Imposible to get real translucency on sinngle face models on the new Mtl

[adanmq]

Hi.

First of all thanks for all the great job you put inthe new release, i´m loving it so far.

I have a problem using the new translucency mode for Vray Mtl on Vray 5, Update 1. I understand why this new system it's better when I try to do real SSS on a model whith thiknes but now I can't recreate simple translucency anymore on models without thickness like leaves, grass, and so on. This is a huge problem for any scene where vegetation it´s involved.

Before the change the only way i found to do simple translucency using Vray on single side models was using 2Side Mtl to control the amount of translucency and Hybrid translucency on the Material to control the color of the translucency because using only 2Side it's not good at all, leaves have different albedo/translucency. I know probably this is not the original workflow intended for 2Side/Translucency but it works. I spent over a year scanning all kinds of vegetation and this method works very well, allowing me to get an almost perfect match compared to the scanned results. But now i can't reproduce anymore the real behavior on Vray using the new models i read the changelog and i didn't find any clue of a possible solution so i wonder if you have plans to create additional translucency models for single side objects otherwise i think it's a very important problem for anyone doing archViz or vegetation related renders. All other render engines on the market, including Corona are perfectly capable of doing this so i don´t know if i´m missing something. I will appreciate any help or clues in the right direction, as I told you we have been working on 3D Scanned plants for VRay and other render engines for more than one year and I will like to provide to my clients the same quality I get on the other engines and without translucency it's impossible. I think the old model should be available or replaced for a new translucency for single face objects.

Here you can see some examples I render on the old translucency and also a comparison with the new model. The image where only 2Side it's used looks like plastic and the scanned translucency cannot be used in any way. I can provide additional information if you need it. Thanks in advance!

[Alex_M]

Really? When I can, I always use VrayMtl's Hybrid translucency for vegetation with no thickness because it gives better results (to me at least) to using solely Vray2sidedMtl. Vray2sidedMtl without Hybrid translucency looks kind of unnatural to me. I don't mind that it's not "the physically correct way" if it gives appealing results. Can you please bring Hybrid translucency back?! Or maybe have a replacement that works similarly? The projects I do rely heavily on good looking vegetation. Does that mean that this is now harder to achieve with Vray 5.1?

[JonasNöll]

Hi,

I'm sorry, but can you please clarify what exactly you mean? I'm really interested in this issue as well but didn't quite understand what is your problem. Maybe it's my issue, English is also not my native language.

So you mean that before Update 1 you were using the "old" Translucency Workflow (HardWax,Liquid,Hybrid) in the VRayMtl on 1-sided polygons like leaves and got an effect that looks better and you can not reproduce with the VRay2SidedMtl workflow?

Huge fan of your tutorials btw, thx for those

[Moriah]

This is very true, we just updated yesterday and while old models with old shaders work fine, on the new one we don't have easy access to the hybrid model anymore... This is a huge issue for all types of vegetation.
Could you please at least give us access to the old models on the dropdown menu? Thank you

[^Lele^]

EDIT: nevermind.

[vlado]

The translucency modes, both the new and the old ones, were never intended to be used on thin single-surface geometry; if you used them for trees etc, you were probably slowing down the renderer quite a bit. The proper way to do this has always been the VRay2SidedMtl material.

With that said, in V-Ray 5.1 there is a hidden VRayMtl option called "refraction_thinWalled" which, when combined with the SSS translucency mode, will work on thin geometry quite well. In that case, the SSS color will be the backside color, and the SSS amount will control the translucency effect. This option will be officially exposed in Update 2.

I don't plan to expose the old models however; they are not physically accurate; between the new modes and the thin-walled refraction, there should be no need for the legacy modes anymore.

Best regards,
Vlado

[adanmq]

Hi. Thanks a lot for taking the time to respond to my post.


I understand that the Translucency was never intended to be uses for Single-surface geometry but it was the only way to get the effect looks like the real plants, 2Side only takes into account albedo from the other side and in the real world light coming from behind the leaves it's not like the albedo. I'm sure you already know this and can be measured in the real world. Other engines have this kind of simple translucency for years.


So when I use only 2Side Mtl the effects it´s not correct, does not match reality, and the plants look really bad, without life. Will be great if we can afford real thickness on the leaves and SSS to make forest using thousands of trees but I don't think the technology it's there yet. So we need to find biased ways of imitating the real behavior on Single side leaves.

I will love to try the Hidden material and if it simplifies the process i will be grateful to forget about the old and incorrect way of doing it. ¿There is a way of trying this material on the actual Update?

Thanks again for your time.

[vlado]

I understand that the Translucency was never intended to be uses for Single-surface geometry but it was the only way to get the effect looks like the real plants, 2Side only takes into account albedo from the other side and in the real world light coming from behind the leaves it's not like the albedo. I'm sure you already know this and can be measured in the real world.

I've measured it, and the VRay2SidedMtl material is correct I did a post here on the forum a while back, I should try and find it.

So when I use only 2Side Mtl the effects it´s not correct, does not match reality, and the plants look really bad, without life.

I've compared the VRayMtl result to lots of references and generally it looks correct. Arists often want to exaggerate the translucent effect because it looks nicer, but plants in real life tend to be darker.

I will love to try the Hidden material and if it simplifies the process i will be grateful to forget about the old and incorrect way of doing it. ¿There is a way of trying this material on the actual Update?

Put the VRayMtl material in the compact material editor in the first slot, and then open the MaxScript listener and type

meditmaterials[1].refraction_thinWalled=true

Here is a link to a video that shows it:

Best regards,
Vlado

[brunonz]

The translucency modes, both the new and the old ones, were never intended to be used on thin single-surface geometry; if you used them for trees etc, you were probably slowing down the renderer quite a bit. The proper way to do this has always been the VRay2SidedMtl material.

