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We've all seen the tutorials that show you a one click process to pull a beautiful key. But many times, the lighting for the green screen shot you're working with isn't lit perfectly, and has objects in the shot that you don't want. In this segment, we show you how to remove unwanted objects from your footage, and key out a background with uneven lighting. Knowing how to fix these issues is the staring point to pulling a great key, even when the footage presents a challenge.
Every green screen setup is a little bit different. From the lighting, to the subject, to the type of camera the footage is shot on, there are many factors that contribute to the ease or difficulty of pulling a good key. It's important to note that the steps covered here are only the beginning, and that subsequent steps will be covered in future segments.
Let's start by looking at this footage shot in our studio. We've intentionally lit the green wall to have some bright and dark spots and even left some wrinkles in the fabric. There's also some unwanted items in our shot, and some unnecessary green area around our subject. These are common issues when dealing with green screen footage.
The first step to getting our footage properly keyed is to remove the unwanted objects in our scene, as well as the green area that doesn't contain our subject. We can achieve this using garbage mattes in premiere, and masks in after effects. Let's start in premiere.
Under the keying effects, you'll find a four point, eight point, and sixteen point garbage matte. In this case, we'll use the eight point matte. Apply the matte to your clip and simply pull the points in until you've got a reasonably tight mask around your subject. Be sure to scrub through your footage to ensure your subject doesn't extend beyond the mask. You can see, just by using a simple garbage matte, we've already eliminated some issues in our background without even pulling a key.
You can achieve the same effect by using a mask in after effects.
Select your clip on the timeline, then select the pen tool. Now draw your mask point by point around your subject area. Be sure to close out the mask by joining your final point with the first point. If you need to remove a point, move the pen tool over an existing point until you see the minus symbol and click. If you need to add a point simply hover over the mask edge until the plus sign appears and click. To adjust existing points on your mask, use the selection tool and simply click on a point and drag it.
So the excess area in your clip is removed, and now it's time to pull the initial key. The goal of this step is to make the green background transparent, and your foreground fully opaque. It's okay to have a bit of transparency around the edges and hair. We'll show you how to pull an initial key using chroma key in premiere pro, Ultra in premiere pro, and keylight in after effects.
Using these 3 different techniques will cover a range of approaches that will be useful in any edit program. While the more complex keying effects offer flexibility and fine-tuning controls for better results, some programs only include a basic keyer without a lot of bells and whistles. These effects can return some pretty rough results, and we'll demonstrate one of these simplified effects using the chroma key effect in premiere pro.
First we'll apply the effect to our clip. Using the eyedropper, we select a point on the green screen as close the talent as possible. Theoretically, if our lighting was perfect, our entire screen would key out, but as you can see, the uneven lighting has given us a bit of a challenge. Most keying effects will have various view options. In this case, checking the mask only box will show us the clips alpha channel. In this view, the black areas are completely transparent, the white areas are completely opaque, and the grey areas have varying degrees of transparency. It's clear that we'll need to make some adjustments to get a better key. The similarity control will broaden the range of the target color. Raising the value will help us key out the varying shades of green. We're having to raise this pretty high due to the background being unevenly lit. This looks pretty good in the alpha, now lets uncheck the box and see what our key looks like. You can see that the basic key looks good, but we'll need to work on the edges in the next segment.
While the chroma key effect isn't the ideal tool, you can still achieve a rough key, even without proper lighting. Now let's look at another effect we can use with a little more control.
In premier pro, we'll apply the ultra key effect to the same unevenly lit footage. Using the eyedropper, we'll select a point on the screen that's close to our subject. Changing the output view to alpha channel will show us the varying degrees of transparency, and you can see we've got some work to do. Using the matte generation tools can help us adjust the key to get a better result. Because of the uneven lighting, we'll have to start with some major changes in our pedestal. Once we have a good portion of the background out, we can now fine tune by by adjusting the shadow and highlight parameters. Raising the shadow parameter will increase the opacity of the dark areas of your image, lowering it, will reduce the opacity. In this case, we're trying to get these areas of the green screen to be completely transparent, so we'll lower the shadows. It's important to note that when dealing with green screen, we always want to make the smallest adjustments possible in order to prevent the creation of more issues. Lowering the highlight parameter will get rid of the hotspot on our wall. Notice that by getting rid of the green, we've lost some opacity in the jeans area. We can used the transparency parameter to help restore it. Lowering the transparency restores some opacity in our foreground. By going back to the composite view, you can see that this initial key, even with some issues in our footage, is on it's way to looking good. We'll do some fine tuning around the edges in our next segment.
A third option we'll demonstrate is the Keylight Effect in After Effects CS5. This is a powerful option to pull great keys.
Using the same footage, we apply the effect to our clip. In this case, we use the eyedropper to select the screen color, again picking a point close to the subject. Changing your view to status will give an exaggerated view of the alpha channel. In this view, black is transparent, white is opaque, and anything that's gray is partially transparent. This view is a great tool to show you all of your matte issues, including the minor ones. The best way to clean up your initial key is to use the clip black and clip white controls, which are found in the screen matte controls. Adjusting the clip black parameter will help eliminate the areas of green screen that haven't been fully keyed out. Adjusting the clip white levels will help restore opacity to the areas of your subject that are unintentionally being keyed out. It's important to make the smallest adjustments possible to clean up your key. Be sure to check a few different points in your clip, and view it in motion to check the key. Switching the view back to final result will show that this initial key looks pretty good, and we'll clean up the edges in our next segment.
Knowing how to get rid of unwanted objects and pulling a good initial key with uneven lighting is just the first step in fixing your green screen problems. In our next segment we'll show you how to fix the rough and discolored edges of your subject. Correcting these issues is an important step in the keying process. And it's one more crucial component that can really help your green screen work shine.