Weird backplate image problem

[tricky]

My scene is getting rather complex, and I cannot seem to figure why I am getting the dark square patch overlaid on the attached partial render. It seems only/mainly to be affecting the two sofas but I cannot find what the problem is.

I am using a VrayPhysicalCamera with clipping planes as this view is impossible without cutting through the wall.



The dark areas seem to align with the backplate image which is here:-



This is a simple bitmap, set to environment and 'screen' coordinates. The RGB level of it is set to 20 so that it looks about right through the vraycamera.

The sofa is quite straightforward: just a fabric bitmap applied within a Color Correction map. No reflections or falloff.

Here are the settings for the Vray Environment:


Not sure what I need to do!

[tricky]

It seems to have something to do with multiplying the bitmap that I have in the environment slot. Why should this be giving me a problem?

If I set either Output Amount or RGB Level to 20, I get the problem. If I return to their default values of '1', the problem goes away, but then the background isn't bright enough.

Any suggestions?

[tricky]

It seems that the higher I go with my Irradiance map and Lightcache settings, the worse the problem becomes!

What on aarth is going on? Why do these problems always surface close to a deadline?

[tricky]

SOLVED!

The vraycamera was clipping through the walls. This meant that light from the multiplied screen-mapped environment image was adding light to the scene through the 'hole' that the clipping was creating. This also explains why the higher the quality of the solution, the more pronounced, or 'sharper' the effect!

I simply put a huge lump of geometry behind the camera to block out this additional lighting.

You live and learn...

[gfa2]

One man conversation....gotta love it. Nice to know the solution to the problem.

[tricky]

I know! How sad am I???

[vlado]

You could also have used a different color/map for GI and reflections, so that the background plate is used just for the background, but not for other calculations.

Best regards,
Vlado