Video Sequence Editor Alpha problem

I’m having trouble getting the Video Sequence editor to properly overlay an image on top of a movie strip. I’m just trying to put some explanatory text on a little educational video.

I’m putting the text (saved as PNG from GIMP with an alpha) and putting it above the movie clip. When I select “Alpha Over” on the image strip the movie shows through, but the text isn’t properly anti-aliased (the text isn’t as sharp as it appears in GIMP).

So I suspected that I wasn’t saving the PNG correctly, so I thought - I’ll just render something simple using RGBA from Blender itself and give that a try. I used the default scene and just rendered it to PNG with RGBA and then tried it. I could see the underlying movie clip, but it was washed out.

It appears that the “color” in the alpha area is somehow bleeding into the “color” in the underlying strip.

I can’t imagine there isn’t a way around this issue, but I haven’t been able to figure out how to do this. It would seem anytime someone wanted to add some rendered material to a live action clip they would run into this problem, so I’m sure it’s just something I’m doing wrong.

Thanks for any help.

BTW I first noticed this on 2.59, so I upgraded to 2.61 and had the same problem.

I experimented more today and figured out how to solve my problem.

It appears that when you want to use Alpha Over that you should also specify “premultiply” on the strips attributes (Hit ‘N’ to make sure you see the attributes, and then scroll down to the “Filter” section and look under the Multiply field - at least in 2.61)

Hopefully this will help someone else that is fighting with this issue.