Merge

Composites a foreground image over a background using Porter-Duff alpha compositing with blend modes.

Category: Composite Menu path: Composite > Merge

Ports

Port	Type	Direction	Description
inputs	imageRgba16f	input (multi)	Any number of images, composited as a stack — the first-evaluated input is the bottom, the last is on top.
out	imageRgba16f	output	Composited result

Legacy two-input projects (fg/bg ports) still load and behave as a two-image stack [bg, fg].

Parameters

Param	Type	Default	Description
blendMode	enum	Normal	Blend mode for compositing. Options: Normal, Add, Multiply, Screen, Overlay. Keyframeable.
opacity	scalar	1.0	Foreground opacity (0 = fully transparent, 1 = fully opaque). Keyframeable.

How It Works

The shader applies the selected blend function pairwise up the stack, compositing each input over the accumulated result using the Porter-Duff "over" operator with premultiplied alpha.

Input order

The Inputs list in Properties reads like a layer stack: the top row renders on top. The wire fan on the node's input pill matches — the top slot is the top of the composite. Reorder by dragging a row's handle, with the up/down arrows, or leave the graph wiring untouched and only change the order. Newly connected inputs land on top of the stack.

Blend Modes

• Normal -- foreground replaces background where it has alpha
• Add -- foreground + background (brightens, good for light effects)
• Multiply -- foreground x background (darkens, good for shadows and texture overlay)
• Screen -- inverse of multiply: fg + bg - fg x bg (lightens, good for glows)
• Overlay -- multiply where background is dark, screen where background is bright (contrast enhancement)

The opacity parameter scales the foreground's alpha before blending, so reducing opacity fades the foreground contribution.

Usage Examples

Basic: Layer two images

1. Connect both images to inputs — the Properties list shows which is on top; drag to swap
2. Leave blend mode on Normal and adjust opacity
3. This is the same operation the timeline does when compositing layers, but within a single layer's node graph

Creative: Light effects with Add

1. Connect a glow or particle render to fg
2. Connect the scene to bg
3. Set blend mode to Add for additive light blending where bright areas stack

Advanced: Texture overlay

1. Connect a texture or grunge image to fg
2. Connect your main image to bg
3. Set blend mode to Multiply and reduce opacity to 0.3-0.5 for a subtle darkening texture overlay
4. Try Overlay instead for texture that affects both highlights and shadows

Tips

• Merge is the same compositing operation the engine uses for layer compositing in the timeline. Use it within a node graph when you need to combine textures at an intermediate stage.
• The Output node provides blend mode and opacity for final layer compositing. You only need Merge for in-graph compositing.
• Add mode can push values above 1.0 in the linear working space, which is useful for HDR-style effects.
• With a single connected input, the result is that input with opacity applied.

Related Nodes

• Mix -- crossfade between two images with an optional mask
• Matte -- cut out regions using alpha/luminance masks
• Blur -- soften before merging for glow effects