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CiF
12-29-2002, 09:22 AM
Hi, :buttrock: HELP NEEDED :buttrock:

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
CiF
12-29-2002, 09:27 AM
this sucks :annoyed:
Dr BeN
12-29-2002, 12:54 PM
well i dont know anything about lighttracer .. ;) soory but i know a little bit about maya and in maya it's know porb as far as i know ... any change to port the scene to maya ?!
CiF
12-29-2002, 06:23 PM
Come one !!!

Everything is ready in MAx, I'm not gonna switch to maya for that ...

Does anybody know if a plugin can solve the problem ? brazil, final render ... ???
lostfilez
12-29-2002, 07:22 PM
Well, you could just take the 2d image you want to composite onto and set it as your environment. Just do it all in one step rather than 2 or 3. I don't think it has anything to do w/ the light tracer. You're just doin it the hard way :D
CiF
12-29-2002, 08:23 PM
eheh :)

lostfilez you should try it !!! AND you will see the result :

GREY SHADOW OVER THE BG .... THAT's the problem ...


thanks anyway ....
ramis
12-29-2002, 08:31 PM
Hey your problem is hard to understand :surprised
I think it's the same problem I had, look at the thread I started some time ago, it has only one reply but it solved the problem :)

http://www.cgtalk.com/showthread.php?s=&threadid=29804

Hope it helps.
CiF
12-29-2002, 08:41 PM
thanks for helping ...


But as I write it in my post, I already try this trick ...

and it doesn't solve the problem, I mean you still have those grey shadows in the rgb channel ...

to solve the pb, the rgb channel should only content the object colors, but no shadows. the shadows should only be visible in the alpha channel ...

Am I right ?

thanks again for relying Ramis ....
orangefisk
01-08-2003, 10:49 AM
Me gettin' blind...

"Hmm - dunno if this works... What would happen if you made two renders and then composed them afterwards. In the first render you add a matte/shadow material for the objects - and in the second render you simply remove shadows from the floor..."

Sorry - didn't see "matte / shadow doesn't work..." - Doh
CiF
01-08-2003, 10:54 AM
Actually here is the real problem I have :

http://www.cacaocif.com/anims/worst-chall_greyl.jpg
CiF
01-08-2003, 11:02 AM
one solution would be :

to be able to set the matte/shadow object in a way that he can not receive shadow from one object (the plane), but still receive shadows from the other object ....

But I not able to do that in MAX :buttrock:


Another solution :

to get rid of the plane and to put a map as a projector in the light
It work fine .... but its impossible with area light :buttrock: :buttrock:

I just have a lot of solutions that doesn't work for one reason or another ...
I get the result I want with some compositing tricks, but that what I'm trying to avoid ...



Damn .... such a f..bip..kin problem !!!
visualasylum
02-21-2003, 03:55 AM
CIF,

first off, you're not so clear about this thing.

If you're rendering with shadows, I assume you need the shadows to be casted on the 2d Background. SO what's the problem if those shadows show up?

I think you're not explaining well. please take 20 minute to describe yourself and the situation, use samples of the alpha, and
let me know what you need, and I will try to help.

I read your message 2 times, and didn't make sense.

cheers,

visualasylum
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