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@Szark .... .
PBR formulas use linear colorspace... in linear colorspace 50%grey from sRGB has just about 22% black...
if you have 50% black in linear space and convert to sRGB it is about a 188 grey..
.
This is one of the most confusing parts of correct PBR mapping in Iray
if you like to stay in s/RGB because you know it allready (standard)... then you paint your map with normal greys in 8 or 16 bit.. then apply a gamma correctur of 1/2.2.. this comes approximative closest to real linear color space...
you can convert to linear also just by switching IMAGE-MODE to 32bit image formats BUT ->
Because software and montitors use allready gamma corrections too - you wont see a difference in Photoshop while converting from 8 bit to 32 bit.- 32Bit.image formats are always linear! And look darker - it is there but you cant see it - you will have wrong colors in your map (just 22% black instead 50%) - you can not see that because photoshop corrects the differences automatic by standard) you must switch OFF color profile lock corrections (CTRL - Y on/off) and then you see the difference and understand why you are NOT linear to 1-100 scale coming from a painted sRGB/Jpeg map.
This charts which you usally can see using marbles from 10 - 100% .. and a grey gradient scale ... are also tought to PICK colors...to create a material using values somehwere on the gradient.... but you must make sure that you are in the correct color space to make this working!
I hope you didn't had a hangover I think you've had.
About reflectivity on PBR Metallicity: I looked into the MDL and also read some about Fresnel, There's nothing wrong with reflectivity. Your understanding of the 0.00 value is, that this would mean the material isn't specular at all. But that's not that correct. In our physical world, everything has Fresnel and everything is specular.
The Glossy Reflectivity parameter of PBR Metallicity simulates diffuse (loosing the image, blurry) vs. specular (mirror-like, sharp) due to Subsurface Scattering capabilities of a translucent dielectric material. At 0.00 you have much diffusion, at 1.00 you have much reflection. Since metals are too dense to be translucent, the parameter doesn't have any effect when Metallicity is set to 1.0.
In your test example you have a roughness of 0.00, a perfect smooth surface then. At reflectivity 0.00, the reflection on the center of the marble is gone, due to the diffusion. That's the correct behaviour. You reclaim that there still is Fresnel reflection visible and consider it wrong. But in fact that's also a correct behaviour (for a perfect smooth surface). On a perfect smooth surface, the outgoing angle of a lightbeam is the same as the incoming angle. The reflectons which irritate you are caused by lightbeams striking the surface at a near 90° angle (grazing angle, F (90°)). At this angle the absorbing and scattering capabilities of a material can't come into effect, since the beams doesn't penetrate the surface, and so have a lesser to none impact on the specular reflection resulting in a strong reflection at the rim.
@Arnold C.. overthinking our conversation about what is broke in iray...
....
something was really "broken" in my iray system and can't think of a logic reason what and why... but it looks as it was just to me - so i start to nail it down on my hardware/iray config?
Whatever it was.. it seems now to be fixed since i updated to the latest Beta. And not just in the Beta, also 4.8 is now also fixed`hhmmmm.... no chance anymore to replicate the out of world white marple example (spot reflections with zero weight - roughness clearly there - but not on fresnel) from above... this strange behavior lead me to weird conclusions/guessing such as reflection has allready also roughness included (in iray)... it was not just the wine - the proof about my broken pbr metalicity iray at the time of our discussion (and also the weeks before) is above in the white marble
Fresnel... yes..that's why i said limitation..(in iray)... other PBR engines have more parameters for this effect .. in iray it is just there based on weight.
Anyway - since it seems i have now the same render results as you do - just now i can try to replicate the conversion metaliticty/specular differencens which you showed.
Yeah I am so used to working in sRGB for so many years. I will get used to it. Thanks for the explanation yeah it is linear when you put it like that but I should have said not linear in terms if sRGB
Terminology... talking about PBR IS difficult because of different meanings/terms to describe the "effects" and parameter...
in common language/tongue: Glossines describes allready the "whole" effect of glossiness/reflectivity/diffuse/scattering... and reflectivity is just another word for the same...
in other PBR forums some refer to smoothness = roughness AND reflectivity.. or shine = the whole effect, aka all needed parameters including diffuse roughnessand SSS and so on.. this seems to me one of the best possibilities.
