Junk mattes
by lilireed
on
Sep 25, 2007 at 8:39:19 pm
Hello
After seeing Aharon Rabinowitz's podcast on super tight junk mattes I have been using them with some success. Unexplicably in my last project, when I autotrace my subject the masks trace the upper half of the body perfectly, and arbitrarily "cut" my person with a straight line at around the waist, in such a way that I only have the top half masked.
It is quite strange because when I preview the mask in the autotrace settings the mask covers everything, and even leaves the whole body traced on the first frame once I hit OK, but then cuts the body in half for all subsequent frames!!!!
I really don't know what's going on, it hadn't happened before.
Re: Junk mattes by Dave LaRonde on Sep 25, 2007 at 9:52:42 pm
[lilireed]"...when I autotrace my subject the masks trace the upper half of the body perfectly, and arbitrarily "cut" my person with a straight line at around the waist..."
That's weird. Well, what kind of background is the subject against? There isn't some goofy thing happening in the background about waist-high to the subject, is there? Or is the color of something too close to the key color -- is the subject wearing blue pants against a blue background?
Have you tried fiddling with your initial key, then trying auto trace again?
Re: Junk mattes by lilireed on Sep 26, 2007 at 1:53:10 am
Actually, the line cuts through the person quite arbitrarily, half way across her jeans, and the key really does only keep the background out in all the frames, only the mask that "cuts off" in a straight line at a certain hight. Could ir have anything to do with the fact that I've rotated the footage 90 degrees? It's the only thing I did other than changing the contrast and keying.
Re: Junk mattes by Dave LaRonde on Sep 26, 2007 at 2:41:48 pm
Well, I can't explain it. I rotate shots 90 degrees all the time and key them.
But what's it going to hurt to key the shot and do that autotrace voodoo BEFORE you rotate? Heck, maybe there's some goofy thing going on if you autotrace after a rotation.
-- OR --
Myabe you could use my take on Aharon's Supertight Junk Matte procedure:
Re: Junk mattes by Dave LaRonde on Sep 26, 2007 at 3:37:14 pm
Oh, I should hasten to add that the resulting comp should be nested into a second comp, and you then pull a key from the very narrow chroma key background surrounding the subject.
Re: Junk mattes by Dane Hession on Nov 24, 2008 at 7:26:41 pm
[lilireed] "...when I autotrace my subject the masks trace the upper half of the body perfectly, and arbitrarily "cut" my person with a straight line at around the waist..."
This same thing happens to me now that ive switched to cs4 and HiDef.
If any one knows why it would be a big help.
