Dewarping
Also known as: warp correction, geometry correction
Correcting geometric distortion in a frame, whether from the lens, from rolling shutter or from aggressive electronic stabilisation.
Updated
What it means
Dewarping is the general term for pushing a distorted image back towards correct geometry. Lens curvature is one source, but so are sensor readout effects and the warping that stabilisation introduces on its own.
It overlaps with Defishing without being the same thing. Defishing addresses a known lens projection, while dewarping covers any distortion including the irregular kind that varies from frame to frame.
The frame by frame variation is what makes it harder. A lens distorts identically in every frame and can be corrected with one map, while Rolling shutter skew depends on how fast the camera was moving at that instant.
How it works in practice
Lens correction comes first because it is predictable, and the remaining irregular distortion is then addressed against what the stabilisation and telemetry say the camera was doing.
Telemetry makes the second pass considerably more accurate than guesswork. A camera that recorded its own motion through GPMF telemetry gives a correction tool the information it would otherwise have to infer from pixels.
Correcting less is usually better. A partially dewarped frame that still bends slightly reads as natural, while a fully corrected one often reveals the stretching the correction needed to do.
What to watch out for
Every correction crops, and corrections stack. Lens correction followed by stabilisation followed by dewarping can leave a noticeably tighter frame than the original was shot at.
Over correction produces its own artefacts. Edges that wobble, straight lines that bow the other way and corners that stretch are all signs of a map pushed harder than the footage supports.
Applying it inconsistently across a session is the editorial mistake, since geometry becomes a visible difference between shots that should have cut together invisibly. A Rough cut reveals it faster than inspecting clips one at a time.
How RawClip handles it
Clips are analysed in the geometry they arrived in, because correcting first would crop the frame and change what the analysis sees. Distortion is treated as a characteristic of the footage rather than as a fault to be fixed before scoring.