From now on i will try to use only smoothness and shine to describe what i am talking about - as i am a non native english speaker and new to PBR : question .. is this correct?
well in a PBR sense I would refer to roughness which donates both smoothness and shine.
what about:
smoothness as a independent term from the PBR workflow to describe only the parameters roughness/glossiness ?.. some game engine do so i think.
Out of my stomage i used "shine" and "highlights"... to point on different areas of the full effects on a final render. i used shine for "areas with roughness scattering, diffuse blurring" - highlights should be clear i hope..
Well still not sure.. thx Szark.. other opinions ?
game engines, Unreal 4 use PBR Metal/Roughness only, Unity does both PBR Roughness and Specular so for me that only uses PBR Metal/Roughness I will keep to the term roughness and reflectivity.
right good hint - those which work just using the MR workflow (a lot of the stuff in web).. have lesser problems with terminology..
They can use the still free term "Glossiness" for the whole complete effect/final render...while in the Specular workflow "web section" is a lot of missunderstanding ... this might be one of the reason why most say that the MR workflow is more easy....
In that case I'd strongly assume that something has borked your Visual C++ installation in the past, if you don't also have updated your graphics drivers along with DS 4.9. Some 3rd party software can do things like that when deinstalling them. All dll's for the various DS versions are stored within the respective DS installation directory. The only things that are installed in a general directory are the Visual C++ libraries.
Well, on the PBR Metal we have Weight (strength/intensity of the BRDF layer), Reflectivity (simplified subsurface scattering effect for dielectric translucent materials), Roughness (simulated microfacet surface irregularities) and the Refraction Index to simulate the Fresnel effect. On the Top Coat we also have a "Custom Curve" layering mode to manually determine F(0°) and F(90°) and exponent parameters. Along plain values we also have the ability to use texture maps. That's IMO a pretty bunch of controls at our hands.
I took a look at the shader mixer composition of the shader in PBR Spec mode (eleminated all the other bricks not connected to the glossiness portion to ease the view). The "Glossiness" user parameter is connected to the "Map" brick which handels the texture image map. From there it goes into a "Gloss to Rough" brick (I assume that's the place where the "Inversion" takes place) and further into the Material brick ("PBR Specular Base") where it is connected to a "Glossy Roughness" parameter(!). That's the point where I got a "Yoda vision": >>There's no passion, just peace... there's no Glossiness, just Glossy Roughness<<.
In contrary to PBR Metal there's no "Square Roughness" brick connected to PBR Specular's Map or "to Rough" brick. Would we need one there, and if we don't: why?!? The "Glossy Specular" handels F(0°), what takes care for F(90°)? (Since the "Refraction Index" parameter is out of order there.) [WE REALLY NEED A DECENT SHADER MIXER HANDBOOK HERE!] With a proper explanation what a brick is for, and what it does and what it does not.
Arghhh, ninja'd again. Stop editing your posts, while somebody works on an answer...
Szark is right, even NVIDIA uses only the term "roughness" in MDL. And hidden away into the voids of the Shader Mixer, DAZ does, too.
UPDATE: due to some FUBAR from the one (two or three) that forged the Iray Uber the "Refraction Index" slider on the "Base" doesn't work; it seems it is set fixed to a value of 1.5 there.
yes i installed and deinstalled many different 3d and texture software trials over the last weeks... and the beta updated also Visual C++ .
Yeah...even the best we had in the past wasn't complete...and now with Iray and 3DL being in SM, it's definitely not enough.
that is an undestatement, how many of us have been asking for a manual and for how many years. I don't get pissed off that much but this sure gets my goat.
I think I'm more confused now about how to get good Iray skin shaders going than I was before I started reading this thread. I could really use a summary of what's working for people and what isn't.
