Over

Composites any foreground over any background using the matte in the foreground's alpha channel.

Requires a Background Input (RGB or RGBA) and a Foreground (RGBA).

Produces an Output (RGBA).

Composite

Opacity	Sets the opacity of the foreground element.
Foreground Type	Specifies whether the foreground clip is premultiplied, the clip is not premultiplied, the clip is on a specific backing color (which you can set using the Backing Color sliders), or the clip's backing color should be set automatically.
Backing Color	Set's the foreground's backing color.
Output Alpha	Specifies the Alpha channel to use when compositing the image BG & FG Composites the image using both the foreground and background images' alpha channels. BG Only Composites the image using the background image's alpha channel. FG Only Composites the image using the foreground image's alpha channel.

Mask

Controls this operator's Mask Options.

Output

Controls this operator's Output Options.