What does Aperture Diffraction do?

It models diffraction on the blades of a virtual aperture and turns selected bright regions into starburst and optical glow patterns.

Which Iris Shapes are available?

Triangle, Square, Pentagon, Hexagon, Heptagon and Octagon. The polygon changes the geometry and directional structure of the diffraction pattern.

What does Input Alpha do?

In Resolve 20.2+, alpha can mask Source Regions, be used only for compositing, or become the source of the glow/diffraction itself.

Why use Diffraction Alone?

It displays only the generated diffraction pattern, making aperture geometry and Result Gamma/Scale much easier to judge.

Resolve FX Light · Studio

Aperture Diffraction

A physically inspired light effect that turns selected highlights into diffraction patterns shaped by a virtual iris. Resolve 21 exposes source selection, alpha routing, quality, aperture geometry, diffraction shaping, compositing and Global Blend in one compact but deep pipeline.

3 Input Alpha modesFull / Half / Quarter6 Iris ShapesDiffraction + Composite

Mental model

Source → virtual aperture → diffraction → composite

The fastest way to understand the plugin is to separate four jobs: first identify which pixels emit light, then define the virtual iris, then shape the resulting diffraction pattern, and only after that decide how strongly it is composited over the shot. Mixing these stages is the main reason the effect quickly becomes artificial.

Three live viewing stages

Source Regions / Diffraction Alone / Final Result

In the current Resolve 21 panel, the three top tabs separate source isolation, the generated diffraction pattern and the final composite. Source Regions is for deciding which bright areas drive the effect, Diffraction Alone shows only the generated optical pattern, and Final Result places it back over the original image.

Source Regions diagnoses the emitters: headlights, sun, lamps and specular highlights.
Diffraction Alone is the best view for Aperture Size, Blade Curvature, Rotation, H/V Ratio and Chroma Shift.
Final Result is where you judge whether the effect still looks plausible in the shot.

How alpha participates in the Light FX

Input Alpha

Resolve 20.2+ added explicit input-alpha handling to Light FX. Aperture Diffraction exposes Masks The Source Regions, Is Used For Compositing and Is The Source Of The Glow, so alpha can constrain detected highlights, participate only in compositing, or fully drive the glow-source map.

Masks The Source Regions constrains the areas from which diffraction may be generated.
Is Used For Compositing keeps alpha in its normal compositing role.
Is The Source Of The Glow makes alpha itself the emitter map, especially useful after Fusion or matte-driven workflows.

Speed versus quality

Quality

Aperture Diffraction is more computationally expensive than a basic Glow, so Quality matters during setup. Full is the final-quality mode, Half (Faster) is a practical working preview, and Quarter (Fast) is useful for quickly finding the shape and composition on heavy timelines.

Do not judge fine diffraction texture in Quarter; re-check the final result in Full.
Build motion and overall timing in Half or Quarter, then return to Full before delivery.

Aperture Controls

The iris determines the geometry before intensity is added

These controls define the optical character of the generated pattern. Treat them as lens geometry rather than simple glow sliders.

Virtual aperture geometry

Iris Shape

Iris Shape defines the polygon of the virtual aperture and therefore the character of the diffraction rays. The menu contains Triangle, Square, Pentagon, Hexagon, Heptagon and Octagon. Hexagon is selected in the supplied panel.

Triangle and Square produce more graphic, immediately recognisable starburst forms.
Pentagon and Hexagon often feel closer to photographic apertures with visible blade structure.
Heptagon and Octagon create denser, more circular patterns with more directional arms.

Built-in shape diagnostics

Preview Shape / Preview Diffraction Pattern

Preview Shape lets you inspect the virtual aperture itself instead of inferring it from the glow. Preview Diffraction Pattern shows the optical pattern generated by the current aperture settings, which is especially useful while tuning Blade Curvature, Rotation and Chroma Shift before balancing brightness.

Solve shape and geometry first, Result Gamma/Scale second, and Compositing Brightness last.
This keeps optical shape separate from simple glow intensity.

Pattern size and character

Aperture Size

Aperture Size changes the structure of the diffraction result: higher values produce a more pronounced star-like pattern, while lower values move toward a finer stippled or wave texture. The supplied panel shows 8.00, a strong starting point for a clearly visible pattern.

