Halation

Halation is the warm glow that wraps bright sources on film: the bloom around a practical lamp, the red edge on backlit hair, the way a window burns into the wall beside it. Unlike a lens flare or a glow filter, it happens inside the film: light went all the way through the emulsion, reflected and scattered back at the interface between the emulsion and the film base, and exposed the layers a second time on the way out. Film/Emulsion™ models the visible consequences of that round trip, and the Halation tab is where you set how much of it your film lets through.

What is happening in the film

In the simplest description, color negative film is three light-sensitive records stacked on a clear base, blue-sensitive on top, then green, then red at the bottom, nearest the base. Most of the light from a scene is absorbed in those layers on the way in. Where a source is bright enough, some light gets through all three, reaches the base, and reflects back up from the interface between base and emulsion. On the way out it exposes the layers again, but now spread sideways, so it lands in a ring around the source rather than on it.

Two things follow from the geometry. The red layer is the first one the returning light meets and the one it exposes most, so the halo is red. If the source is bright enough for the returning light to reach the green layer as well, the halo shifts from red toward orange. And because only strong light makes the round trip, halation has a threshold: it appears around highlights and specular sources, not across the whole frame.

Film manufacturers spend a great deal of effort suppressing this. An anti-halation layer exists to absorb the light before it can reflect, and Kodak documents three ways to do it: remjet, a black carbon coating on the back of the film that is washed off at the start of processing; an anti-halation undercoat, a gelatin layer directly under the emulsion whose color is destroyed during processing; and a neutral-density dye carried in the film base itself. Kodak’s documented 2025 construction replaces remjet with an anti-halation undercoat. Remove the backing entirely and halation increases substantially. The strength of the anti-halation layer goes a long way toward setting how much halation a stock shows.

The halo also depends on the format. Its apparent radius scales inversely with the size of the frame: a Super 8 frame is a small fraction of the size of a 35mm frame, so the same halo covers far more of the picture. Small gauges look more heavily halated because the halo covers more of the frame; 65mm shows far less of it for the same reason.

On real film, halation also costs sharpness, because the same back-scattered light softens the whole image a little. Film/Emulsion™ renders the visible halo on this tab. Irradiation moves a little energy from the source into a tight bloom, but there is no overall softening here. If you want the accompanying softness, the Grain tab carries its own resolution model (Bind Image to Emulsion and Generational Loss), which you set independently. (The Texture guide is coming later.)

Simple and Advanced

The Halation tab has two modes, set by the Mode menu.

Simple gives you two sliders, Amount and Character, that drive the complete halation engine underneath. Nothing is switched off in Simple mode. The two sliders drive a curated mapping onto every mode-specific Advanced parameter and the backing, so the four Advanced controls and the backing type move together. Film Gauge stays independent. It is not driven by the two sliders.

Advanced exposes the model’s detailed halation parameters: the reflection strength, the scatter distance, the layer crosstalk, and the irradiation, alongside the gauge and the backing type.

You can switch between them freely. Going from Simple to Advanced keeps the halo you had and shows you the parameters that make it. Going from Advanced to Simple derives Amount and Character from your reflection, scatter, and backing and re-applies the mapping. If you had set an unusual combination by hand (a high crosstalk or irradiation the two sliders cannot reach, say), that projection can change the halo materially, because those hand-set values are overwritten by the mapping.

Every Film Look preset sets this tab as part of its recipe. The backing, gauge, reflection, scatter, crosstalk, and irradiation for a stock are stored with the look, so a preset arrives with the halation its stock would show before you touch a slider. If the tab is in Simple mode when a preset loads, Amount and Character move to show the recipe you just loaded. Most presets sit outside what the two sliders can express, and for those the tab switches itself to Advanced rather than show you sliders that do not match the halo on screen.

Start in Simple. Move to Advanced when you want to pull one variable on its own.

Opacity

Opacity blends the complete halation result against the image without it. It is a wet/dry control on the whole stage, not a strength control on the halo: the halo is still shaped by Amount and Character, or by the Advanced parameters, and Opacity fades the finished result in or out. Use it when a look is right but there is simply too much of it, and use Amount when the halo itself needs to be weaker.

Simple mode

Amount

Amount sets the strength of the reflection halo: how much of the returning light the model lets back into the image. It scales the reflection strength and nothing else, so the size of the halo and the Irradiation term stay where Character and the gauge put them. The brightness a source needs before it halates, the threshold, is set by the Quality mode, not by Amount. The midpoint is the plugin’s default. Below it every halo dims together. Above it every halo gets brighter.

Character

Character describes what kind of halo you get, from a tight modern red halo at the left end to a big warm vintage glow at the right. Underneath, the slider is walking through the three anti-halation backing types in order, from a modern remjet stock, through an older dye-backed stock, to a stock with no backing at all, and adjusting the scatter distance and reflection strength to match each one.

Across the left half, the halo stays tight, mostly red, and close to the source. Past the midpoint it starts to warm toward orange and to bloom at its core, because past the midpoint the slider also raises Emulsion Crosstalk and Irradiation, which tints the halo from red toward orange and blooms its core, the way a stock that is not protecting itself behaves. The right end is a stock with no backing at all: a big, warm, soft halo.

