Made a search bud I didn’t find anything on the subject. Sorry if I’m wrong and litter.
I have some Blend materials and they use bitmaps as masks. They look horrible unless I use VrayBmpFilter. Problem is that Max don’t include this part of the material when collecting for Backburner. I know you are aware of the fact that maps located in the VrayBmpFilter don’t show up in the Bitmap/photometric paths. And that once you fixed that this issue might be resolved at the same time.
Workaround is simply to use a network path to those maps nested but when you have a few and as I work alot locally. It takes time.
