Author Topic: physical mat | reflection intensity question  (Read 3084 times)

2022-01-21, 13:32:22

Stefan-L

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dear all,

sorry for my maybe obvious question, but the more i work with the new physical materials,
the more i start to lack a direct control on the reflection intensity (other than lowering or raising the ior). 
mostly to lower the reflections a bit as i see in in real world products i need to recreate.

to all my understanding the IOR is MAINLY defining the falloff/fresnel curve of an material, not only the intensity of the reflection, so metals have a very different fall off curve than water which again is different to glass and so on ( as easy seen on https://refractiveindex.info/ ).

but atm i see no other way to tune the reflection intensity in the physical material, other than changing (raising or lowering ) the IOR value.
- do i oversee something important?
- is this really physical correct?
- aren't there materials in reality who have a certain fall of curve , like glass, but different reflection intensities? (lower than pure ior value would indicate p.e.)
- would it maybe be needed, to have an intensity slider i % or a value (ideally with texture slot) for the reflection, at least to lower it at least for artistic reasons i think this is important.

as example: seeing at real world glass products i think also reflection can very different for different products, and i assume they all have an ior of 1.5-1.6, not much lower.
so i feel a physical material still needs some way to set the reflection intensity independent from the fall off curve (ior)

what does the corona team or other users think on that?

maybe a "level" setting like in Volume tab,
or amount with a texture slot, like in refraction tab of the new physical mat would do it?

cheers
Stefan

p.s.: just to make clear i love the new Physical material,and the intention behind it. all i post is only trying to help to improve it:)
« Last Edit: 2022-01-22, 23:16:40 by Stefan-L »

2022-01-21, 13:56:39
Reply #1

ingemar

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I’ve been wondering the same thing, missing a slider in some cases. But I’ve also experimented with micro-imperfections in various channels to lower reflectivity. Is a reflection strength slider perhaps just a cheat to simulate imperfect surfaces?

2022-01-21, 14:51:51
Reply #2

aler

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sorry for my maybe obvious question, but the more i work with the new physical materials,
the more i start to lack a direct control on the reflection intensity (other than lowering or raising the ior)...
I agree with everything said, because I too feel this limitation.
Physical Material is good, but it seems that the developers have overdone it, too limited the possibilities of users.

2022-01-21, 16:03:09
Reply #3

Stefan-L

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"Is a reflection strength slider perhaps just a cheat to simulate imperfect surfaces"

+1

2022-01-21, 17:41:20
Reply #4

burnin

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Refl. Intensity & IOR are basically same thing.

Imperfections are "simulated" using roughness.Which is what makes material surface IRL appear diffused, rough, scratched, less smooth (less glossy) but reflection intensity stays same.

Do you have any specific situation/case in mind?
« Last Edit: 2022-01-21, 17:46:22 by burnin »

2022-01-21, 18:24:04
Reply #5

Stefan-L

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well, i am not totally sure, but that's another thing.

i do not mean slight imperfections, but the pure intensity itself often needs to be reduced.
like there are glasses in reality with greatly reduced reflections but still an refraction like glass (around 1.4-1.6), probably with some special coatings  that absorb reflection, etc and our archviz customers very very often demand less reflections materials, like glass,

so at least for artistic reasons it might be very good to be able to mimic these materials which do exist in reality, or to react easy on customer wishes without "destroying" the rest of the material (like in setting the ior way too low, or need to change the roughness, which the end customer probably also not wishes).
so i not want to set the glass ior to like 1.1 (which will give me a wrong refection look) but be able to reduce the reflection intensity by 50% as example.

or another example i just work on which is more about work flow: a floor with different tiles(differences in material of the tiles), that i want to have slightly different reflection intensities, i can set variations in all material features only not in reflection. this makes me feel  limited. i needed to make several separate materials and assign them manually. this is a bad work flow and costs time. this would lead to the need for a value+texture slot as it is in refraction too.

i believe such features like the physical should make our live easier, almost all other phymat features have a "value+ texture " setting, so i hope this could be added to the reflection too. it is not more or less non-physcial than the volume or refraction setting i believe.
« Last Edit: 2022-01-21, 18:31:26 by Stefan-L »

2022-01-21, 19:52:01
Reply #6

aler

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i believe such features like the physical should make our live easier, almost all other physmat features have a "value + texture " setting, so i hope this could be added to the reflection too. it is not more or less non-physcial than the volume or refraction setting i believe.
+1

2022-01-28, 13:32:02
Reply #7

Stefan-L

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here is one example of real world materials that seem not possible to create with the new physical material unless it gets some kind  of "dim reflection" feature:

https://uk.saint-gobain-building-glass.com/en-gb/sgg-vision-lite

Staint Gobain is one main glass producer worldwide, the glass is widely used in architecture. one big feature it has is low reflection glass. see the table on that page how extreme the reflection is reduced while retaining transmission(and glass like IOR refraction like around 1.5).
lass materials are today one essential thing for architecture, but the above materials are only one example, but in architecture are several real word mats, like facade panels that have intentionally reduced reflections.

while for opaque materials it might be a way to reduce the ior to dim reflections,
for transmissive materials that need to keep a correct IOR (glass = 1.5), one atm cannot reduce the ior while setting the correct physical real word reflection.
so i hope for a intensity or value % slot as we have it in other material features already in the new physical material.

i only try to improve the phymat to be able to really be capable to cover most of the real world materials, so we can fully switch to the new, otherwise great(love it!), new physical material :-)
« Last Edit: 2022-01-28, 13:44:44 by Stefan-L »

