Issue with uvwrandomizer + stoastic tiling when used in mix, composite and comptex maps via Vray normal map

[rita_sobral]

Hello,

When you are using either a mix, composite or comptex map plugged into a Vray Normal Map and you have one bitmap that is using a uvwrandomizer map + stoastic tiling and another bitmap with a different tiling amount with no uvwrandomzier then you get checkerboarding on your output. This is not true for Vray GPU or CPU

If you turn off stohastic tiling on the bitmap which has the uvzrandomizer then this disappears.

In my use case I am combining different normal maps for a large surface one of those is a 1:1 bitmap without a uvwrandomizer and the other one needs a uvwrandomizer + stohastic tiling and a larger tiling distribution.

Please see scene here which showcases this > https://we.tl/t-McS2ZA7xwk

[Alexander.Atanasov]

Hi rita_sobral,

Sorry for the late reply. Thank you for reporting it. I have logged the issue in our system under LAV-1826. Unfortunately I cannot provide an ETA on them but keep an eye out in the Announcement section of the forum where we post when new builds are available with their changelogs.

Best regards,
Alexander

[rita_sobral]

Thanks Alexander.Atanasov although I've just discovered this is actually a much more common issue regarding just stohastic tiling with normal maps. See attached images, this is a basic grass texture from cosmos which comes with UVWrandomizer + stohastic tiling out the box and presents checkerboarding


EDIT - see video when rotating sun and normals are all wrong - https://streamable.com/elivc1

[vladimir.nedev]

Thanks Alexander.Atanasov although I've just discovered this is actually a much more common issue regarding just stohastic tiling with normal maps. See attached images, this is a basic grass texture from cosmos which comes with UVWrandomizer + stohastic tiling out the box and presents checkerboarding


EDIT - see video when rotating sun and normals are all wrong - https://streamable.com/elivc1

I tried this material from Cosmos and I am not able to reproduce any checkerboard artifacts.

Can you provide a complete scene ?

Greetings,
Vladimir Nedev

[vladimir.nedev]

About the original scene - after you multiply the two normal maps with the mix, composite or comptex map, Vantage has to transform the resulting vector from tangent to world space.
This is done by using the uv transform of the UVW randomizer, which randomly rotates the space for each 50x50 tile.
So your additional normal map ICELANDLUMPS_Normal Map_0_0.png gets rotated differently for each 50x50 tile and you see this as the checkerboard pattern.

It's not something that can be fixed unless we add support for multiple VrayBumpMtls in Vantage.

Why the result is different in V-Ray - the mix, composite or comptex map will "hide" the UVWRandomizer, so V-Ray no longer uses it to transform from tangent to world space.
So you don't see the checkerboard artifacts, but the normals from tbxkajlk_8K_Normal.jpg are no longer correct.
You can't easily see it with that particular normal map, but if you replace it with something simpler like a bubbles normal map, it's obvious.

Greetings,
Vladimir Nedev

[vladimir.nedev]

Thanks Alexander.Atanasov although I've just discovered this is actually a much more common issue regarding just stohastic tiling with normal maps. See attached images, this is a basic grass texture from cosmos which comes with UVWrandomizer + stohastic tiling out the box and presents checkerboarding
EDIT - see video when rotating sun and normals are all wrong - https://streamable.com/elivc1

Ok, I was able to reproduce this, I just had to add some tiling to the uvw generator in the UVWRandomizer.

The issue seems to be happening in V-Ray as well, so it's not specific to Vantage.
Also it's a separate issue from the mix/composite/comptex one.

My guess is that the normal map in this case has some sort of "dominant" direction where the majority of the normals point to.
When you randomly rotate the whole map for each stochastic tile, this "dominant" direction gets oriented differently,
which results in different ratio of light to shadow for the tile as a whole, so each tile has a different overall "brightness".

Greetings,
Vladimir Nedev

[rita_sobral]

Ok, I was able to reproduce this, I just had to add some tiling to the uvw generator in the UVWRandomizer.

The issue seems to be happening in V-Ray as well, so it's not specific to Vantage.
Also it's a separate issue from the mix/composite/comptex one.

My guess is that the normal map in this case has some sort of "dominant" direction where the majority of the normals point to.
When you randomly rotate the whole map for each stochastic tile, this "dominant" direction gets oriented differently,
which results in different ratio of light to shadow for the tile as a whole, so each tile has a different overall "brightness".

Greetings,
Vladimir Nedev

vladimir.nedev I struggle to reproduce it in Vray GPU even with different sun position and exposure, I certainly can't make it look like Vantage with very distinct bright and darker tiles with hard edges Maybe Vray GPU hides it better.

It does mean I have to refrain from using Stohastic tiling on textures with normal maps as they often appear to give me very obvious checkerboarding which is unfortunate

[vladimir.nedev]

vladimir.nedev I struggle to reproduce it in Vray GPU even with different sun position and exposure, I certainly can't make it look like Vantage with very distinct bright and darker tiles with hard edges Maybe Vray GPU hides it better.

It does mean I have to refrain from using Stohastic tiling on textures with normal maps as they often appear to give me very obvious checkerboarding which is unfortunate

Yes, the problem is worse in Vantage and it's related to "dynamic textures".
You can try disabling the dynamic textures and see if that helps.
I will try to fix this particular aspect of the issue for the next release.

Attaching a sample scene where you can see the tiles in V-Ray CPU/GPU.

Greetings,
Vladimir Nedev