COLOR / TOOL GUIDE 09 / 13
Key.
Separate the matte from correction strength.
Key Input, the internal key and Key Output serve different purposes. Learn to reduce a secondary correction without breaking technical transforms or adjacent branches.
external matte through the blue key connection
the node's internal matte
the matte the node sends downstream
Verified captures from the site library. Choose a panel and open a larger view. Layout and available controls may vary with your Resolve version and configuration.
BEFORE MOVING A CONTROL
Understand what you are changing.
RGB and key travel along different paths
The image and matte are different signals. An external key arrives at the blue input, while the node can form its own internal selection. Before changing Input Gain, determine whether an external key is connected and what it contains.
Key Output Gain is commonly used to reduce an approved correction on one node. Its result still depends on graph structure, the node’s operation and how downstream branches use its key signal.
Gain and Offset affect a matte differently
Gain changes key strength; Offset shifts its values. On soft edges this can alter both the apparent correction strength and the transition participating in it. Inspect the edge in matte and normal image views.
Blur does not fix incorrect selection or tracking. If background leaks into the matte, blur spreads the influence further. Repair the key source first, then shape softness and strength.
Do not apply a technical transform halfway
Reducing a creative look and reducing a required color-space transform are different actions. If a LUT or CST changes technical encoding, blending it via Output Gain may create an intermediate state not expected by the next operation. Keep technical and creative nodes separate.
The final node is not automatically a master strength control for every upstream correction. Reducing its contribution does not reduce the whole preceding chain. Define the operations and grouping of a composite look before controlling its overall strength.
FROM PURPOSE TO CONTROL
Choose deliberately, not by trial and error.
The interface images are collected in the viewer above. Here, focus on what each control changes and when to use it; values in the captures are not universal presets.
Input key, output and Qualifier
Key Input Gain
Controls the strength of the incoming key signal. It is useful when a matte or alpha connection already feeds the node and its influence needs to be changed before the correction is applied.
Key Input Offset
Shifts the incoming key level. In practice it can open or close more of the affected range, but strong values can quickly make the matte overly hard.
Blur R. / Blur H/V
Softens the incoming matte. Radius controls the overall blur amount, while H/V changes the horizontal-versus-vertical character of that blur. It is useful when the key edge is too sharp or visibly noisy.
Key Output Gain
The most common practical use is to treat Output Gain as the intensity of the whole node. If a look or local correction is too strong, you can reduce it with one control instead of rebuilding the node.
Key Output Offset
Changes the level of the output key signal. It is more specialized than Output Gain and is usually most useful when you already understand how the key travels through the node tree.
Qualifier Gain / Offset
A separate adjustment for the key generated by the Qualifier. This does not replace the Qualifier page: there you build the isolation, while here you modify the strength and level of the finished qualifier key.
TECHNICAL REFERENCE
The Key Palette controls how a matte enters, is shaped and leaves a node — not which colour is selected
In a Corrector node, the Key Palette has three logical parts. Key Input modifies an external key arriving through the blue key connection. Qualifier controls refine the internal matte created by a Qualifier/Window. Key Output controls the matte sent downstream, while Output Gain also acts as a convenient overall control for the node's contribution to the final grade. This is why Output Gain is often used to reduce a LUT/look/secondary correction once the correction's internal balance is right and only its overall weight needs changing.
The key-signal path through a Corrector node
| Stage | Source | Controls | Practical meaning |
|---|---|---|---|
| Key Input | blue key connection from another node/matte | Gain, Offset, Blur, H/V Ratio, Invert | accept, soften, reduce or invert an external matte |
| Internal Qualifier | Qualifier, Power Window and internal key logic | Gain / Offset plus matte finesse in the relevant palettes | define where the correction in this node has influence |
| Key Output | the node's resulting matte | Gain, Offset, Invert | control the matte sent through the key output connection |
| Output Gain as node mix | the node's entire correction | Key Output Gain | reduce a look/LUT/secondary correction without rebuilding internal controls |
| Outside node | key from the previous node | automatically inverted Key Input, controllable in the Key Palette | work on everything outside the original selection |
| Layer Mixer | RGB layers + key opacity | Output Gain on the layer node | behave like opacity for a keyed layer |
FROM KNOWLEDGE TO A REPEATABLE RESULT
One exercise. A result you can check.
Use a dedicated creative or secondary Corrector node and retain its starting version. Do not start with the sole log-to-output transform node: partially mixing that transform produces an incorrect technical foundation.
- 01
Start with the local task
A Qualifier, Window, Magic Mask or alpha connection defines where the correction works. The Key palette makes sense once that isolation already exists.
- 02
Check the matte in black and white
White means full influence, black means no influence and gray values produce partial influence. Make the matte readable first, then judge the picture.
- 03
Reduce the node with Key Output Gain
If the correction itself is good but too strong, there is no need to rebuild Wheels or Curves. Output Gain can make the result feel more natural very quickly.
- 04
Do not rescue a bad key with Gain and Blur alone
The Key palette is excellent for refining a reasonable signal, but it does not replace a proper Qualifier, Window or Magic Mask. If the isolation is fundamentally wrong, fix the source of the problem.
Self-check in Resolve; the site does not evaluate your work. Progress is not saved after reloading.
An editorial exercise for your own footage, not an automated check of a Resolve project. Work on a copy or separate version and evaluate the complete shot.
WHEN THE RESULT IS NOT WHAT YOU EXPECT
Find the cause, not a compensating slider.
01Output Gain 0.5 changes the grade differently than expected+
Possible cause. the node participates in a Layer/Parallel Mixer or its key/connection topology changes the compositing behaviour
What to check. node graph, mixer type, key connections and bypassing the whole branch
02An Outside node affects the inside of the original mask+
Possible cause. Key Input invert was changed or routing is not a standard Outside configuration
What to check. Key Input Invert and the blue key connection from the source node
03Matte blur stretches only horizontally/vertically+
Possible cause. Blur H/V Ratio is offset from its neutral value
What to check. Key Input Blur Radius and Blur H/V Ratio
04Reducing Output Gain does not change an external key as expected+
Possible cause. node contribution is being confused with the key signal sent to another branch
What to check. separate the tasks: Key Output for matte routing and node correction mix for visual contribution
A SITUATION TO THINK THROUGHReducing Output Gain on a log-to-Rec.709 LUT node made the image greyer. Is this the right way to soften the look?Compare your reasoning ↓
You are weakening technical normalization together with the look. Separate signal conversion from creative adjustment, then vary only the creative contribution. LUT strength cannot be judged without understanding its expected input and output.
Sources and version notes
Checked against Blackmagic Design’s Color documentation and the relevant new-feature guides. Screenshots are from the site’s own supplied library; controls and layout can differ between versions. Examples are instructional, not universal production settings.
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