I think he means that sometimes they're opening the file specifically to re-render the small portion. So the VFB is blank by default as nothing has been rendered yet.
Yes, this. Occasionally a Client may send an updated map for fabric/rug/finish that they wish to use and that may be the only thing that needs rendering.
Open scene, change material, render object only. My original point was that it seems the noise calculation is thrown off by black pixels/empty space in the VFB but rendering a crop makes it more time consuming to comp (manual alignment instead of dropping a full image in place using the alpha)
Can you explain what you mean here?
If you use the "Clear VFB" option, this will reset the whole content of the VFB to black when you start rendering. If you disable it, it will show whatever was rendered previously.
Do you mean that you would like to load an existing CXR image into the VFB without starting the actual rendering, and then draw some regions to update some areas?
Loading a CXR (or other) into the frame buffer would also be really helpful for the purpose of region-ing the object you want prior to starting the render :)