View Full Version : render a shadow on a alpha plane?

08-20-2010, 12:16 PM

I have to do a few renders of buildings for a client. The problem is, the client wants that the buildings cast shadows on the ground, but the whole ground should be transparent so he can later change the color.

I tried to render the buildings on a 30% transparent plane, but then the plane is still white and its not comfortable in Photoshop to change the color for the whole ground (and the shadows on the ground)

I would be glad for every tip, thanks in advance.

08-20-2010, 12:27 PM
Surface Editor-Advanced tab.
Change the Alpha option for the ground surface to "Shadow Density".

Now render with the building "unseen by camera" (but be sure the rays still see it, or youŽll have no shadows at all!)

Done. You got your shadows pass for the ground.

Elmar Moelzer
08-20-2010, 12:29 PM
I hope I understand you correctly.
You want to have the surface of the ground transparent, but still catch shadows so that your client can replace the ground himself in PS?
If so, make the Ground surface all black. Then go into the advanced settings in Surface Editor and set the Alpha Channel to Shadow Density.
Hope that helps.

Edit: Dang, Netvudu beat me to it.

08-20-2010, 12:52 PM
works perfectly, thank you both very much for the fast help :)