View Full Version : Unseen by Cam, but seen in Alpha Channel ?

12-03-2004, 02:34 PM
How can i do this ? I have a room to which i now need to add an animation of a rotating fan, so i used the same scene of the room but made all objects unseen by camera, except the fan; worked fine so far. But the fan is partly hidden behind a column, which is unseen by camera too and so also unseen in the Alpha Channel.

My half solution so far is to make the column a black matte object, but of course the black column is now visible in the reflections. That way i have to render the animation twice, first the visible one and than the Alpha Channel.

How can i avoid this and render the animation including the correct Alpha Channel in one go ??

12-03-2004, 09:36 PM
Use 2 column objects, one Matte black and check unseen by rays, and with the other textured column check unseen by camera. Neither need to show up in the alpha as long as they occlude parts of the fan from the alpha.

12-04-2004, 02:25 AM
Thanks, thats another interesting solution. Maybe a feature request for "unseen-by-camera-but-seen-in-alpha-channel" would be a good idea.

12-06-2004, 01:55 PM
did you tryed all options in alpha channel ? You can do great tricks by combining those alpha channel options and unsen by camera/rays.

in object propertyes you have "Use surface settings" , "Unnafected by object" and "constant Black"

Unnafected by object for colum should work nice :).

12-06-2004, 02:39 PM
Maybe a feature request for "unseen-by-camera-but-seen-in-alpha-channel" would be a good idea.

Well they say "it's not a bug, it's a feature" - maybe we can use the ray-trace transparency bug - turn it on and it gives you a solid alpha at any level of transparency...