What halation is, and how to fake it properly

26 September 2026

Halation is the reddish glow that forms around bright lights on film. Light passes through the emulsion, bounces off the back of the film base, and exposes the emulsion a second time from behind, a little to the side of where it first landed. Digital sensors don't do it, so on a phone it has to be added, and most of the ways it gets added look wrong.

This post explains where halation comes from, why it's red, why anti-halation layers exist, and what a convincing fake needs to get right. At the end there's how we model it in Chobial, and how much is too much.

What is halation in photography?

Film is a stack of thin, light-sensitive layers coated on a transparent plastic base. Most light that hits it is absorbed by the emulsion. Some isn't. On a bright source such as a street lamp, a neon sign or the sun glinting off chrome, enough light gets all the way through the emulsion and into the base.

At the back of the base, some of that light is reflected: at the boundary between the base and the air behind it, and, some sources say, off the camera's pressure plate. It travels back up through the base at an angle and re-enters the emulsion from behind, a short distance from where it came in. That second exposure is the halo. The name comes from "halo".

Because the light spreads out as it goes down and back, the glow forms a soft ring around the source rather than on it. The source itself is usually already overexposed to pure white, so the halo is what you notice: a warm fringe on the dark side of the edge. Analog.cafe's explainer covers the reflection geometry in more detail, and argues that the base-to-air reflection matters more than the pressure plate.

Why is halation red?

Two reasons, and they add up.

The first is the order of the layers. In a colour negative, light meets the blue-sensitive layer first, then a yellow filter that stops blue from going further, then the green-sensitive layer, and last the red-sensitive layer, which sits closest to the base. Light that bounces back off the base reaches the red layer before anything else.

The second is what survives the trip. Blue is absorbed near the top and blocked by the yellow filter. Green is largely used up in the middle. What makes it through to the base and back is mostly long-wavelength light, and the layer waiting for it is the one that records red. In the print or scan, that extra exposure in the red layer shows up as a red halo. Very strong sources push enough light back to register in the green layer as well, which is why the inside of a heavy halo reads orange rather than pure red.

On black-and-white film there is only one kind of emulsion, so halation shows up as a plain white glow. You see it most on old photographs of windows and on film with no anti-halation protection.

The anti-halation layer, remjet, and CineStill

For most of photography's history, halation was a defect. It softens fine detail around every bright edge. So manufacturers build in protection: a light-absorbing layer that stops the light before it can bounce back.

• Still film uses a dyed or grey base, or an anti-halation undercoat between the emulsion and the base. The dye is bleached or washed out during processing, so you never see it on the finished negative.
• Motion-picture film has traditionally used remjet ("removable jet"), a carbon-black backing on the back of the base. It absorbs stray light and also stops static and scratches in a movie camera. It has to be stripped off in the ECN-2 process (see Lomography on remjet). Eastman Kodak has announced it is replacing remjet on its Vision3 range with an anti-halation undercoat (Kosmo Foto, 1 June 2025).

Remjet would contaminate the C-41 chemistry that ordinary labs use. CineStill's answer was to take Kodak motion-picture stock and remove the remjet before selling it, so any lab can develop it. The side effect became the brand: with nothing behind the base to absorb it, bright light bounces back, and every street lamp gets a red halo. CineStill's own FAQ describes it as reflection "inside the film base or off of the pressure plate" onto the red-sensitive layer. That is the look people mean when they search for halation today. We cover it in detail in CineStill 800T on iPhone, halation included.

Why most halation effects look wrong

Search for a halation filter and you'll find plenty. Most of them get one or more of these wrong.

• They glow the highlight itself. Real halation happens around a source that has already gone to white. If the lamp turns pink, the effect is tinting the wrong pixels. The halo belongs on the darker pixels next to the source.
• They glow everything. A blur of the whole image, blended back, is a soft-focus or diffusion effect. Halation only comes from light strong enough to get through the emulsion. Midtones and faces don't halate. There has to be a brightness threshold.
• Wrong colour. A white glow is bloom. A flat, saturated red looks like a filter. Real halation is a warm red-orange that fades out as it spreads, because it's a second, weaker exposure.
• Wrong size. The halo's width is set by the physical thickness of the base, which is fixed. It shouldn't change because you changed the output resolution, and it shouldn't be so wide it fogs half the frame.
• Put in the wrong place in the chain. If the glow is added before the film's tone curve and colour, the curve's highlight shoulder squashes it and shifts its colour, and every film you try changes the halation too. It's more predictable added after the look, where the settings you choose are what you see.

Better tools model the right things. Dehancer's halation for desktop editors has a brightness threshold and profiles for each film format, with and without remjet. On iPhone, mood.camera's 800T-inspired preset includes halation.

How Chobial models halation

In Chobial, halation is part of a film's Effects, next to grain. It follows the physics above, in four steps:

1. Pixels brighter than the Threshold (a luminance level, 50–100%) are isolated. Everything below it produces no halo, so faces and midtones are left alone.
2. That bright-only layer is blurred. Spread sets the radius as a fraction of the frame's short side, so the halo is the same size relative to the picture whatever the resolution.
3. The blurred light is tinted red-orange, because long wavelengths travel furthest.
4. It's screened back onto the photo. A screen blend brightens dark pixels and does almost nothing to pixels that are already white, so the glow shows up on the darker surroundings and the source stays white.

It's applied after the film's Strength dial, like grain: it's part of the stock, not part of the colour. In a monochrome film the glow is neutral at the same brightness, the way it would be on black-and-white film. You see all of it live in the viewfinder while you shoot. Touch and hold the viewfinder to peek at the scene without the film.

The four halation stocks

Pick a Stock first, then adjust Amount, Threshold and Spread on top.

Doing it in Chobial

1. Open Films (hold the film on the camera, or go to Settings › Manage Films), then tap + › New Film and choose a Start From film. Chobial Negative is a good base for night colour. The full walk-through is in Make your own film.
2. In Effects › Halation, pick a Stock. Start with Standard.
3. Check the preview on a night photo from your library. Hold the preview to compare with how the film started.
4. Adjust Threshold until only real light sources glow, then set Spread and Amount.
5. Tap Save. The film is now in the camera's strip, live in the viewfinder, and in the editor for photos you've already taken. Every Chobial photo is a RAW negative, so you can develop old night shots again with the new film.

How much halation is too much?

A little goes a long way. Some checks:

• Look at skin and white clothing. If a white shirt in daylight or a face under a key light is glowing red, the Threshold is too low. Real halation needs light far brighter than a lit subject.
• Look at the source, not just the glow. The halo should be a fringe. If it's wider than the lamp that makes it, lower Spread.
• Daylight is different. On film without remjet, daylight halation shows up mostly where bright sky meets dark branches or rooflines. If a sunny scene looks pink all over, use Subtle, or keep a separate film for night.
• Grain and halation together. They're both parts of the stock. A heavy halo on a grainless, clean image looks pasted on. See why digital grain looks fake.

The effect worked on film because it was an accident of physics, found on the brightest things in the frame and nowhere else. A fake that keeps to that rule is hard to spot. One that puts a red glow on everything is easy to spot.

CineStill is a trademark of CineStill Film. Kodak and Vision3 are trademarks of Eastman Kodak Company. Chobial is not affiliated with either.

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