In the 2006 movie, Pirates of the Carribean II: Dead Man's Chest, Davy Jones is the sinister villain who looks like a half human, half octopus hybrid.

He has no mercy...he has no heart...and he has no problem keeping his tentacle beard looking well-groomed and salon fresh in the face of Captain Jack Sparrow's threats. How does a barnacle-covered villain do it?

It's all thanks to blue screen technology.

Bluescreen technology is a major component of most modern special effects. The technique results in composite pictures or pictures made of separate images that are put together to generate one image. The composite images are the ones that we see on the big screen.

 

Did You Know?
It took a crew of 80 compositors to make Pirates of the Carribean II: Dead Man's Chest.

How are multiple images combined to give that final image? First, a subject (which can include actors or objects) is photographed or filmed in front of a background screen that is traditionally blue.

Despite the name, not all screens are that hue; in fact, they can be yellow,magenta, or green. One key requirement is that the screen must be apure colour which means that it's evenly lit — no shadows! Most importantly, there needs to be a high contrast that distinguishes the background from the objects that are being filmed.

Blue was traditionally used because older cameras and films were most sensitive to the colour blue, and it is not found in human skin. Nowadays, green is preferred because it requires less light and digital cameras retain more detail in the green channel.

Sometimes, filmmakers will also choose a color based on what they are filming. For example, you wouldn't want to film a bright blue bird on a blue background; after applying effects, the bird would disappear!

 

Did You Know?
It's unlikely that filmmakers will use a red screen because of the high levels of red in human skin.

In addition to a blue screen image, a photograph is also taken of the background. These original images are then altered to produce mattes or pictures with missing portions that will eventually be replaced.

The original photographs are photographed again using special coloured filters to generate negative images where an actor's silhouette is clear and the background is black. A positive image is then generated where the actor's silhouette is now black and the background is clear.

 

Did You Know?
The colour of the filters used depends on the color of the screen. If the screen is blue, a blue filter allows the background to be exposed to generate the negative image. A combination of red and green filters allows the actor to be exposed to create the positive image.

The original images are photographed again using the dark portions of the mattes to block out areas of the picture. The clear portions allow certain areas to be photographed resulting in two pictures: a perfect background picture with a blank space and a picture of an actor surrounded by nothing.

These pictures fit together like puzzle pieces and are eventually combined using projectors, cameras,and a beam splitter to form the final product.

 

Did You Know?
New technology allows the photographs to be scanned and digitally modified rather than taking new photos.

So,what about things that can't be filmed because they don't exist? That's where computer generated images come into play — the same technology that was used to make movies like Monsters Inc. and Shrek helped create the dangerous Kraken.

Whether a background or creature is photographed or digitally generated, the star in the process is the blue screen technology. The technique allows creators to make movie and TV magic by allowing ordinary actors to be transported to places under the sea or to defeat evil, undead pirates.

Learn More!

How Stuff Works: Blue screen technology

Wikipedia on Blue Screen Technology

Seanet on Blue screens

How to use bluescreen for your own footage. Click Here

Want to see the magic behind Pirates of the Caribbean? Look at the Lucas Films website to see how it was done

Photo Credit: Ultimatte

Alexandra Silveira is a graduate student at the University of Alabamaat Birmingham. She loves winter breaks, snow, and hot chocolate…with marshmallows.

Alexandra Silveira

I just received my PhD from the pathology department at the University of Alabama at Birmingham. I currently live in Providence, Rhode Island and co-manage the Entertainment section of CurioCity. In my spare time I read about science, watch horrible comedies, and am an aspiring Rock Band rock star.


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