I believe multi-pass refers to redering in layers... instead of rendering all of the image in one pass it does it in multy-pass...   many passes....  as to exactly what does each pass renders and what does it choose to render ( of the same image) , i don't know...  

I do know that certain calculations are done to render different pixels into imulating certain shades, colors and hues of an image...  not to mention hdr and all the other good stuff renderers do...

Bryce does render in more than one pass as you may already seen....

hope it threw so light...

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