texture render difference CPU - GPU

[floris_drupsteen]

I always work in cpu rendering. But I ran into a problem I could not fix.
I need to render a specific fabric with fine dots. But this causes moire effects in cpu mode.
I tried all anti alias options and many other things. But could not fix it.
When I tried it in GPU rendering it does look good. (although lighting looks different. I think it has to do with object properties tag on some objects that doesn't seem to be supported).
Can you make the mapping in CPU mode the same as the mapping in GPU mode?

[shaio]

Hey floris_drupsteen,
can you please share the scene or the texture with me so I can take a look?

[floris_drupsteen]

Hi Shaio,
here's a link to the file with 3 different textures that all have this issue.
https://we.tl/t-wae5Hl1QNW
Textures are very big because I need those details.
thanks
Floris

[YunalZobu]

Something more or less looking like this? btw a bump texture was missing, idk if that's important or not.

[floris_drupsteen]

Hi YunalZobu,

that looks perfect.
Indeed, the bump map doesn't matter. I think it was set to 0
Question is if you did reach it using CPU or GPU?

thanks!
Floris

[YunalZobu]

Hi floris_drupsteen ,
left side is cpu and right side is a gpu render, both rendered to a similar noise threshold.

I changed the sampling for the diffuse texture to none, but there might also be another way to achieve this

[floris_drupsteen]

@YunalZobu
It certainly looks good. Can you share a screenshot or tell me where to find the diffuse texture sampling settings?
I looked but can't find it..

[YunalZobu]

@YunalZobu
Can you share a screenshot

Sure thing

[floris_drupsteen]

ah, yes of course. That has been there forever
Looks like the GPU uses the "none" sampling all the time.
Thank you!

[shaio]

Thank you for the scene floris_drupsteen. I'll try to figure out what is going on and see if there is a workaround for it, I'll let you know.
(ps: I just saw that Yunal answered you while I was writing the post)

When I tried it in GPU rendering it does look good. (although lighting looks different. I think it has to do with object properties tag on some objects that doesn't seem to be supported).

You have a difference between V-Ray and V-Ray GPU in the final rendering because you're using the "Diffuse Roughness" parameter set to 1 which is not supported by V-Ray GPU (this is shown in our supported features page as well).

I want to share some recommendations about your current setup for the Render Settings.
If you don't have any specific reason to use the settings shown in the screenshot below and if you're using them because you used to do this in V-Ray 3 then I'll strongly recommend using the default values especially for new scenes and most importantly for the Type and Mode dropdowns inside Color Mapping.



Another recommendation would be for the VRayFresnel that you're using inside the Self illumination.
I guess this is done, so you can have a falloff effect for the fabric (well known old technique). However, since this is emitting light it can cause some additional calculations that will occasionally slow down the render time in a different scenario since it needs to calculate all light bounces and will of course make the material physically inaccurate. My recommendation here is to use the specially designed "Sheen" parameters inside the V-Ray Material that will do this falloff for you based on the lighting of the scene.
Here are some examples that I made for you of the Falloff effect only so you can check the difference. The lower the Glossiness for the Sheen, the more Falloff you will have.

Example with Self-Illumination:



Example, with Sheen and Sheen Glossiness set to 0.85 :

[floris_drupsteen]

Hi Shaio,
thank you for your answer and your tips. I will surely make these changes to the setup.