Hello.
I’m trying to render an exterior scene where the trees are rendered with diferent setting and then compose it to get the final image.
Well…I made some tests and I know I need to use matte objects but I’m confused about all this.
Does anyone knows a good tutorial on composing?
Thanks 
Wheather you think its any good or not is up to you, but you can try mine.
Thanks Seraph.
Your tutorials are very good but I think they don’t help in this particular case because I’m not trying to composite with a photograph but it’s possible that I missed something.
I just want to render diferent objects of a scene with diferent settings (mormaly to speed up rendering) and be able to merge them again.
Heres a simple scene:
What I want is to render the cylinders separatly wich in a real case could be trees.
One of the things I don’t understand is how to manage overlaping shadows.
If I render the box and plane without the cylinders like this:
and the cylinders with matte plane and box with alpha contribution of -1 and using affecting alpha and shadows:
and alpha channel:
I get overlaping shadows when compositing:
If I render the background (the plane and box) with the cylinders as mattes like this:
I get this a somewhat diferent shadows and “fringe” arroud the cylinders:
I think there must be a right way to do this :?
Thanks again
go with the last one but turn off pre-multiplied in the file format options.