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Is it possible to, rather than a green screen, take a static shot of a background image (e.g. for a Skype call with a fixed-position webcam), and use this static image as the green screen?

So, I would take a photo of my sitting room through the cam, and then be able to use that image as my "green screen".

  • It's not clear (to me) what you're after. Could you elaborate? What is the expected result, using what as inputs? – Jim Mack Aug 20 '15 at 11:44
  • Basically to swap the background of a room out during a Skype conversation. So instead of it looking like we're sitting in the boardroom, you see a static PNG image behind everyone (or maybe even a video feed) – Scott Edwards Aug 20 '15 at 11:46
  • I'm sure Difference Matte technique should be possible in real time nowadays. In order to create a matte afterwards, see this answers: video.stackexchange.com/questions/4306/…. Also sometimes it's called: Imaged based keying, because it's based on Image differencing algorithms, see en.wikipedia.org/wiki/Image_differencing. – p2or Aug 20 '15 at 12:19
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Yes, that is possible. What you're searching for is a difference matte / difference key. For that technique, you supply a base image and the program keys everything out that equals that image. So you could key out your static background so that only you remain in the picture.

However, there are a few downsides:

  • This technique doesn't work nearly as good as a greenscreen. It will probably require a lot of work and there will still be some artifacts left in the video.
  • If you're using a bad camera (such as a laptop webcam), the result will be even worse.
  • If you move your camera even slightly, you'll have a problem. So if you do that with a webcam, don't touch it at all, if possible.
  • There probably aren't many applications that can do this effect live (as opposed to post-production). IIRC, there is some video chat app for Mac-Computers that can do this. I'm not sure if it is possible with Skype, you'll have to research that. However, keep in mind that it probably won't look as good as you imagine it.
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That's an interesting idea, but I expect the result to be of low quality.

I suppose you are thinking about a computer program that compares one static frame of the background with other frames where somebody moves in the foreground. All pixels that are the same in both frames (within some narrow tolerance) will be made transparent for a new background. The static background frame has to be taken from the same video and the camera be fixed to avoid differences due to changes of perspective.

But the problem can best be seen with a difficult scene: Let's take a person with blonde hair in front of a pine wood book shelf. There will certainly be parts of the hair detected as background and vice versa. With a still photo this misdetection may be acceptable, but in a video with moving head and hair the separation between fore- and background will appear as a dancing artifact.

Other scenes may be easier. You just have to increase the contrast between fore- and background for example by using hair lights and exchange a dark original background with a dark new background. And of course film in the highest resolution and quality possible.

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