Matte in surface still renders in alpha

[mdharrington]

I had a situation where I had to render out isolated geometry, but have it blocked by some blocking geometry.

The blocking geometry had a diffuse surface with 'matte' checked

The resulting render had black in the RGB channels for the blocking geometry...but they still rendered in the alpha channel.
Changing alpha shadows had a small effect, but the geometry was still in the alpha

Changing the opacity to zero was the only way to remove it from the render....but it then removes the blocking effect.

Not sure if this is a bug or limitation...I am still on v2.16 as I am in the middle of production

[juanjgon]

As far I know the mate option enable the surface as shadow catcher in the alpha channel, the shadows received by the object are placed in the alpha channel.

Your best chance is to use the render layers, but this a feature of the 2.2 release.
http://render.otoy.com/forum/viewtopic.php?f=51&t=44267

-Juanjo

[mdharrington]

i see...wrong kind of matte

thanks