# Halation and bloom on a Fujifilm X-T5

Public version from AI for Mortals. Educational use only, at your own risk. High-level research notes, not instructions.

## Highlights
1. How it's faked digitally: find the brightest parts of the photo, blur them, tint them red, lay them back on top.
   The open-source app Halationify does exactly this.
2. X-T5 Soft Focus: the camera's own filter already blurs in camera, the best starting point for bloom.
   (It and Clarity -5 soften the whole frame, not just the lights.)
3. Fuji X half: Fuji already built a HALATION filter into this camera, so Fuji's hardware can do it.
4. Fuji X Weekly: has a CineStill 800T recipe for this sensor (Eterna-based, for night) and says halation is
   "glaringly missing" from it.

## What they are and how to make them (research 2026-11-06)

### On film
- Halation: bright light passes through the film, reflects off the base/pressure plate and comes back as a glow
  around overexposed highlights, strongest when the light source is in focus.
  https://help.cinestillfilm.com/hc/en-us/articles/360029185291-What-is-Halation
- It's red-orange because the bounced light re-exposes the bottom (red-sensitive) layer first. Normal film has a
  remjet anti-halation backing to stop it; CineStill removes it.
  https://help.cinestillfilm.com/hc/en-us/articles/360028874012-What-is-Remjet
- Origin claim: Fuji X Weekly says CineStill 800T is Vision3 500T; CineStill says it is "not simply repackaged" motion
  picture film and doesn't name the stock. Don't state the source stock as fact.
- Bloom: light spreading at high-contrast edges around light sources, keeping the light's own colour (starts in the
  lens, film amplifies it). Halation = red-orange halo; bloom = source-coloured glow.
  https://www.dehancer.com/learn/article/bloom https://www.dehancer.com/learn/article/halation

### How it's done digitally (the standard recipe)
1. Mask the brightest pixels (threshold).
2. Blur the mask wide.
3. Tint it red-amber (roughly RGB 1, 0.15, 0).
4. Screen-blend it over the image at a chosen strength. Optional: a second, wider, fainter layer ("aura"), and a
   bloom layer that keeps the source colour.
- Halationify, an open-source app, does exactly this; defaults: threshold 200/255, blur 10, strength 50, blurs
  before and after tinting: https://github.com/FUTC-Coding/halations
- A more physical version works on linear data with an exponential falloff: https://github.com/hotgluebanjo/halation-dctl
- Dehancer and FilmBox expose threshold, radius, hue, strength; FilmBox's "Aura" is the very wide CineStill glow.

### Fujifilm in camera
- X half (X-HF1) has HALATION and SOFT GLOW filters (stills only, can't combine with film simulations):
  https://fujifilm-dsc.com/en/manual/x-hf1/taking_photo/fs_filter/ . Processor undisclosed.
- No other X-series body has halation.
- X-T5: Advanced Filter SOFT FOCUS ("evenly soft throughout") and Clarity -5..+5 (lower = softer; nonzero slows
  saving). Both soften the WHOLE frame; neither is real bloom (bloom is only around light sources) and neither adds red.
  https://fujifilm-dsc.com/en/manual/x-t5/taking_photo/filter/

### CineStill 800T recipes for X-Trans V (Fuji X Weekly)
- v1 (night): Eterna, DR400, Grain Strong/Large, Color Chrome Strong, FX Blue Weak, WB Fluorescent 3 with R-6 B-4,
  Highlight 0, Shadow +2, Color +4, Sharpness -3, High ISO NR -4, Clarity -5, ISO auto to 6400, exp comp -1/3 to +2/3.
- v2 (daylight): Reala Ace, DR200, Grain Strong/Small, CC Off, FX Blue Off, 4500K R-1 B-3, Highlight +2, Shadow 0,
  Color +4, Sharpness -1, High ISO NR -4, Clarity -3.
  https://fujixweekly.com/2024/04/16/cinestill-800t-fujifilm-x-trans-v-film-simulation-recipe/
- The author says halation is "glaringly missing" and suggests a weak diffusion filter (5-10% CineBloom or 1/8-1/4
  Pro Mist) on the lens.

### Options
1. In camera: v1 recipe into a C slot (colours, grain, softness). Real, but no red halation.
2. Firmware: halation inside the camera's processing. Nobody understands the Fuji image pipeline yet, and nobody has done this on an X-T5.
3. On the computer after shooting: Python/OpenCV or ImageMagick using the recipe above. Be clear it's added afterwards.
4. Physical: a diffusion filter on the lens (the recipe author's own suggestion).