Final Cut Studio 2: Chroma Keying
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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 are 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 have 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 zones 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 setups that you should consider as you are doing your own green screen work and will 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 degree up. It happens to be a fluorescent soft light that we are working with and it's about - I would 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 the face. Now we are filling in those shadows with the fill light. So about a three-and-a-half foot square fill light, it's about 12-15 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 are 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 content 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 are on the younger side of old, you want to bring your soft lights in, bring them close to the lens of the camera and you want to have it about the same level as the cameraman's or we can add what's called the 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 the shadows and make 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 of 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 that 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 a back light is to provide a separation inside a standard depth picture, which is just two dimensions, height and width. This back light provides dimensionality. But in addition to the key, the fill and 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, the shadow areas as stretched flat as possible and we will have some more techniques I will talk about it just a minute.
Ideally the best green screen is painted because you painted on the flat surface, there is no wrinkles at all, but in our particular case because this is a temporary green screen, we will just stretch it on the 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 are two schools of thought how we want to do green screen lights, we can use soft lights and we can use what I called the hard lights. Here is a soft light, it is 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 five maybe five feet. Soft lights don't project light very far.
They are very good for giving us a wide light that wraps around the face of the talent but I am of two minds about minds about whether they are 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 Arri. It's a 650 watt light, much brighter, much more heat. But it can be farther back and we can open it out, so that it gives us a nice even light across the green screen. We have got a couple of screens in here to knock the brightness back just a little bit.
The benefit to this 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. 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 ten feet away from the green screen all the way up to the chair and the reason is now I have got a clear zone where I light the green screen and I have got a clear zone where I light the talent. You want to have between 8-10 feet of distance between the talent and the green screen to make sure you have got good separation between the 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 have got a ten foot distance. The benefit to this is that when you 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 field 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 soft it gets. So in addition to stretching it tight to get rid of these wrinkles as you can, in addition to lighting it flat to hide the wrinkles that is there, then you defocus the background by zooming in, suddenly that green screen becomes just a massive 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 will take a look at Chroma Keying inside Final Cut Pro, what filters you need and how to use them. Then there is an entirely different way that we can key inside Motion and I will show you how that works plus I will show 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 will 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 4.0 to explain sort of the differences between these different keyers and why you might want to choose one versus another. Finally we will spend the bulk of our time dealing with special issues.
We will start by an overview of how to work with filters in Final Cut Pro and then solving problem video, every thing from darkened, messed up backgrounds to talent that's out of position and we will wrap up with some tips for color correction that can improve the look of your keys. There is a lot to cover and I can't wait to get started, so we will in the next movie.
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