ABSTRACT
Keying is the process of building a matte (alpha) based on the chroma or luma properties of an image for the purpose of compositing. Keyers use algorithms to isolate pixels of an image and assign those pixels to black, white or a gradient value for the alpha based on user-defined settings. Advanced keyers have multiple algorithms for analysing pixels in several different modes, such as RGB, YCrCb, HLS and Luma. Some keyers also have colour correction tools for suppressing or hue shifting colours. Colour suppression and hue shifting is an effective way to remove unwanted colour spill on the foreground image. The keyer in fire is integrated directly into the DVE module, meaning multiple layers can be keyed and composited simultaneously. In the example shown in Figures 4.6.6-4.6.8, a model plane was prepared on bluescreen; fire’s keyer was used to build the alpha for this image and replace the background with the sky image as the new background.
