Alpha Over Node

The Alpha Over node composites two images by layering the Foreground image over the Background, using standard alpha blending operations.

This node is commonly used to combine rendered elements, overlays, or visual effects in a single image, such as placing text, logos, or transparent effects over footage.

Inputs

Background

The background image.

Foreground

The foreground image to be placed over the background.

Factor

Controls the opacity of the foreground image, from 0 (fully transparent) to 1 (fully opaque).

Type

Determines the alpha compositing method:

Over:

The standard alpha-over operation. The foreground is placed over the background based on its alpha channel.

Disjoint Over:

Similar to Over, but assumes the background has been held out by the foreground, resulting in cleaner edges when compositing multiple layers.

Conjoint Over:

Similar to Over, but assumes the foreground overlaps or extends into the background. Useful when the foreground is more opaque but not fully opaque.

Straight Alpha

Specifies whether the foreground uses straight alpha (unpremultiplied) instead of premultiplied alpha. Most images in the compositor are premultiplied, so this should remain disabled in most cases. Enable it only if the foreground has been explicitly converted to straight alpha form.

Outputs

Image

The combined image after alpha compositing.

Examples

Disjoint / Conjoint / Over

The example below shows how different alpha compositing types affect the blending of multiple layers. Four image layers are assembled using the Disjoint, Conjoint, and Over methods to create depth between overlapping elements.

Assembling a composite image using Alpha Over.

Fade In

This example uses a Time Curve Node to gradually animate the Factor input of the Alpha Over node from 0 to 1 over 30 frames. The result is a smooth fade-in of text over a background image.

Animated fade-in effect using Alpha Over.