Complex IOR - Schlick/Custom (metals)
Now this isn’t in anyway to suggest that work done so far doesn’t look good, of course not, just that this would be a good addition to have in our vray toolkit !
If you check out the graphs below, you’ll see it a bit clearer what is going on.
(permission has been granted to post screen shots from my fxphd class)
In this first graph, using pure copper as an example, and some data from http://www.refractiveindex.info
The Wavelength values have been changed in accordance with our R/G/B values (top left of the graph) before generating the n (Refractive index/IOR) and k (Extinction coefficient/K) values.
This data is then represented in the corresponding red/green/blue curves in the left graph.
The ‘Schlick’ value is just flat lined to make it easier to see what’s happening in this first screen shot.
In this second shot, we want to get the Schlick curve following the red curve of our data, as close as it can be.
Not bad, it’s pretty close.
Now in this final screen shot, I have reset the Schlick curve to flat line again and now have edited the B curve (just to show as an example).
Of course, now I’m trying to match the blue curve to the red one.
You see where it’s value in the IOR box is at 60 - but look at the curve and how it drastically dips !
To visualise that, the reflections would be getting weaker, right until the final angle of it, then it shoots back up to 1.
So that number is like us in VR setting the Fresnel IOR to 60 (just so you know what I’m on about).
Of course these numbers are for very pure materials, and we’re likely to have scratches and other things messing it up. It’s merely a guideline and interesting to see what is going on.
Something I know a few people would like to see implemented, for us to have some kind of control over the BRDF, if that’s not going to happen - is there a way we at least get a little closer ?
I did have a brief chat with Dimitar ‘Jimmy’ Krastev last week in London about this but it seems like 3dsMax perhaps has something but not Maya unfortunately (yet).
