Chroma-key refers to the practice of photographing a foreground image against a solid background. The solid background is then selected and removed, leaving the image with a transparent background. The foreground image with the transparent background is then overlaid on a new background to create an image with an object that appears to be in a place where the object never really was.
Chroma-Key Screens
The easiest way to create a chroma-key image is to use either a blue screen or a green screen as a background. The size of the background will depend on the size of the object being photographed. For example, if a small model of a motorcycle is being photographed, a small chroma-key background will work. If a full-sized car is being photographed, the size of the background will have to not only accommodate the larger size of the car, but will have to accommodate the angle of the photograph and the visual size of the background from that angle.
Although chroma-key backgrounds are easier to work with, with digital compositing techniques via programs such as Photoshop, any solid-colored background can be used as a background. Chroma-key backgrounds tend to be an unnatural color and, thus, are easier to select in a digital compositing system.
When shooting a chroma-key image, it is important to have even lighting to ensure the background is smooth and consistent.
Removing the Colored Background
To remove the background, select the background colors based on a luminance channel. Once the background has been selected and the selection marquee contains only the object to be placed in the foreground, the background image can be deleted and the background image layer can be set to transparent.
Compositing the Image
To create the composite image, the foreground image with the transparent background is overlaid on a new background. In most cases, the transition edge between the foreground and the new background will be too sharp to appear natural. Softening the transition usually fixes this. Often, the resulting image is impossible to distinguish from an image where the foreground image was photographed at the same location as the background.
Tags: background will, foreground image, image with, being photographed, image with transparent, size background