COLOR / TWO-INPUT SIGNAL COMBINER
Custom
Mixer.
Mix two grades.
Know which key matters.
Not merely opacity: Custom Mixer combines two RGB sources, obeys the second-input alpha mask, passes the first-input key onward, and offers Blend/Combine with per-channel values and explicit working context.
2 × RGB + Key
Blend / Combine
Composite / Gamma
Try Blend → Combine, then switch the Input 2 alpha mask. The image changes because the formula changes—not because a label is animated.
Independent educational image model. The Color Space/Gamma selectors above illustrate the importance of processing context: they are not accurate ACES, Adobe RGB or Resolve OFX conversions. Extreme math is clipped only for display. Use the genuine Inspector captures below when setting Resolve.
Original captures + independently testable teaching model
17 documented entries · 8 PNG01 / THREE SIGNALS TO UNDERSTAND
Blend, Combine and alpha are different questions.
A two-input mixer is not an RGB channel swapper. First understand source contributions and masks; only then adjust composite math.
Blend: one crossfade weight
0 leaves the base input unchanged. 1 selects the second input where its alpha is 1. Values outside the interval extrapolate the difference.
Combine: two sources and Offset
Adjust Input 1, Input 2 and Offset independently. In Split Channels you can inspect component-specific contributions.
Second alpha gates the RGB mix
Input 2 key defines WHERE to mix. Input 1 key is passed to output. The two are not interchangeable.
The lab uses display-clamped educational math and simplified gamut/gamma proxies, not a precise emulation of DaVinci Resolve’s proprietary OFX or OCIO transforms.
02 / NATIVE INSPECTOR + FULL CONTROL REFERENCE
Explain what is actually on screen — and what is in the manual.
The gallery uses all eight original PNGs. Historic filenames are mismatched; captions describe actual visible controls. Combine details are sourced to the Resolve 21 manual.
01 / INPUT
Two-source routing and signal logic
First verify both incoming images. No amount of slider tuning repairs swapped connections.
- Input 1 · RGB
The upper green Color-node input is the base image. Its key passes to the output; input 1 alpha does not control the strength of input 2.
- Input 2 · RGB
The lower green input receives an alternate version of the shot or another aligned source. Match frame, dimensions and timing for meaningful blending.
- Input 2 · Alpha/Key
The alpha of input 2 gates the mixing area. A zero mask leaves input 1 visible even if Blend has a high value.
- Input 1 · Output Key
Input 1 alpha is not the Blend mask; it passes through as the output key. Do not confuse final transparency with the alpha gating RGB input 2.
- Resolve FX node placement
Add Custom Mixer as a dedicated FX node in the Color Node Graph (Resolve FX Refine). Do not drop it onto an existing Corrector when you need two separate green inputs.
02 / BLEND
Mix Mode, Blend and Split Channels
The captured Inspector says Split Channels; the reference manual calls the equivalent ganging behavior Gang. Our UI labels follow the actual screenshots.
- Mix Mode · Blend / Combine
Both modes mix the same two inputs using different exposed controls. Blend sets the contribution of input 2; Combine exposes independent source contributions and an Offset.
- Blend Input 2 onto 1
At 0 the mix returns Input 1; at 1 it uses Input 2 inside its alpha. The reference allows typed values beyond 0–1 (up to tenfold in either direction) to exaggerate differences between sources.
- Split Channels / Gang
With Split Channels off, one RGB value moves all channels together. Enabling it exposes channel-specific controls (equivalent to unganging channels in the manual).
- Keyframing
Individual channel amounts can be independently keyframed. Watch for colored flashes between keys if R/G/B values drift apart.
03 / COMBINE
Combine: three contribution groups
The archive does not contain an open Combine panel. These labels and behaviors come from the Resolve 21 manual, not from a fabricated Inspector screenshot.
- Input 1 Contribution
Sets the independent contribution of source 1. Unlike Blend, this can amplify or reduce the original branch separately from input 2.
- Input 2 Contribution
A separate coefficient for input 2. At zero, source 2 contributes no RGB to the Combine result.
