One of the most powerful techniques for combining multiple layers of video into an output is the use of masking, also known as luma keying. With this process, two video sources are combined to create a "cut out" layer that can be composited over others image like a collage instead of simply blending them together. This style is commonly found in music videos, graphic design, and by VJs for live performance. Masking is also an important technique used when projection mapping video onto surfaces.