Shadow Matte workflow

[brurpo]

Hi there! Thanks for your time!

Is there any way for out of frame shadow matte objects to pass through to skydome instead of having a black value? I've tried so many things but couldnt make it work.

The best I could do is use two skydomes, one with full contribution but the specular, and the other with no contribution except specular, then, on the second one, remove the shadow matte geometry from the light link, this way I only get the specular from the skydome.

Still, thats not what I would want, and I still get those odd and simply wrong diffuse contribution from black (or any solid color or texture) from the geometry that is offscreen. maybe I could try something with ray switch.

Disable cast shadows are also out of question, as I would lose the darkening contact shadows on the other objects.

It would be nice to have an option for offscreen geometry to passthrough to the background or be completely transparent.

Am I missing something?

Thanks!

[brurpo · Accepted solution]

So I found a workaround. For anyone with the same problem here is how I came around:

I normally projected the footage into the shadow matte Background, but as shadow matte does not have an opacity channel, I plugged it into the emission of a standard surface with diffuse and specular turned off (black, zero weight). Then, as the projection does not have a default alpha, I used another projection, without any texture, to project a solid white, and use the default color as black, and plugged it into the opacity channel of the standard surface.
Finally, to keep the shadow matte alphas, I used a ray switch to plug the shadow matte into the camera, and the surface shader into everything else.

Here are the differences, standard workflow of just using a shadow matte, note the black where the surfaces goes beyond the camera frustum:

And with this workflow:

It would be nice to have an option on the shadow matte shader to just pass-trough anything that goes off camera. It is a must have to integrate anything onto a live footage.