2022-01-29, 09:22:54
Reply #8

aler

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Dear developers, it is strange that you still did not answer in this thread.
Then I will support Stefan again and give an example.
A simple rough metal (for example Aluminium), but its specular is overexposed. It's Clamping, loss of color, and that's bad. And inside the material I do not find options to adjust the specular the way I need it (pic.1).
But I would like the metal to have a soft specular (pic.2). Here in VFB in Tone Mapping I have raised Highlight Compress to 20. However this is not the best way, because everything else has also become pale.
Of course you can do it through Multi-Pass: assign a separate mask for metal, and then from 1 render make 2 saves - the first is normal, the second with a weakening of the overexposed, and then work in Photoshop (pic.3). This is a working method, but it involves additional actions.
Therefore, it would be more convenient if for Specular/Reflection were provided for convenience additional adjustments (Level, Color, Mix Strength...) (pic.4).
« Last Edit: 2022-01-30, 03:00:20 by aler »

2022-01-29, 13:19:38
Reply #9

burnin

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Hard to conclude anything... as it appears to me, simply darkening base color could do... Care to provide scene?

-------------------------------

For the Saint-Gobain glass you can study/check & see how it's done w/ Indigo renderer since original producer has provided their official materials (w/ measured tabulated data) HERE.

Notes:
Quote
Official measured glass materials from Saint-Gobain
Post  by saint-gobain-glass » 24 Aug 2011 09:28
Dear Indigo users,
 Please find in the material database several new materials, officially measured, provided and supported by Saint-Gobain Glass, a glass making company.
 
 These materials are not licensed under the creative commons license, but under a specific copyright license included in the material description and in the igm code. To summarize, the materials are free of use for any commercial and non-commercial project, and sets no restriction on the use of the generated images. Free distribution of unmodified material files associated with brand and products names is allowed. Main restriction is on modified versions of the materials which cannot be distributed.
 
 Best Regards,
 
 Etienne

Finally/TL;DR,
IME, lower IOR is defined, I think this way, because Indigo abides to the same physical principal & CG model(?):on a single material reflective = refractive IOR, which can't be separated, so when user wants to make this "duality" physically accurate, it has to model it. And here's where higher FP accuracy & volume priorities come to play. 
So, for those scientific & engineering minded, wanting to know more on predictive rendering for these kinds of complex materials, it's worth to tickle the brain in the Ocean ( ;) involved in creation of glass & engine).

2022-01-29, 15:07:15
Reply #10

Stefan-L

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"IME, lower IOR is defined, "

that does sadly NOT work, as the ior then would be needed to be like 1.07 in my scene case, which doesnt look like glass in its refraction anymore
.i tested that already.

the indigo render cases seem not to have any solution and seem also not covering the low reflective glasses that archiz very often  needs.
it is not only a but the one specific glass but there are many variants. also customers often demand " make the glass a  lot less reflective", where we  as renderer should to be able to suit their wishes.

we need a way to recreate this reflection reduced materials (that are real wordl materials, they still do have a refraction IOR of 1.5-1-6)

i think in reality the glass producers do this with some special coatings, but the corona coating not let me do this complex effects(reduce reflection but keep glass super transparent)

we DO have currently have a value % in the phymat to "dimming effects" already for:
1) base diffuse
2) refraction
3) volume
4) clear coat
5) translucency
6) thin absorbtion

ONLY not for normal reflection, i really ask myself WHY this single  one is missing?
the other % values arent more physical or less than they would be for reflection to all my understanding.
as it would only reduce reflections, the danger of making too bright unrealistic materials isnt the case in such a setting.

this is for every days use a very important thing to keep us artistic control and to mimic some important real world materials, as explained-
for refractive materials lowering IOR is not an option to achiev that wanted effect.

i do love the new material , beside this single missing control, which i truly believe is very important
« Last Edit: 2022-01-29, 15:21:35 by Stefan-L »

2022-01-30, 00:20:52
Reply #11

aler

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as it appears to me, simply darkening base color could do... Care to provide scene?
Then it will not be light Aluminium, but a dark metal. I attach the file, I hope you will show it as it should be?
...and also, if you switch the material from "Non-metal" to "Metal", then even the IOR becomes unavailable. How to regulate?

...to Moderator: maybe this topic should be moved to the "Feature Requests" section?
« Last Edit: 2022-01-30, 02:56:38 by aler »

2022-01-30, 12:31:20
Reply #12

piotrus3333

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Dear developers, it is strange that you still did not answer in this thread.
Then I will support Stefan again and give an example.
A simple rough metal (for example Aluminium), but its specular is overexposed. It's Clamping, loss of color, and that's bad. And inside the material I do not find options to adjust the specular the way I need it (pic.1).
But I would like the metal to have a soft specular (pic.2). Here in VFB in Tone Mapping I have raised Highlight Compress to 20. However this is not the best way, because everything else has also become pale.
Of course you can do it through Multi-Pass: assign a separate mask for metal, and then from 1 render make 2 saves - the first is normal, the second with a weakening of the overexposed, and then work in Photoshop (pic.3). This is a working method, but it involves additional actions.
Therefore, it would be more convenient if for Specular/Reflection were provided for convenience additional adjustments (Level, Color, Mix Strength...) (pic.4).

Highlight compression alone is not a full tone mapping solution. you need to add contrast. preferably with curves.
Marcin Piotrowski
youtube

2022-01-30, 12:44:44
Reply #13

Stefan-L

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thx, but we do not talk on high light compression or tone mapping;)

it is about simple be able to control (reduce) the reflection,
in special for refractive materials (other than lowering the IOR non-physically)

2022-01-30, 12:58:37
Reply #14

piotrus3333

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you are trying to create coated/layered material. CoronaPhysicalMtl is simply not what should be used for that purpose. use the legacy and/or layered mtl. CoronaPhysicalMtl is ment for simplyfing creation of basic, physically correct shaders.
Marcin Piotrowski
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