g on green or blue screen allows filmmakers to create impossible effects. It allows teachers to use standard off-the-shelf applications (Fireworks, for example) to combine graphic information from a variety of sources.
The subject can be shot on camera and then placed in an entirely different background scene. "Chroma" refers to the purity, brilliance or richness of a color, and the “key” refers to cutting a “keyhole” or outlined image. Blue and green are the primary colors used as backgrounds because those are the least likely human skin tones.
Teachers can use chroma keying through Adobe Photoshop or Fireworks, as we have done in class. In this case, the digital image, shot against a green screen, can be extracted from the green background. This is done with a pixel range isolation tool like the Magic Wand.
First, a reference green space is selected with the tool. Then a range of shades of green, represented by pixel values, is selected above and below the reference value. Once the range is selected, pixels in that range can be subtracted from the image to eliminate the green background and isolate the subject. The subject image may now be imported to and combined with other images as a new layer. See below for an example - I don't have a beach house in Malibu, unfortunately:
To chroma-key, download photos to your desktop, crop your images so only the main image and the background show, then open them in Fireworks (Mac):
1. Highlight the Magic Wand Tool.
5. Copy and paste desired image into background image and resize appropriately.
6. If you do not want to copy and paste the background photo, click on File then Import and select the desired photo from the screen that pops up.
7. A sideways L will appear, click and drag it to cover your extracted picture. The picture should appear.
8. To bring the extracted photo in the front of the background, go to the left side layering window and move the extracted photo before the background photo in that window.
9. Save as a png file if you want to make changes later. If you want to save memory, save as a jpeg, but the photos will be recognized as a single file.
Read more: The History of Chroma Keying | eHow.com
Read more: The History of Chroma Keying 2 | eHow.com
Read more: Chroma Key at Wikipedia