Low / High
Defines how much difference is required to become matte.
Set the thresholds so the subject is retained while normal background variation disappears.
← Fusion node reference
Keying & MatteIntermediate
DifferenceKeyer
Key from a clean background reference
Creates a matte by comparing a foreground image to a clean or reference background and isolating the pixels that differ.
DifferenceKeyer
DaVinci Resolve · Fusion
DifferenceKeyer is useful when a stable clean plate exists and color-based chroma keying is not the best way to separate the subject.
Overview
What DifferenceKeyer does
DifferenceKeyer compares the current foreground frame against a background reference. Areas that match the reference are treated as background; significant differences become the subject matte.
This works best with a locked or well-aligned camera, stable lighting and a genuinely representative clean plate. Shadows, exposure changes and camera motion can create false differences.
After the initial separation, matte filters, blur, Contract/Expand and Gamma refine the result. Solid and Garbage mattes are often useful for areas that the comparison cannot resolve cleanly.
Mental model
Think of DifferenceKeyer as asking: “what changed compared with the empty background?” Everything sufficiently different becomes foreground.
Common uses
Remove a static background using a clean plate
Create a motion/change matte
Extract a subject without green screen
Build a technical difference mask
Support set cleanup and compositing
Flow anatomy
Inputs & outputs
The port structure shows how this node fits into a Fusion graph.
Foreground
Image containing the subject.
Background
Clean plate or reference background for comparison.
DifferenceKeyer
Fusion node
Output
Image/matte produced from the foreground-background difference.
Inspector
Important parameters
Start with these controls before reaching for more complicated workarounds.
Filter
Smooths and stabilizes the difference matte.
Fast Gaussian is a practical choice when a soft stable result is needed.
Blur
Softens the matte edge.
Use only enough to reduce chatter; excessive blur disconnects the matte from the subject.
Clipping Mode
Selects the Clipping Mode used by DifferenceKeyer.
Contract / Expand
Shrinks or grows the matte.
Useful for removing edge contamination or recovering a slightly tight key.
Gamma
Controls the density of intermediate matte values.
Helpful for preserving semi-transparent edge detail before clipping.
Solid Matte / Garbage Matte
Combines solid and garbage mattes with the Difference Keyer result.
Post Multiply Image
Multiplies image RGB by the generated alpha.
Useful when preparing the extracted foreground for normal compositing.
Practical setup
A reliable workflow
- 1
Prepare or reconstruct a clean background plate.
- 2
Align the clean plate with the foreground frame.
- 3
Connect foreground and background to DifferenceKeyer.
- 4
Tune Low/High while viewing the matte.
- 5
Refine with Filter, Gamma and small Contract/Expand adjustments.
- 6
Add Solid/Garbage mattes for local problems.
- 7
Finish with MatteControl and Despill/color work if needed.
Typical node chain
Foreground + Clean Plate→
DifferenceKeyer→
MatteControl→
Merge
Examples
Where this node fits in real work
Locked-off actor extraction
An actor is isolated by comparison with the empty set.
ForegroundCleanPlateDifferenceKeyerMatteControlMerge
Change detection
The difference matte becomes a technical mask.
Reference frameCurrent frameDifferenceKeyerBitmap / ColorCorrector
Troubleshooting
Common mistakes
Using the technique with an unaligned moving camera.
Using a clean plate captured under different lighting.
Pushing thresholds so hard that subject detail disappears.
Ignoring shadows that are legitimate differences from the clean plate.
Production notes
Practical tips
Stabilize or align sources before difference keying when necessary.
Inspect the clean plate and difference matte separately.
Local helper mattes are usually better than globally destructive thresholds.
Related nodes