I’ve seen mention of this on a few other threads, but not an actual solution.
I’ve seen that a bitmap or colored env. background will be okay with a physical camera if you uncheck Affect BG in Color Mapping.
However, if you make an object Matte with a -1 alpha, vray renders the matte object as a “color mapped” version of the background rather than ignoring the ignoring color mapping as it does with any directly visible portions of the background plate.
In other words, a bitmap env. background will be black when viewed “through” a matte object (with a physical camera -- with affect BG unchecked) unless you go into the bitmap and CRANK up the RGB level or Output amounts. This will blowout the main background, but the matte will now start to look like something that is not black.
Bottom line, the background can be isolated from physical camera’s color mapping (exposure, I suppose) but the matte objects don’t respect that.
This isn’t a problem for comping since a proper alpha is generated by mattes, but it is a problem for previewing.