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Replace any Green Screen Background Using a Chroma Key

Without a doubt, you see chromakeys used countless times - probably every time you watch the news on TV - and perhaps you aren't even aware of it. Chromakeying is a process widely used throughout the television industry to merge (composite) one image (often a live one) with previously-shot footage or graphics and make it look perfectly natural.

Read the full article The ABCs of Chromakeys.

Video Transcript

Hi, I'm Tom Benford, your Videomaker du jour, and today I'm doing a tutorial for you on the ABCs of Chromakey. As you can see, I've spared no expense. The background we're using is my garage door, but actually the background doesn't make any difference because once we have our green screen background put up, the background can be anything you want, which is the whole point of doing chromakey.

This is going to be an abbreviated tutorial because the weather here in New Jersey is about 52 degrees today, so it's a bit chilly. The chromakey software I'm using is Adobe Ultra 3 and the screen captures were done using Hyperionics Software's Hyper Cam 2, and that's available at hyperionics.com. The backdrop that I'm using is a 4 by 6 foot piece of green polyester fabric that I got at a local fabric store for under $30.00. I like using the polyester because it's wrinkle-free, so you don't have to iron it or store it any special way, the wrinkles fall right out. It's lightweight, easy to store, and easy to put up too. In this case, I'm just going to be using some pushpins but you could also using masking or Gafford's tape too. Why don't I get the backdrop up and then we'll pick it up from there.

Okay, so here we are back again, now with the backdrop in place. Once again, you're seeing a green background here, but in the final video this will be replaced with scenes of sunsets or other stills as well as virtual sets and maybe some moving footage also, to illustrate what you can do with chromakey. In one of the segments, I'll have something in the background here so I'm going to point back to it, and then when we drop it in, the whole thing will make a little more sense. So this is facing my left right now. By the same token, there are things that I may want to put in the background that will be over my right shoulder here, so I think you're starting to get the idea that there are a lot of things you could do with chromakey.

And now we should have enough video footage for us to go in and start working inside where it's warm and doing our computer magic. So without further ado, see you later, bye.

All righty, here we are in Adobe Ultra, and the first thing we're going to do is load an input image. I have all the elements we'll be using in the subdirectory called Clips 2, so that's what I'm navigating to right now, and the particular file type is wmv, so I'm entering in *.wmv to bring up a list of all those available file types. There we are. The one we want is called backdrop. If you remember, I shot the backdrop segment in front of the garage door after I put the green backdrop up, hence the name.

Going to the keyer section, I select enable. Now I'm going to select some points in the background that we want to key away. The reason you do this is to compensate for any light or dark areas and it enables Adobe to average them out and knock out the various shades of the background that have these variances in them. So I just went around the perimeter on both sides of my heads – my head rather, and clicking on apply points goes and knocks out the background just like that.

Next thing to do is load a background image. I'll be using a stock African sunset image from the Adobe collection that comes with the software, and voila, there we are. If you notice on the preview, however, you can see some of the background image shining through and that's compensated for by going back to the keyer menu and adjusting the transparency. You will also see a slight halo around my head and around my body, and that's easily compensated by adjusting the mask itself. There are a number of adjustments that you can make to adjust the image. There's a quick preview, it doesn't look too bad. We could tighten it up a bit more, but once again, this is the crash course.

Now, let's say you don't want a still image, you'd rather have some moving footage in back of you, well, you simply go back to the background menu and select an appropriate clip. Once again, all our goodies are in the Clips 2 subdirectory, and I have a number of moving clips that we can use. And again, their file type is .wmv, so that's what we're looking for. The particular one I want to use is a parody on River Dance with a chorus line of chimpanzees doing the footwork, and there are the boys right now. It's called Dancing 3.

Once again, if we go to the preview pane, we can get a look at how the images look when combined there and make any adjustments by shrinking or sharpening or softening the mask. At this point, you can also add shadows, adjust the highlights, you can compensate for the color, the saturation hue, any number of parameters can be adjusted to make the combination of the two images look more complementary and certainly look a bit more convincing.

I don't think this looks all that bad considering that, you know, this is just a quickie here, so I am clicking on the preview screen, that looks pretty good. A bit outlandish but this just illustrates some of the amazing things that you can do using chromakey, and you can have a lot of fun using the software as well. It's certainly an element to increase your creativity and one that you definitely get better the more you use it.

Okay, now we're working on the second segment, which is facing left and that's the name of the input clip that we'll be getting. And once again, it's a wmv file, and when it comes up we go into the keyer section again and select our key points, which we are doing once again to compensate for any irregularities or differences in the hue of the green background. And once that's done – as you can see, I'm just randomly going around trying to cover all bases here, once that's done we go and click on apply points, once again, which makes the chromakey mat take effect.

And now we're going to load one of these virtual sets, in this case, it's going to be the library and the particular segment that I want to use is called Library Cam 2 Tight. So there we are. Now, as you can see, you can see the library set background through my body and once again, we're going into the transparency application of keyer and adjusting that so that I'm solid. There's also a little halo around my head which we'll take care of now with the shrink slider.

I want to use a video segment to put on the inset and that's called 17sec.wmv. This is some footage that was shot back in 1995 on high eight when I was Rachel, Nevada hunting down UFO people and Area 51. The test looks pretty good so I think we're good with that and we're gonna go with it.

Okay, back once again in Ultra 3, we're going to do the segment that I shot pointing over my right shoulder. So we're loading that clip, it's a wmv file called Right, and once we get it up we will go back once again and select our points using the keyer, and again, this is to take care and compensate for any variances in the shade of green that we're going to be keying out. That's in, we applied the points.

Now, we're going to be selecting one of the virtual libraries, the museum, and the particular segment is Museum Cam 8 Tight. Rather than using the Monet painting on the wall, I'd like to substitute that with a picture of my German Shepherd dog, Major. And I have that jpeg in the Clips 2 subdirectory, which I'm navigating to. I will specify an *.jpeg file type and there it is. So we click on it and now that appears in the painting. To give it some additional realism, we're going to add some shadows. So I go to the shadow menu and I select wall and floor left and you can vary the opacity. See I made it darker. You can also move the shadow around any way you want to get the effect that you're looking for. Try a little test, that looks pretty convincing, so I'm happy with it and I think we're gonna go with that.

Okay, so here we are back again, now with the backdrop in place. Once again, you're seeing a green background here, but in the final video this will be replaced with scenes of sunsets or other stills as well as virtual sets and maybe some moving footage also to illustrate what you can do with chromakey. In one of the segments, I'll have something in the background here, so I'm going to point back to it and then when we drop it in, the whole thing will make a little more sense. So this is facing my left right now. But on the same token, there are things that I may want to put in the background that will be over my right shoulder here.

So I think you're starting to get the idea that there are a lot of things you can do with chromakey. And now we should have enough video footage for us to go in and start working inside where it's warm and doing our computer magic. So without further ado, see you later, bye.

Thanks for watching, hope you enjoyed it. I'm Tom Benford of Tom Benford Films Digital Video Productions, and if you'd like to read our step-by –step process for this tutorial, see the September 2008 issue of Videomaker, or you can go online to www.videomaker.com and search Record Number 13-749. You could also find out more on special effects at the Videomaker forums in Find. See you next time.

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