Do not confuse Aperture Size with Result Scale: the first changes the aperture behaviour, the second scales the resulting diffraction response.

Ray shape and optical character

Blade Curvature / Rotation / H vs V Ratio / Angle / Chroma Shift

Blade Curvature changes the softness and character of the arms; Rotation turns the pattern; H vs V Ratio stretches the aperture horizontally or vertically for anamorphic-like behaviour; Angle sets orientation; Chroma Shift separates RGB components to introduce coloured optical bleed.

H vs V Ratio is useful for broad horizontal streaks and pseudo-anamorphic looks.
Use Chroma Shift moderately; large values quickly turn an optical effect into overt stylisation.
Rotation and Angle can be animated, but realistic optics usually benefit from motion that follows camera or light behaviour.

Source + diffraction + composite

Every remaining control belongs to a different stage

Which highlights generate diffraction

Source Regions

This group is collapsed in the supplied screenshot, but it is the stage that decides which parts of the frame become emitters. Aperture Diffraction uses colour or greyscale source analysis, a Brightness threshold, Gamma shaping, Smooth for suppressing fine detail, a Color Filter with eyedropper, and a morphological Operation for refining the isolation matte.

Brightness sets the threshold above which highlights enter Source Regions.
Gamma reshapes the density of the isolated bright regions.
Smooth suppresses fine texture so it does not replicate through the diffraction pattern.
Color Filter restricts the emitters to a chosen colour, sampled directly from the Viewer with the eyedropper.
Operation provides Shrink, Grow, Opening and Closing for morphological cleanup of the source matte.

Final shape of the optical pattern

Diffraction Controls

Result Gamma controls how strongly glow appears between the starburst arms, while Result Scale shifts the result between a pronounced structured pattern and a more diffuse glow. This stage no longer chooses emitters or iris geometry; it shapes the calculated diffraction result itself.

Result Gamma controls the density and prominence of light between the rays.
Higher Result Scale values emphasise the star pattern; lower values make it more diffuse.

Brightness, colour and stability

Compositing Controls

Normalize brightness scales the diffraction brightness into a more natural range and helps keep the overall effect level more consistent as the scene changes. Brightness sets intensity. Colorize determines tint amount, while Color defines the tint used once Colorize is raised above zero.

Normalize brightness is especially useful on moving footage with changing highlights.
Adjust Brightness after Source Regions and aperture geometry are already stable.
Colorize plus Color lets you keep the physical diffraction shape while art-directing its hue.

Final dry/wet control

Global Blend

Blend is the final master intensity control for the whole Resolve FX. If the diffraction shape is already correct but feels too strong, reduce Global Blend instead of rebuilding Source Regions or Aperture Controls.

1.000 is the full effect; lower values bring back more of the original image.
It is a good final step after Brightness and Colorize are set.

Practical workflow

A reliable order for real shots

1. Isolate sources

Use Source Regions and, when appropriate, Input Alpha. The goal is to make only physically plausible emitters drive the effect.

2. Build the iris

Choose Iris Shape, then tune Aperture Size, Blade Curvature, Rotation, H/V Ratio and Angle while looking at Diffraction Alone.

3. Shape diffraction

Use Chroma Shift, Result Gamma and Result Scale to move from neutral optical behaviour to a stronger stylised look.

4. Composite last

Return to Final Result, set Normalize brightness, Brightness and Colorize, then use Global Blend for the final restraint.

FAQ

Practical Aperture Diffraction questions

How is Aperture Diffraction different from a normal Glow?

Glow primarily creates soft light spread. Aperture Diffraction models diffraction on the blades of a virtual aperture, so it can create starbursts, polygon-driven structure and a more optical pattern. It is usually more computationally expensive.

What should I tune first: Brightness or Iris Shape?

Start with Source Regions, then Iris Shape and the other Aperture Controls, then Result Gamma/Scale, and finish with Compositing Brightness, Colorize and Global Blend. This prevents intensity from hiding shape problems.

When should I use Is The Source Of The Glow?

Use it when a prepared alpha or matte already comes from Fusion or another VFX chain and you want that alpha to define the diffraction emitters instead of automatic highlight detection.

How do I get an anamorphic-like diffraction pattern?

Start with H vs V Ratio, then tune Angle or Rotation, and only after that adjust Result Scale. A moderate Chroma Shift can add a stronger optical colour separation.

Next steps