@Gr00vus
everything what was posted about skin and setting up the uber shader DOES work
ok - i try again...setting: light - dome.. blue standard - infinte with ground
?...
left marble - base color black - PBR metalicity - zero reflectivity - roughness 0.5 - IOR changes nothing there it is now set to 1...weight 1
right marble - base color black - PBR specualr - specular color: zero, aka black - glossiness 0.5 - weight 1
PBR specular looks right to me - PBR Metalicity - looks like metal - way to much fresnel for the settings .... metalicity is on zero just saying...
for me it looks as PBR metal does not react on IOR or specular.and/or PBR specular has more roughness (should be the same!).(can somebody confirm this and replicate my settings - i want now be sure that i get the same renders as you do
and here with .5 roughness 0.5 reflectivity refraction 1.5 / glossiness 0.5 specular color 0.04 - both weight 1...
the difference is extrem - they should look the same... and Arnold is right, repclicated his marbles here in another light setting - PBR spec looks to rough for the values.
Wht drives me MAD is:
? we dont have PBR just since yesterday!
Convertion PBR MR to SG and vice versa!
Why is there not ONE single document to find in the web which explains this process with a COMPLETE material?
Does actually somebody know it ?
Is maybe here somebody which really knows how to do this - or learned it over the last months ? Arnold ?
a simple example....
a snowish material...in SG in MR
Base color : 0.54 0.54 0.43 same ? metalicity ON because the specular color is in the metal range?
Specular color: 243 /243 /243 reflectivity ?
Glossiness: 0.7 roughness 0.3
Can somebody POINT me on a document which explains this BASIC stuff ? whitout drifting in fresnel/lambert suqared and disney roughness and Mio of other formulas which i really dont want to know ?
I will code a SIMPLE online converter if there is really NOT one yet somehwere in the web. That can not be so difficult to explain and show.
the mix between Material infos with IOR (reflection) and IOR (refraction) whitout any HINT which one is meant.. no data for Roughness - color pickers whitout color space infos.. is the next part which drives me crazy (in the web)
i also read that the formula for reflectivity:
Reflection/Spec Amount % = ( ((1-IOR)/(1+IOR)) ^2 ) * 100
only works for non metallic materials...
for metals this formula should be used
Reflection/Spec Amount % = ( 1 - (4*Nd / ((Nd + 1)^2 + K ^2 )) ) * 100
i figured out that Nd is the IOR ( i think ).. i dont have a clue what K is
to get the IOR from a specular color.. which is needed too to convert..
IOR = (sqrt(Ks)+1)/(1-sqrt(Ks)) .... this is the only formula i have yet...
not clear to me is Ks... Ks should be the color i think.. BUT what kind of value? sRGB? Linear? wavelenght ? ... and this works only for grey specular colors.. right ?
Well, this link has been posted before, although it is worth reading, I think it is too technical to the average Joe or plain Jane. Here's what I know:
In Iray, there are two main characters, light and materials. Every material has to properly define how light interact at the surface and if this is a volume has to define how light behaves inside the volume.
You can define your material using MDL language or by using the properties on the Surface pane. Defining a material using the Surface pane you have three bases to choose from:
The "easiest" to work with is the PBR Metallicity/Rougness one. The PBR Specular/Glossiness is a little bit more complex but provides the better control in defining materials. The third one, Weighted base mixing is the most complex and provides the best control. These three degrees of control require distinct foundations(at MDL level) and therefore you can't go from one to the other.
You can see how different they behave if you compare two spheres one with MG and the other with SG and only varying the Diffuse Roughness. So, trying to define a Skin material using MR is plausible but you'll get more realistic results using SG. IMHPO, the best skin textures are the ones that were intended to 3DL.
Another thing to consider is keep things simple or you'll be missing the fun.
@jag11 thanks....
...
..
But this document does absolutly not answer how to convert different datas from different models ... i can easy do a material in specular and i can do also materials in metalictiy )having all the needed values ready from somehwere)....
