Aperture Diffraction

Aperture Diffraction lives in Resolve FX Light and models the starburst created when bright light diffracts around the blades of a small lens aperture. Small bright regions create pronounced star patterns while broader bright areas become a more even optical glow with structure and texture.

The most useful mental model is four separate stages: find physically plausible emitters, build a virtual iris, shape the resulting diffraction pass, then composite it back over the image. If Brightness or Result Scale is pushed before source isolation is solved, intensity merely hides upstream mistakes.

Source Regions, Diffraction Alone and Final Result are diagnostic views of one pipeline, not three effects. The first shows the emitter map, the second isolates only the generated pattern and the third shows the final composite.

Resolve 20.2+ gives Input Alpha three explicit modes. Masks The Source Regions constrains the emitter map, Is Used For Compositing preserves alpha for recompositing, and Is The Source Of The Glow makes alpha itself drive emitters. All three refer to embedded alpha in the orange Input image, not a separate Fusion cable.

The blue Effect Mask is a different boundary. It arrives as a separate mask stream and gates spatial contribution of the processed node. Input Alpha and Effect Mask therefore must not be taught as interchangeable masks: one participates inside Light FX source/composite logic and the other gates the node result.

Quality offers Full, Half (Faster) and Quarter (Fast). Blackmagic notes that Full is most valuable for fine point-light details; broad or smooth emitters may show little visible difference at reduced quality.

Source Regions starts with Color Mode. Fast (Greyscale) analyzes brightness quickly; Slow (Color) preserves the colors of different highlight regions. Brightness is the threshold, Gamma shapes matte density, Smooth suppresses fine detail, Color Filter can target a hue, and Morph Operation/Amount refine the already-detected isolation matte.

Source Color Filter and Compositing Color may look similar in the Inspector but belong to different stages. The former decides which colored emitters qualify; the latter tints the finished diffraction when Colorize is raised.

Aperture Controls define optical/design geometry. Iris Shape offers Triangle, Square, Pentagon, Hexagon, Heptagon and Octagon. Aperture Size moves between a pronounced star-like pattern and finer stippled/wave texture, Blade Curvature changes the rays, and H vs V Ratio enables anamorphic-like stretching.

The captured Resolve 21 UI also exposes Preview Shape and Preview Diffraction Pattern. Rotation and Angle are separate controls; in practice they should be judged from the diagnostic pattern, especially when H vs V Ratio makes the geometry anisotropic.

Chroma Shift introduces RGB bleed. It is an optical color-separation stage, not a replacement for colored source analysis or final Colorize, and photographic results usually require moderation.

Diffraction Controls contain Result Gamma and Result Scale. Gamma controls how pronounced light appears between star arms, while Scale moves the calculated result between a more structured pattern and a more diffuse glow. This is still not the final dry/wet stage.

Compositing Controls finish the build: Normalize Brightness helps keep level consistent as highlights change, Brightness sets effect intensity, and Colorize plus Color define tint. Common Settings/Blend remains the final dry/wet control and should not substitute for correct Source Regions tuning.

Aperture Diffraction is Studio-only and generally more processor-intensive than a basic Glow. Moving footage needs temporal QC because noisy Source Regions can flicker and fine star arms can alias after resizing. Captured UI values are reference state, not universal presets.