green screen video for families

Chroma keying is a really useful skill to add to your effects creation tool set. The only trouble is that it is rather a black art. That is, keys are rarely achieved with precisely the same settings and it takes skill and practice to do it well. However, it helps to follow certain basic procedures to be successful at it on a consistent basis. As long as your image is shot and lit correctly, you're halfway there towards succeeding at a convincing chroma key effect. This article is written and designed for you to achieve predictable results in keying using the Chroma Keyer filter in Final Cut Pro HD.
If you weren't already aware, chroma keying is the process of electronically "cutting out" a subject shot against a solid colored blue or green screen. Once the subject (in our case, a woman named Linda) has been removed from the background, you are free to place it on an upper track, say V2. This allows you to place a different background behind the subject, which opens up new possibilities for creating visual effects.

When you are removing the blue or green areas of the backdrop, what you are really doing is creating an alpha channel, (or matte) which will create an area of transparency around your subject.

In this article, I'll be attempting to use the FCP Chroma Keyer on "Linda", which is one of the more difficult keying jobs that I have faced in the past few years. This was originally shot on Beta SP with a 3CCD camera that had a pro lens.

Sounds great, right? Not really. Although the source was of high quality, I found that Linda's shiny black outfit absorbed a good deal of spill from a set, which was strongly over lit. Also, Linda had 2 quick hand gestures, which made it difficult to maintain a good solid key for about 24 frames. Because of this, my key will need some troubleshooting, which will require some techniques that I'll share with you a bit later.

Let's get started, though, with the process of chroma keying a standard shot and I'll work along with you.

Creating a clean key begins before you even launch FCP. As I mentioned earlier, with chroma keying, you'll have to start with the highest possible quality video at the shoot. Perhaps, you have heard the phrase "garbage in=garbage out". This old adage really applies to chroma keying, as a higher quality clip will give you a smoother edge around your subject.

Although this article will not instruct you how to shoot for blue or green screen, I can offer up a few pointers. For more details, read the article by Charles Roberts entitled, "Chroma Key Basics for DV Guerillas Part 1". This will give you a broader view on this topic.

There are a few key points that I can share with you if you have any control over how the shoot is executed or are actually shooting it yourself.

* Use the highest quality camera and acquisition format possible (Ideally a 3CCD video camera). Use larger CCD chips, and quality lenses if possible. You can use miniDV or DVCAM, but your results will be notably improved by shooting with formats such as DVCPro 50, Digital Betacam or HDTV.

* Pay special attention to the lighting. The background should be lit as evenly and flatly as possible. Strive for no shadows or creases in the backdrop.

* Place your subject as far from the backdrop as possible, so they will not cast any shadows onto it. Another reason is so that the backdrop will not create "spill" (reflected green or blue light) onto the subject, making keying more difficult.

* Light your subject as you would like to see it in the final composite. Cut off this affected light from the backdrop with flags or foam core. In my opinion, this is the problem with the "Linda" shot. She was not separately lit apart from the backdrop.

* Make sure that your subject isn't wearing clothing or accessories that are the same color as the background.

* Smooth down any flyaway hair and avoid any fringe in the clothing. Avoid jewelry, like earrings and necklaces that might reflect blue or green or that might be difficult to key due to the relative size of the objects.

* Make sure that the talent is not wearing green if you are doing a green screen shot or blue if it is a blue screen shot. Black is also not a good choice since it tends to absorb spill. Note that Linda is wearing an outfit made of shiny, black material.

* Lock down the camera and do not move it during the shot, unless you know how to do motion tracking. Motion tracking is not available in the stock FCP package.

* Use a Green Screen is you are shooting video. Use a Blue Screen if you are shooting film or have a blonde haired subject. Either will work, however. If you have a non-human subject, you can use any color for the backdrop. A product shot with blue and green in it might need a different colored backdrop, like red.

After the shoot has wrapped and you have the footage in hand, you can begin to prepare it for keying. You'll first need to get it into Final Cut Pro at the best possible quality. Most people will probably be using miniDV or DVCAM. This used to be problematic because of the limited colorspace of 25 Megabit miniDV or DVCAM (which is sometimes referred to as 4:1:1 sampled footage), but now it is less of a headache with a new filter that was added to FCP 4, called Chroma Smoothing 4:1:1. If you have an opportunity to shoot the piece on a higher quality format, then by all means, do so. You'll get smoother edges around your subject when you begin to work on the key.

A new filter called Chroma Smoothing aids keys shot in 25 and 50 Megabit DV formats.

After the footage has been logged and captured into a bin, you can begin working on your chroma key effect. First, place any background footage onto V1 in the spot where you wish to start the effect. Then, edit the green screen shot directly over the V1 clip on V2. You should turn off the V1 clip temporarily so that you can work against the background of the Canvas. To do so, select the clip and type Control + B. In the Canvas, I switch off between the black, white and checkerboard backgrounds as I adjust a key. These choices are available in the View pop up menu. Leave it set to Black for now.