To summerise what I have written below:
I have used a bit of text create two masks, when I place these on top of each other there is a visble outline, as if one is slightly bigger than the other (although masks were creating using the same image).
This is the full story:
I have a project where I am trying to recreate some graphics with 3D elements for a reversioning. The main problem is that the we only have a 2D image taken from the textless elements, and I have to make the graphics pass through some text (from behind to infront).
To do this I have created some text as an image with alpha and used that to create two masks.
One mask is simply just to get the right texture for text when the graphic is behind.
The 2nd text mask is placed over the graphic and exported so I have a mov of just the bit of graphic that can be viewed through the text.
For the final part I have place the graphic in the background, place the text with the texture on top of that, and the mov of the mask is placed on top of the text with 0% opacity, key framed up to 100% as the graphic 'passes through' the text. So the text with texture should be completely covered by the mask of the graphic, making it appear as if the graphic had moved in front of the text.
However, there is thin edge visible on the text. The same image (text with alpha, created in motion) was used to make both masks, so one should cover the other exactly (right?)
What could be causing and how can I get rid of this outline edge?
I've managed to get the edge out of the final video now. I also found a slightly better way of explain the problem.
It seems the image mask has a bit of the alpha channel 'bleeding' through on the outer pixel of the mask. When this mask was put on top of the text, which was bright it caused the outer pixel to let some of the brightness through.
Here's my workaround:
I redid the 2nd mask using a copy of the text with a glow so it was bigger, when the opacity was faded up the parts outside the final text are camouflaged in the graphic behind the text.
Not too difficult in the end, but I'm sure it's not the idea way to do such a task, so still advice and explainations would be great to hear. Why there is there a bit of alpha channel on the outer pixel of an image mask (if that is the case)? Where else could the edge of the the mask?
Sorry Terry, I re-read your post a couple of times, but I'm having a very difficult time visualizing your situation. If you could post your project, perhaps I could tell you if there's a different way to do it, but I'm really not sure what look you're going for.
As far as the edge pixel of text being partially transparent in your image mask, that sounds like aliasing to me, but again, I think I'd need to see the project (the non-working one, not your workaround) to be sure.