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mbw
01-31-2007, 08:45 PM
Hi all,
I've been playing with a little animation that I wanted to composite with
some DV footage.

* The C4D scene is setup with a character walking across the screen on a floor object.

* The Floor has a compositing tag on it and the checkmark for composite background
has been checked. The color is white.

* I've given the character an object tag of 1

* The I render out a multipass with the RGB, object and shadow passes being rendered
out.

Here is the problem!!!
* In AE I put the RGB on the bottom layer and use the object pass as a track matte. However there is a ring of white pixels around the character that I don't know how
to get rid of them.

Anyone know why this is happening?

Thanks

Mark

Per-Anders
01-31-2007, 08:48 PM
check how you imported the footage (and how you set up your alpha in cinema) if one is premultiplied but the other isn't then that will cause this problem, they both need to be set up the same way, you can try a defringe see if that helps.

sismik
01-31-2007, 08:56 PM
Select your footage and go to Interpret Footage (ctrl-f) in After-Effects. Try to choose Premultiply for the alpha setting

Good Luck

mbw
02-01-2007, 12:22 AM
Per Anders,

I'm trying to understand what you mean here. The object pass is output
as a black and white so I use it as a track matte in AE. Because it doesn't
have any alpha channel I use the LUMA. However, I don't see how to change
the pre-multiply for the LUMA track matte... Does this make any sense?

Thanks for the help.

Mark

Per-Anders
02-01-2007, 12:43 AM
The white ring can come from two things basically.

1) Your object matte somehow isn't hidden in the AE comp (duplictated layer underneath or something).
2) Your original plate had white in it around the character but you're not defringing it.

I was wrong in my previous post, you're not using a compositing tag to create a matte background just to make a white floor. The question is why? It wont affect the shadow pass in the multipass, and as you're comping it out with a mask you don't need to worry about anything that's on it really, all that happens is that you're getting two levels of aliasing going on. First the AA between your figure and the white background in the render, and secondly when you use the matte in AE, but all that means is the white blend is still there only where it was 50% white, it's still 50% white but it's also 50% transparent, what you can try is either the "Remove Color Matting" effect in After Effects effects, or possibly the simple choker effect, or when you render just render with the floor showing the video/image front projected on it so that any fringe/mask will match.

Generally though these days i prefer to use the matte object and "Straight Alpha" when delaing with just a single object rather than object id passes, it's much easier more liekly to get a good result from.

mbw
02-01-2007, 02:43 AM
Per Anders,

Thanks for the note about the matte object. Never knew about that. The
use of the composition tag on the floor was just an experiment which has
failed. What I'd like to do is learn how to have multiple objects in a scene
using the multiple object buffers so that in AE I can put the different
on different layers.

I am trying the matte layer flow right now, but how does one use the
object buffer and such with AE for compositing? It seemed so simple
when I initially thought about it, but I must be wrong.

* create RGB layer and object matte layer
* Use the object matte as a track matte in AE
* Add the shadow pass as a multiply layer

This works except for the white ring.... Hmm.. I'll look at the simple choker,
but that works on alphas I thought and not the luminance of the
object matter layer.

Thanks again for the help.

Mark

mbw
02-01-2007, 02:48 AM
Per Anders,

Unfortunately, making the floor a matte object means that no shadows
are cast on it. I am trying again with the Matte object taken off the floor.

arrrggg

Mark

mbw
02-01-2007, 02:56 AM
Per Anders,
Okay how does one get the shadow pass out... Either I have the
ring of white around the object using the object buffer, but I
get the shadows, or I use the matte object on the floor and not
get the shadows....

Man it this beginning to @!#$%@#%! me off... :-)

Mark

mbw
02-01-2007, 03:35 AM
Okay I figured it out.

You can't use the track matte feature on the composition layer window. You must
use the "set matte" function and then the "remove color matte" to get rid of the
ring. The reason for using the composition tag was made clear to me once I tried
to use the "remove color matte" function. Because the floor was not a uniform white
or black, I had to dial in the correct color. By making the floor a composition background
it renders out as a pure white or black(or whatever color you choose).

Thanks for the help...

Mark

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