- Offset
Offsets the computed combination. Watch scopes: a large Offset can push values beyond the expected display range.
- Separate channel contributions
Each contribution group can be unganged per component in the selected Color Space. In YUV or XYZ the individual components are not ordinary RGB sliders.
04 / ADVANCED
Advanced Options and color safety
Composite Type, Color Space and Gamma define the working context, not cosmetic switches. Visible menu choices are grounded in native captures.
- Composite Type
Normal is the baseline. The captured list also shows Add, Subtract, Difference, Multiply, Screen, Overlay, Hard Light, Softlight and Darken. Test clipping and signed differences on a controlled frame.
- Color Space
Use timeline inherits the timeline primaries. The dropdown also includes ACES (AP0/AP1), Adobe RGB, ARRI Wide Gamut 3/4 and Blackmagic entries. This changes the math context, not just the look of the finished composite.
- Gamma
Use timeline inherits the project context. The capture includes ACEScc, ACEScct, Apple Log, ARRI LogC3/4 and Blackmagic Film. Double-transforms around a managed pipeline can invalidate the intended composite.
- Scopes and render QC
Compare source and result on waveform, parade and a short rendered export. Pay special attention to Combine Offset, Blend values beyond 0–1 and HDR transitions.
03 / WIRE THE SIGNALS
Two green RGB inputs. Two different alpha responsibilities.
Most confusing Custom Mixer behavior starts upstream, not inside Advanced Options. Select each signal in the graph.
The blue key of input 2 gates how much of input 2 reaches input 1. It is not the output image transparency.
Green paths carry RGB, blue paths carry Key/Alpha. This interactive wiring sketch is a teaching diagram, not a screenshot of the Resolve Color node graph.
Learn more: Color Node Graph ↗ · Keys / Power Windows ↗
04 / A CALIBRATION TABLE
Choose a mixer, not a mystery.
These are practical starting states, not universal presets or guarantees of pixel equality inside Resolve.
| Goal | Blend | Combine | Watch |
|---|---|---|---|
| Keep Input 1 | Amount = 0 | Input 1 = 1; Input 2 = 0; Offset = 0 | Incoming key and alignment |
| Use Input 2 in the mask | Amount = 1 | Input 1 = 0; Input 2 = 1; Offset = 0 | Input 2 alpha gates the result |
| Exaggerate a difference | Amount > 1 or < 0 | Independent contributions / Offset | Highlight clipping and negative values |
| Split RGB components | Split Channels = ON | Split Channels = ON | Color bias and gamut |
Color Space and Gamma selections can change the mathematical meaning of those weights. In managed projects, return to Use timeline when diagnosing an unexpectedly bright or colored result.
05 / FOUR CONTROLLED EXPERIMENTS
Test a principle on real footage before saving a preset.
The procedures below use actual Color nodes and the genuine Resolve Inspector. Numerical ranges in the lab are educational.
Amplify or reduce noise
Compare original and a parallel Noise Reduction branch.
- 01
Split the original RGB into two branches; add Noise Reduction to the second.
- 02
Connect branches to both green inputs of Custom Mixer.
- 03
In Blend, compare 0→1, then test 1.5 and a negative value as an experiment.
- 04
Compare faces and shadow detail using scopes, motion and a short render.
Values above 1 can amplify a difference rather than simply add opacity.
Mix under an alpha mask
Separate RGB sources from the region in which they are mixed.
- 01
Feed the base grade as input 1 and an alternative as input 2.
- 02
Limit the alpha of input 2 using a Window/Key, leaving the output key from input 1 intact.
- 03
In the lab, switch the second alpha Full → Radial → Left with the same Blend value.
- 04
Inspect feathered edges and subject motion.
Where second alpha is zero, input 1 remains regardless of Blend amount.
Test independent contributions
Explore Combine without compensating slider changes.
- 01
Choose Combine; begin at Input 1 = 1, Input 2 = 0, Offset = 0.
- 02
Increase only Input 2 Contribution while keeping input 1 fixed.
- 03
Test Offset and Split Channels separately.