With that said, in V-Ray 5.1 there is a hidden VRayMtl option called "refraction_thinWalled" which, when combined with the SSS translucency mode, will work on thin geometry quite well. In that case, the SSS color will be the backside color, and the SSS amount will control the translucency effect. This option will be officially exposed in Update 2.

I don't plan to expose the old models however; they are not physically accurate; between the new modes and the thin-walled refraction, there should be no need for the legacy modes anymore.

Best regards,
Vlado

Hello Vlado,

So, what is the way to go to get those nice translucency on leafs that Adan has mentioned? This has become a standard workflow for many 3d models providers, including MaxTree that are included on Chaos Cosmos, and others like 3dcollective, Poliigon and etc.

To be constructive, i think you should have a temporary option to get the "old" workflow while you guys sort this "issue", since thousands of 3d plants will look different from now on.

Tks!

[vlado]

i think you should have a temporary option to get the "old" workflow while you guys sort this "issue", since thousands of 3d plants will look different from now on.

No, they won't look different. The old behavior is still there; if you load an existing asset it will work just fine and will render as before and you will still have access to the old parameters.

MaxTree that are included on Chaos Cosmos

We have reworked those assets for Cosmos.

Best regards,
Vlado

[Pixelcon]

Arists often want to exaggerate the translucent effect because it looks nicer, but plants in real life tend to be darker

It's this precise attitude that really frustrates a lot of users (imo) and is why a lot of people moved to Corona.

Artists are very often required to create things that do not follow the 'rules' of reality and taking away the tools, hacks, and loopholes that allow them to do so is just exasperating. Perhaps a tooltip that suggests the hacked setup is not physically accurate would satisfy both parties? Same with unlinking refl/spec glossiness...

[vlado]

It's this precise attitude that really frustrates a lot of users (imo) and is why a lot of people moved to Corona. Artists are very often required to create things that do not follow the 'rules' of reality and taking away the tools, hacks, and loopholes that allow them to do so is just exasperating. Perhaps a tooltip that suggests the hacked setup is not physically accurate would satisfy both parties? Same with unlinking refl/spec glossiness...

Well you can't unlink highlight and reflection glossiness in Corona either. You are right that artists may want many artistic effects and this is totally fine, that's why we are adding the new mode to VRayMtl, after all. I was replying to the statement that VRay2SidedMtl is not accurate.

Best regards,
Vlado

[brunonz]

It's this precise attitude that really frustrates a lot of users (imo) and is why a lot of people moved to Corona.

Artists are very often required to create things that do not follow the 'rules' of reality and taking away the tools, hacks, and loopholes that allow them to do so is just exasperating. Perhaps a tooltip that suggests the hacked setup is not physically accurate would satisfy both parties? Same with unlinking refl/spec glossiness...

We could explain to the client that real life is real life and we cannot do anything about it, lol.

[adanmq]

Hi!.

Sorry if i can't explain properly my point, english it's not my stronger skill.

I will try to elaborate.

I have set up a method to scan the leaves: Cross Polarization to capture the front and back side without reflections. Photometric stereo to capture NormalMaps AND uniform and very consistent light under the leaf to capture translucency. This setup allows me to capture 2 albedo maps (front and Back) 1 translucency map (I normalize the result to make sure the parts where i don't have leaves have exactly 1 in value on the EXR so the translucency texture represents how much light can go through the leaves. (I attach a small crop of the textures so you can see my starting point, i have the original 8K also)

Since I can't use the texture I capture on the 2Side Mtl I will get a % of the albedo on the other side and translucency it's completely different from albedo so this method doesn't look accurate at all i don´t want a dimmer version of my albedo as translucency i want my translucency texture. Maybe I can divide the albedo on top of the translucency and try it on the 2Side but it doesn't look intuitive at all and I never try it. So my problem is that Albedo and translucency are completely different in real life and using only 2side I can't replicate this behavior that's why we use the translucency on the Mtl itself to get different texture on translucency and not just dimmed alvedo.

I attach the textures here: https://we.tl/t-J7H9hmsADe and 2 examples one using only 2 sides and the other using the translucency texture previously scanned. Since I scanned translucency using an uniform light equivalent to 1 y recreate this on Vray, I put a rectangle light with intensity 1 really close to the leaves and the only result that matches reality it's the one using translucency.

The old and wrong method were the translucency map mixes perfectly with the albedo depending on how much light go through the leaves and the other one using only 2Side where the leaves looks plastique because we only get a % of the albedo and no translucency texture mixing. And this is using an HDR where there is light coming from every direction in real scenes where you put your plants on dark corners. 2Side looks really bad compared to the translucency one. I´m not looking for an exaggerated or artistic look on my plants. I want to make a perfect copy of the real plant as I can in 3D. That's why i´m not using my eyes to evaluate the result but measurements on the real world vs linear render results.

Maybe I'm missing something but I just can't get accurate materials using only 2 sides. Is there a way to introduce translucency textures scanned from the real world on the 2Side Mtl?. I will try the new material as soon as i can. Thanks again for your patience!

[vlado]

Thanks for the explanation, this is super interesting and quite similar to what I did in my tests. Do you think you can show the original photos too as well as your actual VRayMtl setup? I would like to see the physical set up of light and camera so that I can try and recreate it in 3D. It's quite possible that I'm wrong (I've been wrong many times before ) so I want to make sure that whatever we do to the material is ok. If the new option works well, then I will simply expose it in the UI so that you can use it instead of the old translucency modes.

Best regards,
Vlado