Tips & Tutorials

BCC Chroma Keying Workflow in Avid Media Composer

Published on: Sat, Jun 13 2009

Achieving a convincing chroma key composite is more than just slapping in a background and keying a foreground. It requires the use of integration techniques to marry the image elements together to give the impression they were shot with the same camera at the same time. This five-part tutorial demonstrates how to build a chroma key composite using Boris Continuum Complete (BCC) AVX plug-ins inside Avid Media Composer. Compositing tips will be shared and you will see just how easy it is to nest and pass a matte to multiple BCC effects in your segment. The end result will be a seamless composite.

Filters covered:

• BCC Chroma Key
• BCC Matte Choker
• BCC HSL (Hue-Saturation-Lightness)
• BCC Lightwrap


Click the videos below to play the tutorial. A full text transcription is included below each video.


Part 1:



First, let’s take a look at our clips. Our foreground is a toddler in a frog suit. He is in our V2 track. We’ll be compositing him over a tiled wall background in the V1 track.

Let’s begin by going to the Effect Palette. Inside the BCC Keys and Matte category we’ll drag the BCC Chroma Key icon to the foreground track of our multi-layer segment in the timeline.

Enter Effect Mode

Notice the foreground is already keyed - that was easy wasn’t it? That’s because our key color is set to blue at default. That’s okay, but we want to be more precise than that. So, we’ll sample our blue from the bluescreen.

Pulling the Key

The first thing we want to do, is click the Bypass button, which is located at the top of the Effect Editor controls. This will turn off the effect so we can see our bluescreen again.

To sample the color, let’s go down to the Color control, which contains a color palette and an eyedropper tool. Hover over the color swatch until it turns into an eyedropper, grab it, and drag it up to the Effect Preview Monitor. We're going to sample the blue closest to the boy's hairline - since the face will be the focal point, we want that area to be keyed well.

We’ll go back to our controls and click Bypass again, and there is our composite in progress. In case you’re curious and you want to view the matte we just created, set the output to Show Matte. This will help you see any problems in the matte that you may have missed when in Output Composite mode. You can see that the white foreground is opaque and the black background is transparent, which means we’ve pulled a pretty good key. If that isn't the case with your key, BCC Chroma Key offers several tools to help you clean up, adjust, and nail that perfect key. Those parameters are explained in detail in the BCC Chroma Key help document, which can be launched by pressing the Filter Help button near the top of the Effect Controls. By the way, all BCC filters contain their own help docs, which can be accessed by pressing that button.


Part 2:


Spill Removal

Now that we keyed our foreground and established a pretty good matte, the next thing we want to do is remove any blue spill that might be reflecting from the blue backing onto our foreground subject. Change the output menu back to composite.

Why don’t we zoom in a little bit here so we can get a closer look at our toddler. You can see some blue spill on the edges of the frog suit. Now, we can reduce that spill by lowering the Spill Ratio control, which is located in the Spill Suppression group. It’s important to make small adjustments here though, as you may end up turning your foreground subject yellow.

Here’s a tip when correcting blue spill on people – always look at the face. If they are looking a bit jaundiced as a result of a previous adjustment, take the Tone Mix control down a little bit to bring back a healthier looking flesh tone to your subject.

Fixing a Problem Matte

Most often the case, you’ll have a first-pass matte that has unwanted holes in areas that should be opaque. Adjusting parameters like the Density control in BCC Chroma Key can help fix that, but doing so, can also “fatten” the matte resulting in a degraded edge or Matte Line around your foreground. To fix this problem, we’re going to add a BCC Matte Choker filter.

Before we add the Matte Choker effect, let's untwirl the Title Matte parameter group in the BCC Chroma Key controls and select Multifilter Start. You'll notice the bluescreen suddenly appear - that is normal. This action will allow us to nest this segment and add more filters.

Inside the Effect Palette, navigate to the BCC Keys and Matte category and Alt-drag the BCC Matte Choker filter and drop it on the foreground track.

Now, let's untwirl the Title Matte parameter group inside the Matte Choker controls and select Multifilter End. We now have a BCC nested effect.

Inside the Nest

Here is a diagram that shows our BCC Nest within our segment. Our background tile wall is here in the V1 track, and our foreground toddler is in the V2 track. Also in the V2 track, are the BCC Effects we’ve applied so far: Chroma Key and Matte Choker. Since we only have two effects right now, Avid assumes it is a first and last effect. That is why we set our filters to Multifilter Start and Multifilter End. As we add more filters to the nest, those settings will need to change, as I’ll explain later.

