How Does a Green Screen Work: The Ultimate Guide


For many decades now, movie goers have been aware of the power that green screen effects bring to a video production. Actually, in the early days a blue screen was more common. But the overall technique of chroma keying has been known for a long time. Only relatively recently, however, has the technology been available to let the average user take advantage of these powerful effects right from their home. In this post, we'll tell you all about blue screens, green screens, and chroma keys. 

Is there a difference between green screen and chroma key?

What is a green screen and what is chroma key? Are they the same? The answer is mostly yes. Technically, green screen refers to the equipment used to perform chroma keying. Though the noun phrase “green screen” is often used interchangeably as a verb that means the same thing as chroma keying. Chroma keying needn't use a green screen though. The act of chroma keying is removing a certain color from a video frame, so that something else can be placed there. Usually, this is used to remove the background and put a character in another location.

How does a green screen work?

With modern software, the magic of green screen is easy to understand. If you have an evenly lit green screen behind your actor, you can simply load the footage into your favorite video editor, tell it to turn anything in the shot that's green into a transparent color, and then overlay that video footage onto a new background. Getting the best results requires a fair amount of planning and extra work though. Let's take a look.

Choosing a screen color

The common screen color is a lime green hue. This isn't always the best color to use, however. An obvious example is if your character is green, or is wearing a green outfit. Now, your chroma key software will remove them as well! Another example is the target background. For example, if you want a character flying through the sky, a blue screen may be better. That way, any blue that isn't keyed out still matches with the background. 

Lighting for chroma key

As mentioned earlier, whatever color the screen is, it should be evenly lit. It should also be lit very distinctly from the foreground elements that you wish to keep. Lighting the screen in this way maximizes the contrast between it and the foreground elements, making it easier to separate the two. Even lighting reduces shadows, and reduces the number of shades that the chroma key software needs to key out. 

Keying out the screen

Most video software has chroma key functionality built into it. There are also some very pricey chroma key plugins that are designed to take a lot of the guesswork out of the process for you. Even without these plugins, it's just a matter of tweaking the values until you get something you like. In general, you will choose a color and then adjust a threshold around that color. The more evenly lit your screen is, the lower the threshold can be, reducing the chance of cutting out elements you'd rather keep.

Improving the composite

Typically, after a chroma key, you'll want to perform some additional post-processing to help the foreground blend with its new background. A common technique is to very slightly blur the edges. This will aid in reducing the sharp lines that are a dead giveaway that chroma keying was used. Another common thing to do is to adjust the color levels so the lighting of the two shots matches more accurately. 

Conclusion

If you're looking for quality video editing software with support for chroma key functionality for your next green screen project, consider Roxio Creator. It's easy to use, and will also allow you to burn videos to disc, convert to and from a wide variety of formats, and easily share your creations. 

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