A luminance-only Resolve FX keyer. It samples brightness directly in the Viewer, then gives you the same production matte-cleanup stack used by HSL Keyer: range/softness sampling, Invert, two Matte Finesse banks, Garbage Matte and three Output modes.
Mental model
Blackmagic describes Luma Keyer as effectively HSL Keyer with Hue and Saturation disabled. That makes it simple and often sharp: the key is based only on luminance, so colour differences do not matter. The same simplicity is also its limitation when foreground and background share similar brightness.
The first eyedropper creates the initial luminance range. A click samples one luma value, while dragging through the Viewer collects a range. This is the base selection: the other four sampling tools refine it, so the first picker is always the starting point.
The ± range pickers add or remove luminance values from the fully selected core of the key. Add expands the core when required bright or dark levels are missing; Subtract excludes luminance values that were captured by mistake.
The two feather-style pickers control the soft falloff around the selected luma range. Add Softness expands the transition between fully selected and unselected values, while Subtract Softness tightens it. This matters on motion blur, glow, transparency and natural light gradients.
Invert swaps the opaque and transparent sides of the sampled luma range, making bright-key and dark-key workflows equally practical. Reset clears the sampled range without forcing you to remove the whole OFX and rebuild Matte Finesse or Output settings.
Matte Finesse
The supplied Resolve 21 screenshot shows Bank 1. The second bank follows the same morphology model used by HSL Keyer, so the guide documents it as well instead of stopping at the visible controls.
Pre Filter smooths problematic image structure before final matte cleanup. On compressed or noisy footage, neighbouring pixels can fluctuate in luma and produce a chattering key edge. A small amount can stabilise the selection, while excessive filtering removes fine detail.
Clean Black removes grey contamination from the black/background side of the matte and pushes it toward pure black. Clean White does the opposite in the foreground, filling grey or dark holes and driving selected regions toward solid white. This is the softer cleanup stage before hard clipping.
Black Clip and White Clip normalise grey matte values more aggressively than Clean Black/White. In the supplied panel Black Clip is 0 and White Clip is 100, the neutral endpoints. Raising Black Clip rejects more dark-grey contamination; lowering White Clip turns light-grey regions into solid white sooner.
Blur Radius softens the already-built matte and suppresses small edge chatter. In/Out Ratio biases that processing relative to the boundary: around zero it is symmetric, negative values pull the treatment inward and positive values push it outward. This is useful for halo control and for restoring edge position after a small blur.
Button 2 opens the second Matte Finesse bank with morphology controls: Operation offers Shrink, Grow, Opening and Closing; Shape offers Circle, Square and Diamond; Radius sets the kernel size; Iterations repeats the operation. This is the same class of matte repair exposed separately in Alpha Matte Shrink and Grow.
Garbage Matte + Output
Matte Shape offers None, Rectangle and Ellipse. Rectangle or Ellipse is a coarse spatial limiter: it keeps irrelevant areas of the set out of the keying problem before you start over-cleaning the luminance matte itself.
As in HSL Keyer, enabling a shape exposes its placement/size controls and edge softness/inversion controls. Use Open FX Overlay to position the matte directly in the Viewer where practical.
Output offers Alpha Highlight, Alpha Highlight B/W and Final Composite. Alpha Highlight is a diagnostic overlay that keeps solid regions recognisable; Alpha Highlight B/W exposes the matte itself and is the best mode for sampling and Matte Finesse; Final Composite shows the keyed image over the track below.
Production workflow
Enable Open FX Overlay and use the first eyedropper to sample the required luminance range in the Viewer.
Use Add/Subtract Luma Range for the core selection and Add/Subtract Softness only for its outer falloff.
Switch to Alpha Highlight B/W: correct sampling first, then Clean Black/White, and only then use Clip.
Use Blur Radius and In/Out Ratio for fine edge stabilisation without turning the matte into a soft blob.
If irrelevant set areas exist, constrain the problem with Garbage Matte and add Bank 2 morphology only when needed.
Return to Final Composite and judge the edge against the real background: B/W matte is diagnostic, the composite is the final criterion.
FAQ
Luma Keyer uses brightness only. Conceptually it is HSL Keyer with Hue and Saturation disabled, so it cannot distinguish two regions that have the same luma even if their colours are completely different.
When separation is fundamentally based on brightness: white/black backgrounds, skies and highlights, luminous elements, high-key/low-key graphics, smoke, some heavily compressed sources and creative composite-mode workflows.
The sampled range is usually too wide or Matte Finesse is too aggressive. Tighten range/softness first, move Clean/Clip closer to neutral, and only then inspect Blur or morphology.
Alpha Highlight B/W is best for technical matte inspection. Alpha Highlight keeps solid regions in colour while visualising transparency. Final Composite is for the final edge check over the underlying video.
Next steps
Previous FX
Return to the colour-aware H/S/L variant and compare the same luma logic with Hue and Saturation available.
Use multidimensional colour sampling when brightness alone cannot separate the subject from the background.
Compare Resolve FX keyers with the node-level HSL/3D qualifier workflow on the Color page.
Next FX
Open the new Resolve FX Light category with source-region isolation, virtual aperture geometry and diffraction controls.
Resolve FX catalog
The Key category contains 3D Keyer, Alpha Matte Shrink and Grow, HSL Keyer and Luma Keyer.
