Flicker removal
Also known as: deflicker, flicker reduction
Evening out brightness that pulses from frame to frame, usually caused by artificial light or by exposure changing during a time-lapse.
Updated
What it means
Flicker is a brightness difference between neighbouring frames. The eye reads it as pulsing even when each individual frame is correctly exposed. A still from the clip looks perfect.
Two causes dominate. Artificial lighting cycling at mains frequency against a mismatched Shutter speed, and automatic exposure adjusting between the frames of a Time-lapse. One is physics, the other is a setting.
LED lighting is the modern version. Many fixtures dim by switching rapidly, which produces banding and flicker that no shutter choice fully removes. Gym and stadium lighting are the usual offenders.
How it works in practice
Prevention is almost entirely a shutter question. Matching shutter to the mains frequency removes the mains case, and locking exposure removes the other. Both are decisions made before recording.
Exposure lock before the first frame is what makes a sequence consistent, which matters more on a long interval than any correction afterwards. A locked value is worth more than a clever tool.
Where it has to be fixed, the tool averages across frames. A deflicker pass measures brightness over time and smooths the curve, which works well on a steady shot and poorly on a moving one, where the brightness is genuinely changing.
What to watch out for
Smoothing brightness also smooths intent. A real change in light, a cloud passing or a rider entering shade, gets flattened along with the flicker. The result looks oddly inert.
Rolling shutter turns flicker into bands. A Rolling shutter sensor under cycling light records different brightness across the frame, and a temporal fix cannot help a spatial problem. Two failures wear one name.
It also interacts badly with grading. Correcting flicker after a heavy grade is harder, because Curves have already changed the brightness relationship the tool is trying to measure.
How RawClip handles it
Clips are evened out for brightness while the sequence is assembled, which handles the mild cases that come from automatic exposure. Footage with heavy flicker from artificial light loses to cleaner coverage of the same moment, because the problem is inside every frame rather than in the sequence of them.