Merge Node

Merge combines a Background and a Foreground based on the FG alpha. It is the building block of all compositing: every time you layer two images in Fusion, you go through a Merge.

Even the final result of a comp (MediaOut) is usually preceded by a Merge that assembles all the layers. Knowing how to drive a Merge precisely (apply mode, operator, additive slider) is what separates a beginner compositor from a pro.

• Keyboard shortcut: M (in the Node Editor).
• Effects Library: Tools > Composite > Merge
• Quick add: right-click in the Node Editor → Add Tool > Composite > Merge

• Background (orange) - the bottom layer. It sets the output resolution of the Merge.
• Foreground (green) - the layer in front. Positioned and merged over the BG based on its alpha.
• Effect Mask (blue) - optional. Limits the merge to an area. Outside that area, the FG is not visible (BG only).

Critical rule: the output resolution = the BG resolution. If the BG is empty / not connected, the Merge takes the FG resolution but may show unexpected edges.

Basic compositing:
BG shot → Merge BG input
Text+ → Merge FG input
Merge → MediaOut

Multi-layer chain (bottom-up):
BG → Merge1 ← Layer 1
      ↓
    Merge2 ← Layer 2
      ↓
    Merge3 ← Layer 3
      ↓
    MediaOut

Center (X / Y)

Position of the FG in the frame. 0.5 / 0.5 = centered. Works like a built-in Transform.

Size

Scale of the FG. 0 to 5. 1.0 = pixel for pixel. For a quick scale, the Merge Size is simpler than a Transform.

Angle

Rotation of the FG.

Apply Mode

Math blend mode. See the dedicated section.

Operator Mode

Compositing logic (Porter-Duff). See the dedicated section.

Additive / Subtractive

Slider that sets whether the FG is treated as premultiplied or not. Key to solving edge problems.

Alpha Gain

Multiplies the FG alpha linearly. Useful to lower the opacity before compositing.

Burn In

Darkens the BG without touching the additive part of the FG. For additive glow effects that locally burn into the BG.

Blend

Mix between the Merge result and the original BG. 1 = full merge, 0 = BG only. Works like a global opacity fader.

Filter Method

Resampling quality when the FG is scaled/rotated. Catmull-Rom by default (a good compromise). Lanczos / Sinc for high quality, but they can cause ringing.

Edges

Canvas, Wrap, Duplicate, Mirror - how to handle the FG edges beyond its own frame.

The modes used most in production:

Normal (default)

Standard alpha compositing. FG placed over the BG based on the alpha.

Screen

Soft additive light. Ideal for: glow, flares, light, flames, light smoke. Blacks disappear, whites dominate.

Multiply

Whites disappear, blacks dominate. Use it for: shadows, dark textures, dust & dirt.

Overlay

A mix of Multiply (shadows) + Screen (highlights). Boosted contrast. Use it to add a pattern while respecting the original brightness.

Add (Linear Dodge)

Simple math addition. For physical light sources (rays, real flames). Can blow out quickly.

Hue / Saturation / Color / Luminosity

HSL modes that preserve some dimensions of the original color. Color is useful to tint an image while keeping its luminance.

Hypotenuse / Geometric

HDR-optimized. They avoid clipping artifacts when you merge HDR sources (e.g. stock HDR flares).

These modes control the inclusion logic - where does the FG replace the BG?

Over (default)

FG over the BG wherever the FG alpha exists. The standard mode.

In

FG only where the BG alpha exists. The BG acts as a mask for the FG. Useful to confine an image to the shape of another.

Held Out

The opposite of In. FG only where the BG has no alpha.

Atop

FG over the BG, but only where the BG exists. Combines the shape of the BG with the color of the FG.

XOr

Combines BG and FG where only one of them has alpha, never both. A geometric "exclusion" effect.

Conjoint / Disjoint

Variants that handle soft edges and motion blur smartly - fewer artifacts on gradual alphas.

Mask / Stencil

Output = the BG multiplied by the FG alpha (or the inverse). To extract/mask.

Under

The opposite of Over - the BG goes in front of the FG.

The Additive/Subtractive slider sets how the FG alpha is interpreted:

Additive (0)

For premultiplied images (transparent areas are black - the standard case for 3D renders and keyers). The compositing adds the FG to the BG based on the alpha.

Subtractive (1)

For non-premultiplied images (separate alpha, transparent areas have a "full" color even though they are invisible - the case with some scanners).

Edge halo tip: if the FG shows a black / white halo on its edges after compositing, moving the Additive/Subtractive slider often solves the problem. Use an in-between value (0.3-0.7) for ambiguous cases.

Perform Depth Merge

Uses the Z-depth values to decide the layering order pixel by pixel. An FG pixel is only placed in front of the BG if it is closer in Z. Essential to combine 3D renders that intersect (e.g. a character walking into a 3D set).

Foreground Z-Offset

Offsets the depth of the FG. Positive = pushes the FG back, negative = brings it closer.

• Basic composite (text over a shot) - Text+ → Merge FG, shot → Merge BG. Apply Normal, Operator Over.
• Stock lens flare - HDR lens flare → Merge FG, shot → Merge BG, Apply Mode Screen = a flare that adds up like real light.
• Multiplying dust & dirt - a dust scan image → Merge FG, shot → Merge BG, Apply Mode Multiply = dirt blended into the image without crushing the blacks.
• Depth compositing - a 3D character rendered with Z-depth → Merge BG with a 3D set → Perform Depth Merge on = a character that can pass in front of/behind the set elements dynamically.
• Stylized glow - Fast Noise with warm colors → Merge FG, Apply Mode Screen with Blend 0.3 = a subtle glowing halo.
• Multiplied vignette - a radial gradient that is black at the edges → Merge FG, Apply Multiply = a clean added vignette.
• Color pass (localized grading) - a tinted layer → Merge FG, Apply Mode Color = tints the BG luminance without crushing the structure.

• Shortcut M to add a Merge instantly. Memorize it, it is the most used shortcut in Fusion.
• Connect by dragging onto the inputs - in Fusion, dragging a connector from an output to the matching input colors the wire (yellow = BG, green = FG). A lifesaving habit.
• Additive by default is enough - 95% of situations are solved in Additive. The Subtractive slider is only useful on specific sources (old scanned footage).
• Do not scale the FG in the Merge for precise work - for an animated or precise scale, use a Transform upstream. The Merge Size is handy for quick-and-dirty work but less flexible.
• Apply Mode Screen = soft additive - Screen is more "forgiving" than Add (no clipping). Preferred for most lights / glows unless you physically need a true additive.
• Alpha Gain for a fade out - animate Alpha Gain from 1 to 0 = a clean fade out of the FG. Cleaner than animating the overall Blend.
• Avoid stacking 20 Merges - beyond 10 layers, prefer a sub-comp (Group) or pre-render the stacks for readability.
• For transitions between two shots (gradual fade), use the Dissolve rather than the Merge - it offers transition presets (fade, wipe, dissolve).