Differences in bump / normal between Vantage and Vray GPU & CPU

[suzanne_doherty]

Is it just me, or is there a big difference between Vantage and Vray GPU / CPU?

I have a material that in Vantage needs the bump to be set to 100, but in GPU I need to lower this to around 25 for the same look.

Is this a glitch?

[vladimir_krastev]

Hi, thanks for posting.
There are small known differences between the bump in V-Ray CPU and V-Ray GPU that we are working to clear out.
Could you share a bit more details about your material? What nodes do you use?
If you can share a screengrab with the nodes this will be great.

[vladimir.nedev]

The normal map results should be pretty much the same between Vantage and V-Ray CPU/GPU,
unless you are blending the textures in unsupported ways, like if you are blending several different tangent spaces (different uvw rotation, scale, etc).

For bump mapping, Vantage won't match V-Ray CPU/GPU.
We do plan some improvements in the future, if you have a scene, please send it for future testing.

Greetings,
Vladimir Nedev

[suzanne_doherty]

vladimir_krastev The materials are very basic, just bitmaps loaded into the bump slot (see attached).

vladimir.nedev I will run a test with normal maps. No strange blending, just bitmaps in the usual slots.

See the comparison on this shot. The bumpy metal is most noticeable, but you can also see differences on the black plastic molded pattern.

[vladimir.nedev]

See the comparison on this shot. The bumpy metal is most noticeable, but you can also see differences on the black plastic molded pattern.

This kind of difference might be related to how the object is scaled (object vs world space), but I am not sure if it's that or something else.
Vantage and CPU look pretty close to me in this particular case.

Greetings,
Vladimir Nedev

[suzanne_doherty]

This kind of difference might be related to how the object is scaled (object vs world space), but I am not sure if it's that or something else.
Vantage and CPU look pretty close to me in this particular case.

Greetings,
Vladimir Nedev

Yup the GPU is odd one out here. The object scale is 100%, and just mapped with a box UVW Map.

[suzanne_doherty]

Here's the normal map test, and this is the one that I really noticed the difference. But as you can see in the 4th image, by turning down the bump intensity, it starts to look acceptable when compared to Vantage.

Edit - I should also add that this scene is lit with spotlights, using Area Shadows, which I didn't realise until this project that they're not supported by GPU, so it's harder to compare the GPU and Vantage renders as the GPU shot won't correctly show the spec highlights.

Edit 2 - I cant wait until you have some kind of render queue for Vantage, as this would remove the need to swap between Vantage, GPU and CPU for rendering.

[vladimir.nedev]

Here's the normal map test, and this is the one that I really noticed the difference. But as you can see in the 4th image, by turning down the bump intensity, it starts to look acceptable when compared to Vantage.

Here the normal map doesn't look normalized to me (there are some white areas).
Was it created by baking or by some other process ?
Maybe this is what causes the difference.
In Vantage we have an optimization that drops the blue channel for normal maps.
This way we can store the normal map in 2 bytes instead of 4 bytes per pixel (you can't have an 8-bit texture with exactly 3 channels, it's either 2 or 4).
I vaguely remember some potential issue with this optimization and non-normalized normal maps.
Edit: the mismatch might be caused because in Vantage we would normalize the normal map in order to drop the blue channel, while V-Ray will normalize it a later stage after applying the normal map amount.
I have to check, but I will need that scene.

Greetings,
Vladimir Nedev

[suzanne_doherty]

Here the normal map doesn't look normalized to me (there are some white areas).
Was it created by baking or by some other process ?
Maybe this is what causes the difference.
In Vantage we have an optimization that drops the blue channel for normal maps.
This way we can store the normal map in 2 bytes instead of 4 bytes per pixel (you can't have an 8-bit texture with exactly 3 channels, it's either 2 or 4).
I vaguely remember some potential issue with this optimization and non-normalized normal maps.
Edit: the mismatch might be caused because in Vantage we would normalize the normal map in order to drop the blue channel, while V-Ray will normalize it a later stage after applying the normal map amount.
I have to check, but I will need that scene.

Greetings,
Vladimir Nedev

Maybe it's not the best example to test normal maps, as this was adapted from another library (I've never really fully understood Vrays normal maps in truth), but it's interesting that by lowering the bump intensity on this and the metal material to 33% they look very close.