Vray Bitmap and UV planar mapped edges

[japetus]

I am new to using VRayBitmap, so bear with me...for my example I have a planar mapped box. The expect behavior with a regular Bitmap map is that the map will smear down the sides of the edges. However with a VRayBitmap the sides are just...gray? It's very odd. How do I get it to smear down the sides like is normal behavior for mapped objects? My "solve" so far has been to unwrap more, or scale faces like on this cube slightly so that the perpendicular faces to the planar map have a little width, then it seems to work ok. Am I doing something wrong? I'm on 3ds Max 2021.3.2 , Vray 5 update 1.3.

[japetus]

Another example of VRayBitmap vs regular Bitmap

[tashko.zashev]

Hi,

Yes, there seems to be a difference in how the mapping works in this specific setup. I believe that the V-Ray Bitmap behavior is the right one and produces a more accurate result.
Do you find the Bitmap result useful in any specific situation?

[Morne]

I'd disagree and say bitmap seems correct. We also use bitmap for effects like that, very often

[fixeighted]

Weirdly, I can get this to work just fine, though only when switching to elliptical or isotropic filtering.
Hopefully that works similarly for you all

[Vizioen]

Con confirm this has something to do with filtering. Elleptical and isotropic still have this behaviour.

[japetus]

I'd agree that the default behavior is not what I would ever want to have happen...but changing the Filtering to Isotropic solved the problem! Elliptical was better than default, but still weird, Isotropic worked best for me. Thanks guys for the help. Was pulling my hair out yesterday! Been trying to convert some old projects to ACES which I have also been learning, so had to track it down for a while.

[^Lele^]

Isotropic has kernels and kernel sizes closer to the standard Max bitmap loader.
The other two modes will allow for much better detail retention, but come with caveats (notice with IPR also elliptical starts noisy around the edges, but eventually cleans up.).
Setting the bitmap to the simplest bilinear interpolation fixes the issue for Sharp Isotropic too.

[japetus]

My big question though, is where does the edge color even come from? Why is it gray? it seems somewhat related to the map, but in another test I did was pulling color from some other area of the map no where near the UV coordinates.

[^Lele^]

It could be a bug, indeed, but it could just be the way the sharp kernel works.
Gray being a default color when it finds no bitmap data within the kernel footprint.
Devs are reading this, though, we'll know soon enough if they can find better ways about this.

[japetus]

Great, thanks for the fast replies. The filtering solution works well in the meantime...

[^Lele^]

So it looks that this is what it is.

Please use one of the other filtering methods for this kind of scenarios.