- 04
Return to neutral and document which parameter caused each change.
Input 1, Input 2 and Offset are not a single opacity control.
Check Color Space/Gamma context
Avoid mistaking a change in processing math for an automatic image improvement.
- 01
Start with Use timeline for both Color Space and Gamma.
- 02
Change Composite Type while keeping both sources fixed; inspect the output.
- 03
Only then test a consciously selected Color Space/Gamma pair.
- 04
Compare scopes and rendered output in the managed project.
Any Color Space/Gamma change requires verification rather than copying settings blindly.
06 / THE RIGHT TOOL
Custom Mixer is not the same as RGB Mixer or CST.
| Tool | Best use |
|---|---|
| Layer Mixer | For visually compositing branches without fine per-channel extrapolation. |
| RGB Mixer | For remapping channels within one image, not compositing two RGB inputs. |
| Custom Mixer | For mixing two inputs with Combine/Offset, second-input alpha and explicit processing context. |
| Color Space Transform ↗ | For explicit color/gamma conversion, not weighing two incoming image sources. |
07 / DIAGNOSE THE SIGNAL
A black key is not a faulty Blend formula.
Check routing, alpha, channel separation and processing context in that order.
01Input 2 is invisible+
Cause: Blend is zero, input 2 alpha is black or the second RGB input is disconnected.
Fix: Check the lower green RGB port, then second-input alpha, then Blend.
02Unexpected output transparency+
Cause: The output key follows input 1, not the second input mask.
Fix: Inspect input 1 key and Alpha Output routing instead of trying to fix RGB Blend.
03Highlights clip or look too hot+
Cause: Large Blend/Combine Contribution/Offset or Add in the chosen gamma context.
Fix: Return to Normal, coefficients around 0–1 and Use timeline; inspect scopes.
04Unexpected red/blue tint+
Cause: Split Channels is enabled and per-channel coefficients differ.
Fix: Disable Split Channels or align R/G/B, then check the color-space context.
05Transition breaks during motion+
Cause: Branches have different timing or the second-input key fails to track the object.
Fix: Check frame alignment and key tracking; Composite Type is not the remedy.
06Blend and Combine look identical+
Cause: Equivalent neutral contributions can yield the same signal in both modes.
Fix: Test Combine Offset and an independent input 1 coefficient.
07Screenshot appears to show a different menu+
Cause: Historical filenames of the eight source PNGs do not always match the captured control.
Fix: Use the visible-pixel labels in the gallery. The source files are unchanged.
08 / BEFORE DELIVERY
Check the moving result and the output key.
09 / FAQ
Practical Custom Mixer questions
Is Custom Mixer the Color page RGB Mixer?
No. Custom Mixer is a separate two-input Resolve FX node with Blend/Combine and Advanced Options.
Why is the second RGB visible only inside a mask?
The manual says input 2 alpha gates its contribution to input 1. It is not the general Output Alpha.
What does Split Channels actually do?
The screenshot labels per-channel ungrouping Split Channels; the manual describes the same idea as disabling Gang.
Should Combine use 0.5 on both contributions?
There is no universal ratio. Begin at Input 1 = 1, Input 2 = 0, Offset = 0 and tune the other contribution deliberately.
Can Blend exceed 1?
Yes. The manual documents extended typed blend values for extrapolating differences. Watch for clipping.
Does the Color Space selector replace a CST?
No. It sets the mixer’s working context, not a universal input/output color-management transform.
Why is there no native Combine panel screenshot?
The eight source PNGs do not show an expanded Combine pane, so the controls are documented from the manual without a fabricated capture.
Sources, screenshots and limitations
The eight PNGs are native screenshots from the provided site archive. Some historic filenames are swapped; the guide labels what is actually visible. The official manual describes channel ganging as Gang, while the captured Resolve interface reads Split Channels. Combine fields, alpha/key routing, and extrapolated blend values are documented in the Resolve 21 reference. The lab is a deliberately approximate educational model, not an implementation of Blackmagic’s renderer, RGB/YUV/XYZ transforms, ACES, LogC or gamma algorithms.