Color keyer
The Color Keyer effect uses the same principle as the Luma Keyer effect. It deletes the selected color on the image or video footage of your choice. It is no longer required to concentrate on pixel luminosity but on the entire color.
Two types of parameters may be locked with a keyframe: Tolerance and Softness. In the FX stack above we see: the higher the value of the Tolerance parameter, the more colors close to "blue" will be deleted. The higher the value of the Softness parameter, the less abrupt the transition between opaque and transparent pixels will be.
The image below shows that most of the bluish colors of the sky and cloud have turned transparent:
The green and dark colors of the tree are further away from blue and therefore opaque.
With the Invert parameter, the effect can keep the color chosen in the Color parameter whereas to remove it.
The image below shows the effect of the Invert setting when checked:
These two keying effects may, of course, by applied to a complete footage, which makes work easier when using a scanner with loader or a recorded video sequence.