Mixed Bit Depths and Compander

Mixed Bit Depths and Compander

Most effects don’t, alas, support 32 bpc, although there
are dozens that do. Apply a 16 bpc or (shudder) 8 bpc
effect, however, and the overbrights in your 32 bpc project
disappear—all clipped to 1.0. Any effect will reduce the
image being piped through it to its own color space limitations.
A small warning sign appears next to the effect to
remind you that it does not support the current bit depth.
You may even see a warning explaining the dangers of
applying this effect.
Of course, this doesn’t mean you need to avoid these
effects to work in 32 bpc. It may mean you have to cheat,
and After Effects includes a preset allowing you to do just
that: Compress-Expand Dynamic Range (contained in
Effects & Presets > Animation Presets > Image – Utilities.
Make certain Show Animation Presets is checked in the
panel menu).
This preset actually consists of two instances of the HDR
Compander effect, which was specifi cally designed to
bring fl oating point values back into LDR range. The fi rst
instance is automatically renamed Compress, and the second,
Expand, which is how the corresponding modes are
set. You set the Gain of Compress to whatever is the brightest
overbright value you wish to preserve, up to 100. The
values are then compressed into LDR range, allowing you
to apply your LDR effect. The Gain (as well as Gamma) of
Expand is linked via an expression to Compress so that the
values round-trip back to HDR.
Additionally, there are smart ways to set up a project to
ensure that Compander plays the minimal possible role. As
much as possible, group all of your LDR effects together,
and keep them away from the layers that use blending
modes where fl oat values are most essential. For example,
apply an LDR effect via a separate adjustment layer instead
of directly on a layer with a blending mode. Also, if possible,
apply the LDR effects fi rst, then boost the result.

into HDR range to apply any additional 32 bpc effects and
blending modes