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CiF
12-29-2002, 11:35 AM
Hi, HELP NEEDED (3ds max5)

I need to composite a 3D object rendered with the light tracer
on a 2d background.

Seems Easy ... but !

here is the scene:

A cube.
A ground and a wall are matte/shadow.
with just a skylight.


If I render this object on white, its perfect.
But I need black bg for compositing reasons.

If I render it on black, the shadow are grey
and in the rgb channel !!!

So, when I composite on top of the 2D bg,
I get those grey shadows over the bg!!

Of course I can handle this in a compositing software,
with some tricks using the alpha of the object only...
But, I apply some filters in compositing so with this trick,
I got lots of bugs due to alpha outlines... if u see what I mean.

Actually it seems that the matte/shadow material doesn't
work with the light tracer....

I check the adv. Lighting properties (cast shadows and receive illum) but it doesn't really help the problem.

A way boring way to solve this would be to be able to cast the shadows without rendering the object, but I'm just enable to do that. Before I used a blur material made for that, but it just work with raytraced shadows. The matte/shadows can't really do that cause it just "erase" everything inside the object alpha.

Maybe its a bad idea to use the light tracer for a indoor scene?
Maybe I should use radiosity ? (I never really try this) (seems very technical)


Whaouh! I just read my msg ... its not very clear !!!
I hope someone will understand all this !!!
Even BETTER !! I hope someone already got this pb and have a good solution ...

let's hope ...


To sum up all this, I have 2 questions :

1- is there a way to get the light tracer rendering with all the shadows in the alpha channel only ???

2- Is there a better way to make this VERY SIMPLE composition?
with a rendering quality at least as good as the light tracer.


lookin for any hints, help, tricks ... PLiiizzz

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