Slightly dark outline of feathered Bezier masks

Tech Diver wrote on 10/2/2007, 8:46 AM
I have encountered an issue with the feathering of Bezier-masked images as follows:

I have some still photos taken during some recent scuba dives that I am "animating" by using two copies on different planes moving at different speeds. Specifically, let's say I have a scene of coral with a fish in the foreground nicely suspended in the water column. Using a graphics editor (Paint Shop Pro) I eliminated the fish from the one version of the photo (this will be the background), and placed and unaltered version of the photo in the foreground in Vegas where I use a Bezier mask to isolate the fish. I then pan the two images so the foreground fish is moving slightly faster than the background coral to add a little three-dimensionality to the composition. This works great.

The problem I have is that the outer-most edge of the Bezier-masked fish has a distinct darker outline, especially when feathering is used. The feathering issue becomes particularly important when the foreground subject is a scuba diver who's bubble column does not blend in with the surrounding water. Note that the darker outline is not present throughout the entire feather zone, but only where the outer-most part meets the background. What causes the slightly darker edge and how do I eliminate it?

Edit: This was using V7e

Comments

Former user wrote on 10/2/2007, 8:53 AM
What color is around the fish that you use the bezier mask on?

Seems like it would be easier to isolate the fish using the paint program and use an alpha channel to place over the background.

Dave T2
Tech Diver wrote on 10/2/2007, 9:03 AM
The fish is surrounded by a consistent color of blue water. Here is an experiment that proves there is a problem. If I take two identical images in identical positions, create a Bezier mask in the foreground, the outline will be slightly visible. Feather the edges and it will be more visible. This should NEVER happen.

Yes you are correct that I could eliminate the area surrounding the fish, diver, etc, in the paint program and have some gradual alpha blending (important for the diver's bubble stream).
Grazie wrote on 10/2/2007, 9:14 AM
Can you post a still? Please? G
Tech Diver wrote on 10/2/2007, 9:18 AM
Yes, I'll post an image later tonight.
Grazie wrote on 10/2/2007, 9:21 AM
Kool! I'd like to see it. Even in London, where it is 05:38pm!! - G
Tech Diver wrote on 10/2/2007, 10:03 AM
Well, you'll probably have to stay up a bit late (or get up real early) since my time zone is GMT - 5hrs.
Former user wrote on 10/2/2007, 10:26 AM
I have Version 6, so it probably is not relevent, but my mask works fine.

Just to be sure though, you don't have SHADOW or GLOW enabled for that track under TRACK MOTION, right?

Dave T2
Tech Diver wrote on 10/2/2007, 11:56 AM
No shadow, glow, or any FX.
GlennChan wrote on 10/2/2007, 12:52 PM
With certain FX, you need to have them applied before masking.

To check for that:
Go into event FX
click the little triangles in the bottom left corner of that window. This changes the "pre/post toggle".
24Peter wrote on 10/3/2007, 2:38 PM
I've run into similar issues with Bezier mask in Vegas 7. Just try brightening the foreground object a bit to see if the boundary disappears. But agreed, this is an issue.
Tech Diver wrote on 10/4/2007, 9:34 AM
Sorry I haven't posted a still to show the phenomenon. The problem seems to be visible right where the outer edge of the feathered Bezier mask meets the background. If I had to guess why, I would venture to say that the alpha blending that takes place over the feathered region is linear. As such, there is a discontinuity in the derivative of the image color/intensity. What we need is a smooth transition accomplished with an "ease-in/ease-out" curve just like the kind that we can select in our video and audio fades.

Perhaps someone at Sony can verify my hypothesis.
GlennChan wrote on 10/4/2007, 12:49 PM
How the feathering falls off looks like it has the "smooth" curve applied to it (like the smooth setting for keyframes). If it was linear it would look bad.

Did you try pre/post toggle? This will cause dark outlines with certain FX (e.g. color curves).

2- Can you post a still and/or a .veg?