Multiply adding brightness

[YoyoBoy]

Not sure if this is an AE question or a VRay question, but does anyone have any idea why, sometimes in AE, when I set a layer for Multiply, it will actually add brightness in some areas? My AO pass is doing weird things. It might have something to do with my telling the Dirt map to ignore transparency (because it's only brightening the the area behind some glass), but if it were Photoshop I don't think it would be doing that. Or maybe it's just a 32-bit thing?

Thanks

[instinct]

Well this usually means that you have values above one. That would raise values of course.

Cheers,
Thorsten

[YoyoBoy]

I just solved the problem by tossing a "Black & White" effect onto the layer. I guess I don't understand what "Multiply" means. I thought it could only reduce brightness.

[instinct]

Multiply just multiplies the colors. So if you have one color of white (1.0) and one of mid gray (0.5) you get 1.0*0.5=0.5. It does that for all channels on their own.

Cheers,
Thorsten