Question about Metallicity
Nyghtfall3D
Posts: 764
I want to be an expert Iray user, and am currently learning how to create Iray shaders.
My understanding is that Metallicity overrides every other property except Refraction Weight. If so, then why do the DAZ Uber metal shaders that come with DS use Glossy Roughness?
Post edited by Nyghtfall3D on
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Okay, metallicity does not override things, per se.
What it does, is determine whether a surface is dielectric or not.
Black on a map, or 0 setting: Not a metal. This means reflections, etc, do not carry the hue of the item (the Diffuse / base color) through any shiny reflections. For example, an extremely polished boot or shiny plastics.
White on a map, or 1 setting: A metal. This means reflections fo carry the hue of the item. For example, actual metals.
The Glossy Roughness is exactly that - how rough a surface is. A 0 is pretty much a perfectly smooth surface, such as a mirror, or an incredibly polished plastic, or even the surface of a still lake, while a 1 would be something so rough that very little light reflects off of it directly towards the observer.
So, a Metallicity 0, Glossy Roughness 0 would be a mirror, nearly obscenely polished shoes, or the like.
Metallicity 0, Glossy Roughness 1 would be something that has pretty much no direct reflection. Even, say, suede has at least a tiny amount of direct reflection, so a 1 here is rarely, if ever, used.
Metallicity 1, Glossy Roughness 0 is some form of metal polished to the utmost degree, and Metallicity 1, Glossy Roughness 1 is a scoured, crude ore (again, there's usually some form of direct reflection).
There is a big contention as to whether fractional values of Metallicity should ever be used. To put it simply, in the real world, surfaces are either dielectric or they are not. However, I hold with the camp that says some areas can have fractional values or gray areas on a map, because the surface area covered by one pixel might cover, say, fragments of dust on a metal surface, or a fingerprint, or some other imperfection too small for a single pixel to represent where both dielectric and non-dialectric surfaces may exist.
And just as an example, this is an old chart from when PBR materials first started being a thing:
I'm definitely learning. I understand all of that. Thank you. :)
I also just discovered a crucial aspect about the DAZ Uber shaders. They use Weighted mixing mode, which is why the Glossy Roughness setting works. Glossy Roughness has no effect on Metallicity when using PBR Metallicity/Roughness mixing mode. I forgot to check which mode they used, and that's what confused me.
enter light
exit night
take my hand ....
oh Metallicity doh!!!
yeah more reflect light
sorry had to go there
My understanding of Glossy Roughness is it controls how widely the rflection is spread - high values still reflect light, but any point reflects a bit of the incoming light in a spread of directions while low values reflect the light mostly in the opposite of the incident angle, so low roughness gives small, bright highlights from light sources while high roughness spreads the highlight out make sit proportionately dimmer - as the image shows.
Roughness governs the effect of extremely small scale bumps on a surface. You can actually produce the same look if you use 0 roughness, put in a noise map for bump, and set tiling to the bump to a very high level. Mind you, you are better off just using Roughness, but it illustrates the principle.
It would also be very impractical... not sure about iRay, but a lot of render engines would either suddenly take many times longer, or beyond a certain point simply stop rendering the bump.
Although if one were a purist, one could argue that Roughness is a shorthand and so it's not REALLY a totally physically based renderer...
(Though down that rabbit hole one could argue that stuff that doesn't simulate atomic structure isn't TOTALLY...)
Yes, that's what I understand.
I actually tried it out at one point to verify it. Among other things, it impressed me with how well Daz's implementation of Iray can handle some realistic elements.
Another example is that Caustic filter does a surprisingly good job at handling prismatic color separation, and also another principle I forget the name of where once the angle hits a certain point the light starts refracting back into the object and doesn't transmit.
Wish someone with access to a comprehensive electronic PBR dictionary would refine and publish it. While that chart is nice doing things like showing a color without it's RGB or other standardized written value isn't that helpful.
Is there such a PBR dictionary for sale somewhere for the most common, say 10,000 materials?
Closest thing I've found is an sRGB chart on an Asian Twitter post. When I entered the sRGB values on the right in the corresponding channels in the Base Color, I got surprisingly well-matched results.
Of course. I'm waiting for the version of Iray where you specify the atomic structure of the surface and it uses quantum electrodynamics to work out how light is reflected from it.
Thanks.
You know, it makes me think about plugging in those values for nonmetals. Huh. (Like Coal)