But exactly this knowledge discrepance between Shader coders and simple user - like pointing on such a handbook MDL ( i dont mean you :-) is the problem in all PBR forums...
The average Joe decides to set up a material - > he searches in the web... and find a IOR list...
AND NOW? (i know a lot of that part yet).... but it toke me WEEKS! Months ! .. heck
he MUST known some formulas to set up a material.. but he ends in shader coders manuals instead on a simple how to do it document
Again . my example question above should be really simple... PBR is made to make things SIMPLE they say
a - one Material convertion :-)....
Who knows how to do it ?
i have a material in a shader with a spec color - with just some paramaeters- now i want it vice versa...
Well, K should be the color at normal incidence, and it desn't matter which color space it is, but linear is the recommended one. Works for grey specular color and the three seperate rgb channels.
@jag11
thanks for joining in
,,, i also think i figured out that it is NOT possible to copy a material 100% from SG to MR and vice versa.. but the results should be very close!
so... the above formula..
IOR = (sqrt(Ks)+1)/(1-sqrt(Ks))
while it makes sense to me using a linear GREY value in this formula.....
KS = 0.25
how would i do it with a specular Color ? where i have 3 values? aka 0.25, 0.22, 0.10....
The long way would obviously be that you could perform the function on each color value individually, then average the results of the three inputs to derive a final value. I'm sure there's a more elegant way to do so, I suspect in time someone will offer an equation that handles all three spaces at the same time.
@Rashad Carter thank you too for joining ... my goal is to have the 3 or 4 needed formulas -> working in excel sheet (google doc) or better online.. with the needed basic informations how to use such values without actually need to search or understand formulas (back to the fun).. so -while hijacking the skin thread.. (sorry @Gr00vus ).... i hope to have this together soon... for everybody.
Take your time. Until I upgrade my graphics card I'm not doing a whole lot of complex surface renders anyway. If/when you do get it figured out, you should contemplate making a product or products that make it easy for the rest of us to get good results.
I keep thinking I've got a result I like, then I move to a different light setup and it's time to start over.
@Gr00vus
well - dont hesistate to post some skinrenders - also the bad ones.... it is still the iray skin fiddeling thread
....
Clear to me is.... BETA 4.9 improves skinrenders - the redish problem is gone... even hairs look better...
Just one note -> i always said that i use HIGHER Glosiness values for my skin models then what is usally recommended... this migh result in problems with to much fresnel ambient reflections.... you can see this when you have partial .. as a example.. suddenly a colored face if your model is somehwere in the grass - or blue from the sky on the shoulder...
if this is your mainproblem.. then not your skin shader settings are bad.. you will need to mask glossiness in PBR specular to get rid of those reflections while still having the needed glossiness on oily areas such as the nose.
Still running some tests, too. For some whacko reason the "Refraction Index" on "Base", "Glossy" does nuthing... null, niente, nada.
On PBR Metal, only "Glossy Reflectivity" and "Glossy Roughness" work, on PBR Specular only "Glossy Specular" and "Glossiness". (PBR Metal's "Base" works in the same fashion as Top Coat in Reflectivity "Layering Mode". No "Refraction Index"/"IOR" parameter there). Determining specular reflection by index of refraction on PBR Metal just using the "Base" therefore is (Mission
) IMPOSSIBLE. 
But it is still working for PBR Specular, since the correct value for "Glossy Specular" is the result of the Fresnel Equation for F(0°). The value for F(90°) looks like to be fixed at 1.00 here, though.
On the Top Coat, in Fresnel "Layering Mode", IOR works on both mixes. "Top Coat Color" is the same as "Glossy Color" on the "Base".
The "Refraction Index" parameter at "Base", "Glossy" on the Iray Uber is like this picture:
And yes, PBR Specular looks too rough, clearly articulated reflections only appear at the final 1/100th from 0.9 on. Looks like a "Roughness Squared" brick is missing in PBR Specular's layout.