Techniques on how to add halation in post
The term “Halation” comes from the word “Halo”.
Halation is a visual effect that appears when shooting on film which is an orange halo that tends to occur along the contrasting boundaries of the overexposed areas and around bright light sources.
This effect is more pronounced in the backlit shots and night scenes. Halation is one of the properties unique to analog film stock and isn’t found in digital footage unless modified/simulated in post-production.
The incoming light penetrates blue, green, and red layers of the film stock, then only partially gets absorbed by the anti-halation backing. The strongest rays bounce back into the red layer and create halation.
Halation is actually a defect in film acquisition. This is why most film stocks have backings to reduce it. To combat halation, film manufacturers treat the base of the film to reduce reflections. grey base is a film base permanently dyed a low density grey colour, this reduces reflection back into the emulsion and light-piping within the base. Another way is to introduce an anti-halation layer between base and the emulsion which has the same effect as a dyed base; or the coat the rear surface of the base with an anti-halation layer.
But usually when film print emulation are being used to emulate the colors of the film stock in digital footage, halation is added to give the footage an film look. Halation is most noticeable when the bright object is surrounded by black. When the background gets brighter, the halation is less or not visible. The objects’s brightness determines the luminance and the width of the halo.
Emulating film halation
- Convert the image from the working space curve to linear (gamut stays the same).
- The emulation needs to be processed in scene-linear (gamma 1.0) to represent the flare. This is to cover the maximum part of the highlights or exposed areas. converting the scene to linear from the log helps to easily control the part of highlights.
- With curves, force all except for the super bright spots (the “halo emitters”) to 0. Being in linear light, the curve has to be quite aggressive because the highlights are way outside the usual 0.0-1.0 range (see image).
- Give it the orange tint.
- Blur. The blur amount is the maximum flare width.
- Add the result back to the original (linear) image.
- Convert from linear to working space curve.
(Credits: Matthias Tomasi)
Emulating halation inside Blackmagic DaVinci Resolve.. (without any external plugins)
Update: With the new resolve update 17.4, we now have In-Built Resolve OFX plugin for halation!
Add a node add Color space transform OFX, Convert gamma from current space to Linear gamma – add another node with cst and go linear gamma back to your footage gamma towards the end. In between, add a layer node structure with blend set to add, then on bottom node, create the curve, and in the next serial node’s blur tab and add about 65 blur to red channel and 60 to green balance and adjust accordingly.