The midpoint is the default and the neutral setting. Amount and Character at their midpoints correspond to the halation look the plugin ships with when no preset is applied.

Advanced mode

Advanced mode replaces Amount and Character with four percentages. Reflection and Base Scatter are multipliers on the backing’s own values, with the backing’s value at 100%. Emulsion Crosstalk and Irradiation are direct amounts. Irradiation’s zero is truly none; Emulsion Crosstalk’s zero is the model’s minimum rather than none, because a little green-layer exposure always survives.

Reflection

Reflection (%) multiplies how much light reflects off the film base. It is the closest thing to a pure strength control: raise it and every halo gets brighter without getting larger. The base value comes from the backing you have chosen, so 100% means the model’s value for that backing.

Base Scatter

Base Scatter (%) multiplies the model’s lateral spread radius, how far sideways the returning light is modeled to spread before it re-enters the emulsion. It sets the size of the halo. Raise it for a wider, softer bloom. Lower it for a tight edge glow. Like Reflection, the base value comes from the backing, and Film Gauge then scales the result to the frame.

Emulsion Crosstalk

Emulsion Crosstalk (%) controls how much of the returning light reaches the green layer. At zero the halo is at its reddest, with only a trace of warmth. Pure red is not reachable, because a little green-layer exposure always survives. As you raise it, more green bleeds in and the halo warms toward orange. This is the color control for the halo. There is no separate hue or RGB balance, because the color of real halation is decided by which layers the returning light reaches, and this slider stands in for that.

Irradiation

Irradiation (%) is the model’s tight core-bloom term, separate from the base reflection. It stands in for light scattering sideways within the emulsion itself, before it ever reaches the base, and it shows up as a bright core bloom on the edges of hot sources rather than a wide halo. Keep it low. A few percent adds a hot edge to speculars. The top of the range is for deliberate effect.

Film Gauge

Film Gauge sets the physical size of the frame, from 8mm to IMAX. A smaller gauge produces a larger halo relative to the frame, since the same halo covers a smaller picture. Switching a 35mm look to Super 16 makes the halation larger relative to the frame without touching any other control, and moving to 65mm makes it much smaller.

Film Gauge is also on the Grain tab. The two are independent, so you can size the halation for one gauge and the grain for another if a look calls for it, but for a conventional matched-stock setup keep them the same.

Anti-Halation Backing

Anti-Halation Backing picks which of three model backings the halo is built from, and with it the base reflection coefficient and the base scatter distance that the Advanced percentages multiply. Each is named for the real backing it stands in for.

• Modern Remjet. A carbon backing that absorbs most of the light before it can reflect. Tight, faint, red halo. Modeled on a remjet-backed camera negative.
• Vintage Dye. A dye layer instead of carbon: absorbs less, scatters further. A larger, brighter halo than Modern Remjet. Its warmth is not from the backing. Like the others, the halo’s color comes from Emulsion Crosstalk, which you set separately. This is the plugin’s default.
• No Backing. No modeled anti-halation backing: the highest reflection and widest scatter the model offers, for the biggest, brightest halo it produces. Its color still comes from Emulsion Crosstalk, which you set separately.

In Simple mode the Character slider chooses the backing for you. In Advanced mode you choose it here. Reflection and Base Scatter then work relative to the backing you pick; Emulsion Crosstalk and Irradiation are direct amounts that do not depend on it.

Controls

Working with halation

• Judge it with grain on. A halo rendered over a clean image tends to read as a glow filter rather than as film. Keep the Grain stage enabled while you set halation, even at low opacity.
• Judge it on the right shots. Halation only shows around sources bright enough to cross the threshold. A flat interior with no practicals will not tell you anything. Find the shot with a window, a lamp, or backlit hair and set it there.
• Reach for Amount before Opacity. Amount changes how the film behaves. Opacity fades the result. If the halo is too wide or too warm, Character or the Advanced parameters are the fix, not Opacity.
• Match the gauge to the stock. Set the gauge once, the same on Halation and Grain, and leave it. It is part of what makes a 16mm look read as 16mm.
• Halation is not sharpening. If the image feels soft or too crisp, the resolution controls live on the Grain tab, and they act on their own.

What the Halation tab cannot do

There is no separate sharpness control on this stage. The halo’s edge is set by Base Scatter and Irradiation, and also shaped by the Anti-Halation Backing, Film Gauge, and Quality settings. Overall image resolution is modeled on the Grain tab, and it does not read the halation settings.

There is no hue or RGB balance for the halo. Classical base-backscatter halation, the round trip this model renders, is red or orange, and the model produces those colors from its layer coefficients. Emulsion Crosstalk is the whole color range, apart from the neutral halo the black-and-white presets switch on. Some stocks show a separate blue-layer scatter that can look similar, but that is not classical halation, and the plugin does not model it.

Halation renders after the print stage, over the finished image. The plugin does not currently model the separate halation a print stock adds during printing.

The description of what happens inside the film follows Kodak’s published film-structure literature, in particular the Essential Reference Guide for Filmmakers section on antihalation backing.

Next: Texture will cover the other half of film texture, the Grain tab: stock, gauge, layer separation, and scanner noise (coming later).