In computer graphics, what is alpha compositing?

In computer graphics, what is alpha compositing?

• Removing unused image information from a layer and use it to enhance another one (8bit to 16bit)
• Combining an image with a background to create the appearance of partial or full transparency
• Combining images to achieve pseudo 3D look
• Removing a range of colors in RGB from an image for a stylized look

EXPLANATION

Alpha compositing is the process of combining an image with a background to create the appearance of partial or full transparency. 

It is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image called the composite.

 For example, compositing is used extensively when combining computer-rendered image elements with live footage.