I created an animation that looks great except the shadows hardly show on the prop ground I am using.  I want to make an extra pass at the animation but just render the SHADOWS ONLY on the groung using Current BG Shader in the render settings so I can overlay this onto the anmimation.

In order to do this I need to create stronger lighting. I do not want to render figures or anything else - I need these invisible but to get the shadows I need the figure ON.  Is there a setting or way to have the figures cast shadows only?

In the firefly render window, check the box next to "cast shadows only", and that should work.

Yes that works EXCEPT it creates the shadows on a white background. Since I will be compositing I prefer to have this on a transparent background like you get when you render to images (PNG).  I can do it this way but then I will be forced into chromakeying out the white background. Is there a way to have the shadows ONLY without the background?  My settings are Render Over:current BG shader with the Shadows Only box checked. tks.

Save it as a .png file and then in your graphic program apply the shadow  image to itself as a mask in order to get rid of the background.

I have 72 frames of this so that is not workable.....I have found a way using shadow catch in the materials room - it gives me what I want but I have dozens of mats that would need this turn on for.  Don't suppose you would know of a script that would do this? There is a wacro setup but it only affects the current mat.....just like checking the box --- surely there is a way to apply to all mats....