Getting back to our matte problem that we’re going to try to fix with BCC Matte Choker.
At default, it looks like the values are doing their job a little bit too well. So, let’s lower the Blur 1 control, and Choke 1 control slightly, and that should give us a nice looking edge with no matte line.


Part 3:


Color Balancing

The next aspect of our composite to think about - is color. Does the foreground fit into the background colorwise? Almost. So, we need to add another filter.

Before we do that, let’s go to the BCC Matte Choker controls in the Title Matte parameter group and select the Multifilter Mid checkbox. Once you select Multifilter Mid, the image no longer displays composited over the background. For this reason, while you adjust your middle filters, it helps to select the Multifilter End checkbox so you can see the result as it should be seen. Then when you're finished adjusting, select Multifilter Mid again and your nest is ready for a new filter.

Inside the Effect Palette, if you navigate to the BCC Colors and Blurs category, you’ll see a bunch of color filters available at our disposal. Each one has their place, but the one that will best serve us right now will be the BCC Hue-Saturation-Lightness, or HSL effect. Alt-drag that filter onto our foreground V2 track.

Whenever we do color balancing, it’s always a good idea to see the foreground composited over the background because that’s what we’re color matching to. So, let’s go to the Effect Editor, inside the Title Matte parameter group and set Multifilter to End so we can see it over the background.

Whoa. That frog suit just jumps off that background; so, we should desaturate it a bit. Let’s go to the Saturation control and lower that. That looks better. Always remember to look at the flesh tones, and our toddler is looking a little magenta, so we’ll shift the Hue on him a bit. There we go.


Part 4:


Making it Seamless

Next, we're going to add one of my favorite BCC effects, the BCC Light Wrap filter. I really like this effect because it adds to the realism of a composite by creating an edge matte that allows the background image to be reflected around the border of the foreground image – and this results in a very seamless composite.

As always, before adding a new filter, we need to go into the existing filter and inside the Title Matte parameter group, select Multifilter Mid. Now we’re ready to add BCC Light Wrap. So, let’s go to the Effect Palette, inside the Keys and Matte category, and Alt-drag the BCC Light Wrap filter and drop it on the foreground V2 track.

Inside the Effect Editor, let’s untwirl the Title Matte parameter group of the Light Wrap controls and select Multifilter End. Since this is the last filter we’re going to use in our nest, we can just keep it set to End.

How does all that look inside our nest? From the bottom of the nest, we can see the first effect we applied – BCC Chroma Key. Then on top of that, we stacked our middle filters – BCC Matte Choker and BCC HSL, both set to Multifilter Mid. And, the icing on the cake, our last filter, is BCC Light Wrap set to Multifilter End.

Getting back to the Light Wrap effect, it should be working right at default. To see that, let’s change the View menu to Wrap On Black and you’ll see the edge matte that was just created.

Let's change the view back to Normal and go back to the controls. I'm going to back off a bit on the wrap effect because the hands are looking a little muddied. Go to the Width control and bring that value down slightly while we watch the hands.

Change the View back to Wrap On Black, we have less of an effect applied, we can see it right there, and then we’ll change the view back to Normal.


Part 5:


A Last Detail

For a final touch we’re going to add a drop shadow to our toddler. We could use the BCC Drop Shadow filter located inside the BCC Effects category, but why would we? All of the BCC keying and matte filters contain drop shadow capability that conveniently allows us to add a shadow effect during any of our matte-key processes. So, with that in mind, lets go to the Effect Editor and scroll down to the bottom of the BCC Light Wrap controls where we’ll see a Drop Shadow parameter group. Untwirl it and select Enable Drop Shadow. Right out of the box the drop shadow looks pretty good, so no need for adjustment.

And, there’s our composite showing all of the nested effects applied. We achieved our goal of getting the foreground to fit into that background environment. But don’t stop here! Feel free to experiment and add more BCC filters to your nest. For example, if your blue or green screen was shot using a Red One HD camera, but your background was shot on 35 millimeter film, add a BCC Match Grain filter to your nest to add grain to your clean Red footage.

That’s just one of many solutions BCC can offer you, the Avid Editor. This has been John Lafauce for Avid Technology.


BCC filters come bundled with Avid Media Composer, Avid Newscutter and Avid Symphony.


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