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ChromaKey - BlueScreen - GreenScreen - All the Same Thing!

by Bob Saskins

Ok first things first...what the hell is Chromakey ..bluescreen etc. Well firstly they are all basically the same thing. Think of the weather forecast on TV. The guy / gal standing in front of a giant map of "whatever country you're living in"  with overlays of storm fronts, clouds rain..whatever. This effect is achieved by using Chromakeying.

 

special fx bluescreen chromakey

So in other words chromakeying is the process of filming a scene, object or person in front of a pure coloured screen (typically either blue or green) so that the colour can be removed later to be replaced with a scene or to achieve certain special effects. The majority of  motion pictures use at least some blue-screen effects ( chromakey ) during production so chances are you may find a use for it in your own animations as well. Remember those old Superman movies, (wow this guy can fly)  nope his SFX production team knew how to use chromakey. Christopher Reeve (RIP) spent a lot of time dangling from wires in front of a bluescreen backdrop. The blue screen was then replaced with live footage of moving clouds, flyby's and so on. But you may also remember from those days (if you are as old as I am) that there always seemed be a shimmer or halo around the flying figure of superman. Well that's now become a thing of the past as technology has improved the precision of chromakeying. Now modern movies such as the the more recent Star Wars Trilogy and a whole host of sci fi TV programs and movies have used bluescreen chromakey to bring characters in to outer space and alien worlds.

By using  blue-screen ( chromakey ) you will be able to provide a backdrop for your animation character when it may be impractical to actually film in the desired location. So if you want your characters to be standing next to a river or a lake for example  you may choose to find some lake or river footage and then film your characters in front of a blue-screen. Using any number of stop motion animation software packages  you can then remove the blue and replace it with the river or lake footage.

So you want to use it in your stop motion animations. Hmm! It's it easy? Well yes and no.

Green or Blue ...which is for you?

Well green is more popular these days as it is better suited to digital cameras (debatable  go debate ) and is easier to light. As a point of interest the early Superman movies used blue screens but in Superman returns went to a green screen. Go figure! But seriously the Superman blue suit had more to do with the change over. And that brings me to an important point. Your characters color of clothing or skin tone. Yes you are more likely to have blue or maybe even green animation character when using clay for example and therefore will want to avoid having your character and backdrop of a similar color. Right! So think of this when choosing green or blue screen.

 

Lighting you backdrop.

As always with any stop motion animation, filming lighting is critical. It is just as important to light your backdrop correctly. And that means evenly lighting the entire screen. Avoid hotspots of intense light as they will cause problems when chromakeying in postproduction. Many programs use a tool which looks something like an eyedropper icon (similar to those in digital photography programs such as Photoshop, Gimp or Paint.net ) to select the shade of green or blue in the backdrop and key it out. The result will be far better if you have an evenly lit backdrop.

 

Placing your Characters for Animation.

Shadows and light spill. You will want to avoid these. It is better to stand the subject as far away from the backdrop as possible to separate the two. This will reduce spillover from the lights illuminating the character into the lighting on the green screen. It also helps to blur the backdrop somewhat as it is slightly out of focus compared to your characters, which keeps wrinkling and other blemishes from affecting the chromakey effect.

 

Filming

Ok so now you have your lighting right and your animation is ready to shoot. If you are using a still image or a moving image for your movie you will be relying on  your stop motion animation package / program to adjust what is called "tolerance". With your image loaded you will use a color picker tool to choose the color "green" or "blue" near to your characters outline to get the best keying or match for the chrTypical Tolerance Adjustment for Chromakeyomakey effect. Moving the tolerance slider increases or decreases the color replacement with your choosen green screen image.

 

Once you have shot the footage in front of the green screen, it's time to composite it, via your favourite stop motion animation editing program. How accurate the compositing looks will depend on the quality and accuracy  of the stop motion animation program you use. Its quality will  help to reduce or eliminate that green-screen halo effect. Most non professional stop motion animation packages do a reasonably good job of chromakey. If you want near perfection then you will have to pay 100's of dollars (up to $1,000 for Adobe After Effects ) for example.

A Convincing Digital Background
 

If you don't have movie footage (normally in the form of AVI files) to hand then there are several companies that sell slick-looking video backing tracks which you can loop to form a digital background, so you can green-screen the animated characters in front of it. Combining these clips with a DV camera or a high end Webcam a few carefully choosen lights and stop motion animation software with half decent chromakey makes it possible to turn virtually any bedroom or garage into a video or movie studio.


Of course, these virtual sets aren't for everyone: they may be too much hassle or expense for a production that will
ultimately end up as a five-minute clip on YouTube. A less complex backing may be more appropriate for some productions;
obviously, experimentation is the key.
 


This article only touches on what chromakey and green screen is capable of doing. Your animations may not make Spielberg or Aardman studios pick up the phone but  you might  be able to elevate the quality of your next YouTube clip with a bit of experimentation.! Good Luck with it!


 

About the Author

Bob Saskins works as a freelance video production assistant in LA. He is a keen animator and LA dodgers fan!

Copyright for this Article - Bob SaskinsĀ©


 
   
 

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