render shadows for compossiting

[timnhe]

Hi!! I’m trying to render a scene that has one character and a ground plane. In Lightwave when i want to get the shadows of the ground, I activate the shadows density in the surface property of my ground object, but is it possible in messiah?

I´m investigating the render groups to make the trick, but I don’t obtain results
Any suggestions? …

Thanks

[isobarxx]

…Edited due to not reading the post thoroughly enough.

[AlexK]

Taken from the yahoo group :

http://groups.yahoo.com/group/pmGmessiah/message/36188

since there’s no shadow pass or shadow alpha channel in messiah yet,
you’ll have to use the old school shadow pass technique, wich consists
in turning all the shadow receiving surfaces black, set the shadow
casting objects to be unseen by the camera, deactivate all lights except
the shadow casting key light(s), deactivate the shadows for that light,
duplicate it, inverse the duplicated light’s intensity (to make it a
negative light) and activate it’s shadows. This way you obtain a black
image with white shadow areas, wich you can then use in a compositing app.
This technique can be a bit tedious, but it works. On the other hand it
has the advantage that you can treat the shadow pass in post, you can
e.g. render area light shadows with less quality, and/or without
antialaising and blur them afterwards in your comp app.

Here’s an example scene to illustrate that technique:
http://maks.free.fr/tech/shadow_pass.mpj

I hope this helps.

[timnhe]

Thanks AlexK, it´s a good Trick

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