Yep, what diolma said, but there's one more VERY important ingredient;

If you want the pic to be "pure", you must also ensure that
Bryce's main ambient "feed" is also pure.

This is done by ensuring that "Ambient" in the sky controls
are set to "pure white" (RGB 255,255,255).

To understand this better, if you set it to black (RGB 0,0,0)
you wouldn't see your image, because remember,
your image lies in the Ambient channel
(and basically you just cut it's lifeline).

Len.

The wait can be horrific, but the outcome can be worse - pumeco 2006