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I'm experimenting with "green screen" techniques to remove the background around a test subject. The test shots were taken in front of a bright green background in moderate to bright lighting conditions. I am using the GIMP "select by color" to try to select and remove the green background.

The issue that I am seeing is that there seems to be a greenish fuzz or color spill around everyone in the photo. The range of brightness is quite wide, so I'm finding I have to select many times in an attempt to get rid of this. Worse still, I am having trouble removing this spill at all when it interacts with light colored hair. When I try to select some of the green, it starts selecting significant portions of the picture that I want to keep, mainly hair.

Is there a way to deal with this problem, or am I doing something wrong?

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2 Answers

I would select the edges with a blurred selection and then try to use Color to Alpha with your green screen color. This will remove some detail from the edges though, but it's just what I have occasionally used, someone else may have a better suggestion.

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I don't have a lot of experience with this personally, so take it with a grain of salt, but in portraiture, it is not uncommon to photograph someone against a "pure white" backdrop. One of the problems is that the white blows out the subject if you stop it for the white, and even when the subject is exposed properly, there is a lot of "light bleed" around the neck, shoulders etc. (called "light wrap").

The key to minimizing this is to light them separately, by moving the subject forward, and hiding the lighting for the background behind e.g. folding screens. You set your stops and lighting for the subject as normal and set up the lighting for the backdrop so it is overexposed. You get a very even color field with little spill-over onto the subject.

This will make your chroma-keying in post a lot easier. I will attempt to update with a link regarding the details. [edit: see for instance http://www.zarias.com/white-seamless-tutorial-part-1-gear-space/ ]

Not much help after the fact, but if you can reshoot or use this going forward, your life may be a little easier. If you don't have good separation, you will need to hand mask it.

Additionally, you may be able to take an additional shot with the foreground lights off, creating silhouette image which is easily used as a mask.

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