How to eliminate dark edge from green screen?

philanyware wrote on 8/22/2010, 1:39 PM

Hi,

I'm trying to use a green screen to create a cut out video with a white background. After applying the chroma key effect I get a dark edge around the subject.
Can anybody advise how to eliminate it?

Here's the image before applying the chroma key:

and after:

I guess the edge around the white shirt is not such a problem because I can wear a dark shirt, but I don't know what to do about the edge around the face.

I've applied a chroma blur with hor & vert set to 1 plus a chroma keyer with rgb=0/166/173, low=0.242, high=0.715 and blur=0.

The green screen is lit with a 200W work light on each side at about 30 degrees and the subject is lit with a 35W halogen on each side (fairly close). I've tried a few variations of back light from a small fluorescent tube to a 50W halogen immediately behind the subject and it seems to have no effect on the dark edge.

Shot with a Logitech web cam, Quickcam Pro 9000.

Can anyone help?

Note that I'm new to shooting video and Sony Vegas so if you use a technical term please explain it.

Many thanks,
Phil

Comments

Eugenia wrote on 8/22/2010, 2:04 PM

Download the free Aav6cc plugin and saturate the greens only. Then, retry.

Tim L wrote on 8/22/2010, 2:49 PM

Are you using the webcam in the highest possible resolution? (1600x1200) Higher resolution = smaller pixels = better edges when keying.

In the photos you posted, the dark edge seems to be present in the original photo as well.

While your lighting looks pretty good, I think most pro setups would include a "hair light" or "rim light" for keying (not that I'm a pro -- I just read stuff on the internet). A light mounted above the talent and somewhat behind them -- maybe on each side -- will make a bright outline at the edges which is usually less objectionable than a dark outline.

philanyware wrote on 8/22/2010, 5:14 PM

Thanks Eugenia, that helped a lot. I still have the edge around the white shirt (but I can wear a dark shirt) and the edge around the face has halved.

philanyware wrote on 8/22/2010, 5:21 PM

Thanks Tim.
No, I was recording at 960x720. Will increase it to the 1600x1200. This makes sense and I'm sure it will make the edge even thinner so it should be fine now with Eugenia's tip.

I did try about 35 different combinations with the back lighting and nothing I tried seemed to help the dark edge. I even put a magenta filter on the back light to counter the green reflection from the green screen. It just put a glow of magenta inside the dark edge.
I guess this is called experience.

ADB wrote on 8/22/2010, 5:59 PM

Phil,

To me it looks like "spill". You can remove it using Blender and the green screen plug-in with spill reduction. There's an example here:
http://sites.google.com/site/paprmh/greenscreen

philanyware wrote on 8/24/2010, 11:00 PM

Thanks ADB and nice guide. I'll work my way through that once I've re recorded the video.

Is it generally considered easier to prevent spill like this or clean it up afterwards?