Color as alpha not black

I d like to understand how to mix (i suppose in a group node) different quads where there are black shapes on a colored background.
I know how to mix colored shapes with a blakc background with a blend node as render state. But now how can i mix black shapes so that the result is always black when at least one pixels in the same position is black? Pixel at the same position should be colored only when the all the pixels on the same position the inputs are colored.
(dunno if it makes any sense…)

multiply blend mode?

well it’s easy to convert to pixel shader if you do a clear statement
but for some more detailed explanations i think you need to put on photoshoped result and a sample of source pictures… or just a patch with it all…

Ok, got it, Blend Node (Multiply) on all except the first (left most) Quad/Layer.
I was using the Blend Node on all the layers, that s why it didn t work.

EDIT: and a patch added

BlendMultiply.v4p (24.7 kB)