save shadow isolated (png for instance)

[kostenurka]

Hi guys!

Do you know efficient way to save projected shadow on the ground only? I would love to have pure shadow on the ground saved as PNG as alpha!

thanks!

[Micha_cg]

In the past I rendered the ground from the bottom view and a single sided material (so lighting and shadows was shown at the bottom). Than I use this rendering as alpha texture for the ground. I don't know it's an efficient way, but for an animation it can be very useful.

[kostenurka]

Hi Micha,

I remember you shared this idea long time ago and I tried it out..

At the moment I retrace the shadow in ps using path, bring it to another layer, gaussian blur, transparency.It takes me up to 5-6 minutes and I prefer it (not for complex geometries of course) than what you propose as it involves test renders, material creation, mapping which is longer at the end.
Efficient way would be less then 5 min

[fpedrogo]

You can also save a the shadow channel. Then use that channel to place the shadow in photoshop or any other post processing software.