Horizon leveling in post
Also known as: post horizon correction, levelling afterwards
Straightening a tilted horizon after filming by rotating each frame, which works well on small errors and crops the frame to do it.
Updated
What it means
Levelling afterwards rotates the picture so the horizon sits flat. The rotation is applied per frame, so a camera that drifted through a shot can be corrected continuously rather than by one fixed angle.
It is the editing equivalent of what a camera does live. Where Horizon Lock holds the frame level while recording, this does the same arithmetic later from whatever was actually captured.
The difference is what is available to work with. A camera correcting live can use its own motion sensors, while a correction afterwards has either the recorded telemetry or nothing but the pixels.
How it works in practice
Telemetry makes it far more accurate, which is why GPMF telemetry matters here. A camera that recorded its own orientation gives the correction an exact angle rather than one inferred from the picture.
Correcting a continuous drift beats correcting a fixed tilt, because a mount that shifted during a run needs an angle that changes rather than one average value applied throughout.
Deciding how much to correct is editorial rather than technical. Full levelling can look oddly static on footage that was genuinely leaning into a turn, and a partial correction often reads more honestly than a perfect one.
What to watch out for
Every rotation crops, and the crop grows with the angle. A camera ten degrees out loses noticeably more frame than one two degrees out, which stacks with any Stabilization crop already applied.
Large corrections also reveal the cropping as movement. Edges that creep in and out across a shot are more distracting than the tilt they replaced.
Correcting a fisheye frame without accounting for its geometry produces a bowed horizon rather than a level one, so Fisheye correction and levelling have to be considered together rather than applied in whichever order is convenient. Correcting geometry first and rotating second is the order that behaves predictably.
How RawClip handles it
Clips are scored in the orientation they arrived in, because rotating first would crop the frame and change what the analysis actually sees. A noticeably tilted shot is weighted down on framing rather than silently straightened, since correcting it is a decision that visibly shrinks the frame.