Add red-orange halos to highlights
Place a warm halo around bright edges without washing the whole frame in a neutral glow. The highlight threshold builds a mask, Halo spread blurs that mask outward, and the original highlight is subtracted from the blurred result so most of the color lands around the boundary.
Halation amount controls the final blend. Red-orange bias changes how much green and blue join the added red light.
The film mechanism
Halation appears when strong light passes through the photosensitive layers, scatters or reflects behind them, and exposes nearby emulsion on its return path. Anti-halation backing reduces the effect, but bright sources and high-contrast edges can still produce a colored fringe. The path through color layers gives photographic halation its characteristic red or orange bias.
The digital version uses highlight detection and spatial spread rather than a generic overlay. It responds to the image’s own lamps, reflections, windows, and backlit edges.
Threshold, rolloff, and spread
Highlight threshold decides where the effect begins. A high value restricts the mask to clipped or near-clipped light. A lower value includes pale walls, clouds, skin highlights, and other broad regions that may not read as emitted light.
Highlight rolloff controls how gradually values above the threshold enter the mask. A softer rolloff keeps tonal steps out of skies and gradients. Halo spread sets the radius as a percentage of the shorter side, which keeps the same framing relationship from preview to export.
Halation, bloom, and light leaks
Halation follows bright content and favors a warm fringe. Bloom creates a wider neutral glow from highlights. A light leak is not tied to scene brightness at all; it enters from an edge or patch of the frame as an overlay.
Use halation when the source already contains a believable bright emitter. If a daytime photo has no isolated highlights, forcing a low threshold can tint every light surface instead of creating a photographic edge effect.
Example: neon at night
Start with a threshold near 205, spread at 1.5%, amount near 60%, and a red-orange bias around 70%. Raise the threshold until the halo leaves painted walls and remains around the tubes and reflections. Reduce spread before amount if neighboring letters merge into one red cloud.