I tried rendering in two layers (backgorund and foreground) for
post-processing reasons (blurring background). For the foreground I used the
command line switch +ua +fn to enable transparency output to PNG. But the
result was not as expected. Only rays that directly hit the background plane
were transparent and there are problems with CSG. Reflected rays or those
going through semi-transparent objects produced an opaque alpha.
In BMRT  the transparency corresponds to how much of the background plane is
shining through or being reflected or whatever. Is there a way to achieve
this in POV-Ray?

Roy

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