Feeding green screen chroma key into Skype

I wanted the remote Skype viewer to see whatever image I wanted behind me: a brick wall, a rack of computers, a bookshelf, a logo, a moving pattern...whatever.
Written by David Gewirtz, Senior Contributing Editor

All projects: DIY-IT Project Guide This project: Build your own, broadcast-quality Skype Studio

I had some very specific software requirements for my studio, and I have to tell you, finding software to meet my needs was no easy matter. Most specifically, I wanted to be able to feed a post-chroma key image into Skype.

Now, what the heck does that mean?

Skype is a voice and video chat program. It takes input from a camera and sound device on your computer and sends that combined video/sound signal to another, remote Skype client.

So far, so good. The problem was, if I pointed a camera at my head with a green screen behind me, Skype would take the video from the camera and send it, unmodified, to the remote Skype user. The remote Skype user would see my handsome face, with a field of green behind me.

This is not what I wanted.

I wanted the remote Skype viewer to see whatever image I wanted behind me: a brick wall, a rack of computers, a bookshelf, a logo, a moving pattern...whatever.

See also: Getting started with green screen

So I needed software to accomplish two things: merge a background image and my camera image into a seamless whole, and somehow insert that into Skype's video stream as if it came that way from a camera.

Introducing CamTwist

I tried a lot of software products, on both PC and Mac. I found one program on the PC, ManyCam, which did some of what I wanted, but it was limited, in that it would only do certain effects, and it didn't have a way to work with studio software -- software that would do things like provide lower-thirds titles, multiple talking heads, and so forth.

And then I found CamTwist Studio. CamTwist claims to provide 50+ built-in effects and turn your Mac into a studio, but I found that both the effects and the studio elements might be fine for a podcast, but they didn't meet my broadcast-quality standards.

But CamTwist does two things that make it essential. First, it provides its own camera driver, fooling Skype into thinking that CamTwist is a camera. When I select the camera in Skype, I'm really selecting CamTwist.

Then, CamTwist does one other, completely unintuitively important thing: It can take anything on the Mac's desktop (CamTwist calls this Desktop+) and use that as the video source.

That means that anything you can watch on your Mac can become what you feed into CamTwist, and then, by extension to Skype.

Think through the possibilities. With CamTwist, all I had to do was get something to look good on my Mac's desktop, and that could be my Skype video input.

There are some disadvantages to CamTwist. It hasn't been updated in a long time. It works in Lion, but just. Back on March 3, 2012, the author wrote that he's intending to do further development, but he hasn't posted anything since.

This spotlights one of the most serious risks of the Skype Studio. It depends on individual products that work on specific releases of the OS, for which there are no known substitute solutions. If one of the many items in the chain fails, the studio may fail with it.

It's a risk I'm taking, but it does sometimes keep me up at night.

Introducing BoinxTV

CamTwist is free. BoinxTV is not. BoinxTV is $499. But if CamTwist is a necessary slice of the pie to provide camera input to Skype, BoinxTV is the rest of the pizza.

BoinxTV is nothing less than a software broadcast studio, and it's quite amazing.

In a later article, I'll describe all that BoinxTV lets me do, but for now, I'll simply say that it allows me to do live, dynamic post-production -- while the show is being recorded.

That means when I'm done recording a show, I don't have hours or days of post-production where I have to sit in front of Premiere or Final Cut, layering on each element -- it's all done for me while the show runs.

More on that in a future article. For now, let's focus on chroma key.

CamTwist has a green screen chroma key function, but it's quite primitive. It lets you select a single green HSB value and mask it out.

But the real world isn't like that. Even with a vivid green screen behind you, the camera picks up all sorts of color variations, based on where the light shines, how much light shines, even the softest shadows, and the like.

See also: Green screen lighting in the Skype Studio

When I tried using CamTwist for green screen, I kept getting blotches.

But when the Boinx people kindly sent me a test copy of BoinxTV, I discovered it has a very sophisticated set of chroma key settings, which allow a great deal of customization and subtlety. It also provides additional post processing to remove the reflective green fringe that often gets picked up by the camera when light bounces off the green background and lands on the back of the subject.

Connecting BoinxTV to CamTwist to Skype

The way I get the BoinxTV output into Skype is amazingly simple. I just keep a preview window open on the desktop as BoinxTV runs. I then tell the Desktop+ feature of CamTwist to grab the contents of the BoinxTV window. And I then tell Skype to use CamTwist as the camera.

It actually works, and works well. The neat thing is that since CamTwist becomes a software camera, I can use it as input to other programs as well. When I had to give a lecture to National Defense University, and they only use Google Chat, I was able to tell Google Chat to use CamTwist as the camera and it all worked.

See also: Technology policy challenges faced by the U.S. Federal Government (video seminar)

Of course, this is just the video component. There's also sound. But that's a story we'll save for another day.

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