Final Cut Studio 2: Chroma Keying
Chroma key, also called bluescreen or greenscreen, is the magical process that inserts an image seamlessly onto an entirely different background. Getting the edges of the subject perfect means the difference between a convincing key and obvious chicanery. In Final Cut Studio 2: Chroma Keying, Larry Jordan focuses exclusively on this effect, so a general knowledge of Final Cut Pro and Motion is recommended. He demonstrates the strengths and weaknesses of five different keying tools: Final Cut Pro's native keyer, Motion's Primatte RT, Oak Street Software's vKey2, dvGarage's dvMatte Blast and dvMatte Pro, and Red Giant Software's Primatte Keyer Pro 4.0. Each excels in different areas, so Larry explains typical issues and workarounds, and when to consider using a different application. Example files accompany the course.
- Understanding how the production process affects the quality of the final key
- Fixing focus, lighting, and color issues
- Removing unwanted items in a frame using garbage mattes
- Removing green edges and stair-stepping
- Retaining or removing background shadows
- Handling motion blur and interlacing
Welcome/Production considerations/What is covered?
- Hi, my name is Larry Jordan, and welcome to this session on doing Chroma Key inside Final Cut Studio. Now you may look around and you're going to say this is not Final Cut Studio, this is actually a set. Because Chroma Key starts on the set, it doesn't start in the software. And I've enlisted the help of the ever-beautiful Megan to illustrate two things about lighting inside Chroma Key. Because Chroma Key actually has two different lighting zones. It's got lighting for the talent, and it's got lighting for the green screen. I want to talk about both of those, talk about some other physical setup that you should consider as you're doing your own green screen work.
Then we'll shift gears into the software. So let's talk lights first. Megan is lit with a key light which is about 30 degrees over from the camera, and about 30 degrees up. It happens to be a fluorescent soft light that we're working with, and it's about, oh, I'd say about five feet away from her face. Notice how it brightly illuminates this side of her face giving us some shadows on this side of her face. Now we're filling in those shadows with a fill light. It's about a three-and-a-half-foot square fill light. It's about 12 to 15 feet away, and because it's so much farther away, the fill light is not as bright as the key light.
Because of this difference, we're getting this modeling, the shadowing on her face. Now this is appropriate when you want to have something that is dramatic or serious. And also guys can tend to be lit with darker shadows than women can. But if you want it to be romantic, and you want it to be soft, or not in the case of Megan, if you want to bring someone in on the older side of young and make them look like they're on the younger side of old, you want to bring your soft lights in, bring them closer to the lens of the camera, and you want to have it be about the same level as the camera lens. Or, we can add what's called a reflector.
A reflector is a piece of fabric, some of them are professionally made, but, notice how as I add the reflector, notice as it picks up the reflection from that key light, it's filling in these shadows and making them less dense. The benefit to a reflector is it doesn't generate heat, doesn't take power, and you can adjust the angle of the reflector to fill in these shadows to soften the look of the face. Now, in addition to the key light and the fill light, we also have a back light. The back light allows us to illuminate the hair, and notice that as she moves her hair, it picks up the back light to give a sense of dimensionality.
Also, it adds light rounding the curves of her shoulders. To separate her from the background. The benefit of the back light is to provide a separation inside a standard def picture, which is just two dimensions, height and width. This back light provides dimensionality. But in addition to the key, the fill, the back light, and Megan, we also have to light our green screen. This green screen is fabric, it's stretched between two C stands, and it uses these stage clamps. The benefit to using a stage clamp is that we can pull that green screen really tight, clamp it in because our goal is to get these wrinkles, these shadow areas as stretched flat as possible.
And we'll have some more techniques I'll talk about in just a minute. Ideally, the best green screen is painted because you paint it on a flat surface, there's no wrinkles at all. But in our particular case, because this is a temporary green screen, we'll just stretch it on these C stands and pull it apart. Stretch it out so that it's as flat as possible. The next is to light the green screen. And that involves these set lights. Now there's two schools of thought on how we want to do green screen lights. We can use soft lights and we can use what I call hard lights. Here's a soft light, it's a Lowel Rifa light, and the nice thing about a soft light, it gives us a big, wide light that shines evenly out from the instrument itself.
The problem is, it only shines about four, maybe five feet. Soft lights don't project light very far. They're very good for giving us a wide light that wraps around the face of the talent. But, I am of two minds about whether they're really good to be used for green screen work. And, you can make your own decision on whether you want to use them or not. The nice thing is it's very smooth, but it tends to be kind of dim. If you need something where the lights are farther back from the green screen, you want to work with a harder light, like this par light from Arii. It's a 650 watt light. Much brighter, much more heat, but it could be farther back and we can open it out so that it gives us a nice, even light across the green screen.
We got a couple scrims in here to knock the brightness back just a little bit. The benefit to these is the greater distance that you get. They don't have to be quite as close to the green screen because avoiding shadows is the absolute number one thing you want. You want to have the green screen be as flat, as smooth as possible. And, look at where the chair is. The chair is not next to the green screen. If I hold my hand up, I can't hit the green screen. In fact, look at how far it is. It's almost 10 feet away from the green screen all the way up to the chair.
And the reason is now I've got a clear zone where I light the green screen, and I've got a clear zone where I light the talent. You want to have between eight and 10 feet of distance between the talent and the green screen to make sure you've got good separation between talent lighting and green screen lighting. But equally important is the separation between the talent and the camera. Now, this gets tricky, watch this. Look at the distance between the chair and the camera. I've got a 10-foot distance.
The benefit to this is that when you've got a good distance between the camera and the talent, the camera has to zoom in. The more it zooms in, the shallower the depth of gets. The shallower the depth of field, the more out of focus the green screen gets. The more out of focus the green screen gets, the softer it gets. So in addition to stretching it tight to get rid of as many wrinkles as you can, in addition to lighting it flat, to hide the wrinkles that are there, then you de-focus the background by zooming in, suddenly that green screen becomes just a mass of soft green, which makes it very, very easy to key.
So with that as an introduction to the production considerations in Chroma Keying, let me share with you what the rest of our title is going to cover. Next, we'll take a look at Chroma Keying inside Final Cut Pro, what filters you need, and how to use them. Then, there's an entirely different way that we can key inside Motion, and I'll show you how that works, plus, I'll show you how we can move projects back and forth between Final Cut Pro and Motion. But it's also important to know that there is no one perfect keyer. So we'll take a look at three third-party chroma keyers, Oak Street Software's vKey2f, dvGarage's dvMatte Blast, and dvMatte Pro, and Red Giant Software's Primatte Keyer Pro 4 to explain sort of the differences between these different keyers and why you might want to choose one versus another.
Finally, we'll spend the bulk of our time dealing with special issues. We'll start by an overview of how to work with filters in Final Cut Pro and then solving problem video. Everything from dark and messed up backgrounds to talent that's out of position. And we'll wrap up with some tips for color correction that can improve the look of your keys. There's a lot to cover, and I can't wait to get started. So we will, in the next movie.
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