Shadows with Alpha

Hello,

Anyone have an idea of how to get a transparent floor with shadows that have alpha in Cycles? Need to make some images where the background can be changed by the client.

Cheers.

Ah, never mind, got it with some fooling around with the nodes. Used a white background and then used the black and white colours to set the alpha for a shadow colour of my choosing. Also used a colourRamp node to tweak the amount of shadow used. I then added a node to test how it looks with different background colours (labelled B.G). Here’s the node setup:


Thanks Alain, looks like the same solution as what I’ve got above, but with some of the nodes switched around a tad.