Matte Element

[glorybound]

How do I isolate my matte shadow? I want control in post. Now, it comes in black.

[Svetlozar Draganov]

There is a Matte-Shadow render element which could be used as a mask to control the opacity of the matte-shadow on post:

[glorybound]

There is a Matte-Shadow render element which could be used as a mask to control the opacity of the matte-shadow on post: <img src="http://forums.chaosgroup.com/attachment.php?attachmentid=21851"/>

I found that, but it seems to control all the shadows in the scene.

[Svetlozar Draganov]

Yes that's true - I always forget that the Matte-Shadow element contain information about the non-matte shadows as well.
Fortunately Shadow element doesn't contain information for the matte-shadows so if you extract it from MatteShadow one you'll get the right mask.
I can show you how to do it Nuke but I am not sure if there are alternative tools in Photoshop.

The Shadow element cannot be subtracted from the MatteShadow one out of the box since it has different values for R/G/B while the MatteShadow doesn't.
You have to adjust Shadow element first to be like an Alpha channel not like a RGB-one. In Nuke this could be done via the Clamp-node.

Here how the passes looks like out of the box.

With the help of the Clamp too I could convert the Shadow pass to Alpha:

Then if you subtract this pass from MatteShadow one you will get only the matte-shadows-mask:

And then you can use that mask to control the transparency of the matte-shadow without affecting other shadows:

[glorybound]

I'll have to see what I can do in PS, thanks.