PBR Material Question

[DCHA34]

I have downloaded a demo material which contains the following files which I have placed as follows with the Transfer Function parameter:
- diffuse --> Diffuse Color sRGB/sRGB Primaries
- reflection --> Reflection Color None/Raw
- glossiness --> Reflection Glossiness None/Raw
- normal --> Bump Normal Map None/Raw
- height --> Displacement Normal Displacement None/Raw
- metallic --> I don't use it

In this configuration, and this is how it is explained on the various tutorials I've read from all over about creating PBR material, my material is perfect and looks exactly like the preview that comes with the material.

But, when I took a closer look at the Cosmos library's material configuration, I noticed that the Transfer Function setting in the Reflection Color slot was set to sRGB/sRGB Primaries.

If, in MY material, I change Reflection Color None/Raw to sRGB/sRGB Primaries, then my material no longer matches the preview that comes with the material and looks "fake".

What is the real logic of creating PBR materials with V-Ray 6 for Sketchup when you download textures from the internet?

[jrozansky]

Yes is there a vid on this from Chaos?

[DCHA34]

Hello to all,
I just found a video on Poliigon's website about how to use their different maps with V-Ray for Sketchup.

You can see on this video that they use the reflection map with sRGB/sRGB but they reverse the texture in the color corrections. I just did a test, if I do that, it's the same visually as not using the reflection map.

But it is also written in their article entitled "What are the different texture maps for?" that "This map (reflection map) is only used in non-PBR specular workflows" So why use it in Cosmos materials?

I am completely lost...

[konstantin_chaos]

Hi DCHA34,

Bitmap / RGB Primaries:
First of all, the RGB Primaries setting doesn't matter if you have not enabled ACEScg in the global settings.
If you are using ACEScg the the RGB Primaries option of all 8bit textures should be set to sRGB and for 16 or 32 bit maps to Raw.

Bitmap / Transfer Function:
1) For all 8bit (jpg, png) color textures (diffuse, albedo, etc.) you should set the Transfer Function to sRGB.
This option ensures that V-Ray linearizes the map while rendering the image and then the sRGB gamma curve is re-applied in the VFB.
2) For 8bit textures that are used in float material slots (slots with numbers) you should set the Transfer Function to None.
Note that this also depends on how the textures were meant to be used but None is the most common configuration.
It is basically telling V-Ray that a color value of 0.5 in the sRGB image should be treated as 0.5 when rendering (without linearization).
If for example you want an area to be 50% reflective, you'd paint a 50% gray color in Photoshop and then assign the map to the Reflection slot of the material.
3) Normal maps should always use Transfer Function > None.

But, when I took a closer look at the Cosmos library's material configuration, I noticed that the Transfer Function setting in the Reflection Color slot was set to sRGB/sRGB Primaries.

This is OK as long as you're eyeballing the material.
Setting the transfer function to sRGB is just making the map darker by applying the sRGB curve to it.

If, in MY material, I change Reflection Color None/Raw to sRGB/sRGB Primaries, then my material no longer matches the preview that comes with the material and looks "fake".

This just means that the textures you've downloaded are meant to be used as is, without being linearized.

What is the real logic of creating PBR materials with V-Ray 6 for Sketchup when you download textures from the internet?

As I mentioned it depends on the texture but the rules I suggested earlier will in most cases give you the best results.

You can see on this video that they use the reflection map with sRGB/sRGB but they reverse the texture in the color corrections. I just did a test, if I do that, it's the same visually as not using the reflection map.

Can you share this video so that I can double-check.
Inverting the texture might be needed depending on what they've provided...
Using an sRGB transfer function might be a mistake in their video.

But it is also written in their article entitled "What are the different texture maps for?" that "This map (reflection map) is only used in non-PBR specular workflows" So why use it in Cosmos materials?

PBR means Physically Based Rendering.
V-Ray materials using the "Specular workflow" are also physically based.
That is why I do not agree with this statement all together.
If you prefer to use Metalness and Roughness you can.
We have used the classical V-Ray approach for most Cosmos materials which is also perfectly fine.

Another thing I want to note is that the first ever universal physically based material was introduced in V-Ray for 3ds Max back in the day - the VRayMtl (also known back then as the V-Ray Power Shader).
Later other rendering engines incorporated similar shaders.
Eventually game engines started doing the same and that is when the term PBR became popular.
One of the reasons why the Metalness / Roughness material model was adopted by more game engines is - it lets you define a material using less texture maps, a great benefit for such engines.
This doesn't make the Specular material model worse.
Using one or the other is a personal preference and V-Ray 6 supports all options.
For more information you can read the following article - https://www.chaos.com/blog/understanding-metalness

Regards,
Konstantin

[DCHA34]

Thank you for this detailed explanation.

[henriqueb]

Hello, DCHA34

You can see on this video that they use the reflection map with sRGB/sRGB but they reverse the texture in the color corrections. I just did a test, if I do that, it's the same visually as not using the reflection map.

I've been studying PBR materials since 2016 and it's important to say that PBR is a very practical method of creating materials. In general, we should think that the reflection color represents the maximum reflectivity of the material, so we don't need to use reflection or specular texture in this slot, just the color 100% white.

Poliigon textures work for different renderers and because of that it has different textures, you don't need to use all of them.

If the language is not a problem for you (I'm from Brazil) I recommend this class I took on my channel, converting V-Ray materials into PBR Materials: https://youtu.be/7-S1sJThbw4


Best regards
Henrique Barros

[DCHA34]

Hi Enrique,
I know your videos (I'm a former subscriber), I learned a lot from your videos.
That's why I'm asking all these questions about the "real" method (if there is one) of creating PBR materials.
You explain that you have to leave the reflection color at 100% white, ok, but then why Cosmos materials (for example) are created with a texture in this slot?
I was hoping to find a logic for creating materials, but I think that only the result is important, no matter the method.