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Tip: Linear Blending at Any Color Depth in After Effects

This tip is on the high-end of the scale for After Effects artists. If you like working in linear floating point 32-bit HDR because of the “linear” part - where images do not have a video gamma applied before being composited, so that, for example, Add mode actually works properly - you can have it without being in 32-bit.

This tip, alas, is already only for those who already enjoy and appreciate the benefits of working in 32-bit linear HDR but sometimes would like to drop down to 8 or 16 bit while working to go faster (and then return to 32-bit mode to render). If you are not already working this way, explaining why you would want to do so goes way beyond a tip. It requires at least one chapter of a whole book.

Anyhow. here’s what you actually do: go into File > Project Settings and check Blend Colors Using 1.0 Gamma - that’s it. Notice that this option is available at all bit depths.

The option is grayed out if you choose a Working Space and check Linearize Working Space; in that case, the entire working space, not just the blends, is linear (so solids and other colors you might set also behave linearly, with middle gray at around 18%). That also works at all bit depths.

There is so much confusion about color Working Spaces, linear color and linear blending that most people mash the three together, but in the After Effects model they operate independently. A Rec. 709 Working Space can be linearized, or it can have a video gamma but blend with a linear 1.0 gamma.

What difference does this actually make? It means that Add and Multiply modes, the most fundamental compositing blending modes in a linear world, are not broken outside of 32 bpc linear HDR. You can comp fire into a shot with Add mode and not have to compensate for it looking horrible even in 8 bpc.

Detail of a comp with linear blending off (left) and on (right). Without it, the fire highlights are clipped and the subtle smoke nearly disappears.

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