#Foreground Help!
6 messages in this thread
John,
I'm having trouble with the foreground alpha compositing in Lightwave. In
short, I can't get it to work! Any experience with it? I posted
another message to all that gives more details.
Thanks in advance, Mark C.
Foreground Alpha works a little bit differently than it seems.
Here's how you think it should work: The Foreground Alpha (F.A) image
determines the amount of the Foreground (F) image that is cut out
revealing the objects and/or background. Therefore White in the F.A. image
would cut through 100% of the F.Image and reveal what's behind. Black in
the F.A. image would not cut through and you would see the F. image
completely.
Here's how it does work: Pretty much the opposite of the above. Think of
the F.A. image as determining the amount of the F. image that is
composited over the background stuff. Therefore white in the F.A. image
means that in those areas 100% of the F. image will be revealed over the
background. Black in the F.A. image states that 0% of the F. image will be
composited or seen over the background – therefore you would see all
background here.
Here's how you usually want to set up the images:
Background image: Your background sequence
Foreground image: Your objects rendered OVER black (Saved RGB data) F.A.
image: The alpha channel of the saved RGB data.
Hope this helps…If not, I can clarify…
P.S. Mind if I use this one?
JG <<<<Shake, Rattle & Roll!>>>>>>
John,
Thanks for the reply. Your explanation is correct, the problem I
have however is that the Foreground objects should not have to be
rendered over black, If there is black there in the Foreground Alpha
image it shouldn't matter what was there in the F image. Say for
instance I render an animation on a color backround that I decide I
don't like, If I saved the Alpha images is should be a trivial matter
to recomposite over another background, but it doesn't seem to work
if there is anything BUT black as the original background of the F
image. This is how it seems at least, and thats inconsistant with
the concept of alpha compositing in any other package I've used.
My current application is this: I've digitized many seconds of video of a
girl standing in front of a white background. She is supposed to be mapped on
torn paper as the top layer of a heavily composited scene. So I paint a torn
edge matte just slightly larger than her outline slap her in the forground
layer using the matte to "disappear" all the other white around her RIGHT? NO,
unless I first composite her over black in Adpro it doesn't work. And thats an
extra step I'd rather not take.
What am I doing wrong?
Thanks in advance. Mark C.
Next time I talk to Allen I will ask him about this and see what he has to
say…
JG
John,
Latest update: direct from Jason at Newtek, foreground alpha doesn't work
right. You have to composite before you composite 8(.
Doesn't make for much of a Dear John eh? Use it if you like.
Thanks Mark C.
OK.
I'm still going to talk to Allen and see what he has in mind to take care
of it…
JG