Run dilation, erosion, open, close or gradient over every frame of a clip. On footage the jobs are the ones an editor does with a matte: trimming the fringe off a key, filling pinholes in a mask, thickening the strokes of animated line art, or pulling an outline from a frame.
Masks and keyed clips
With Work on set to Transparency the step works on the alpha of each frame, so it belongs after a key. Open removes specks the key left in the screen, close fills holes in the subject, and a small erode trims the semi-transparent fringe along hair and shoulders. Grown pixels take the colour of the nearest covered pixel, so a dilated edge is the subject’s own colour.
This tool runs one step on one file; to run it after a key in one pass, build the chain in the video workflow.
Line art and threshold
On a scanned or animated drawing, Erode makes dark lines thicker and Dilate thinner, since the dark areas are what grow. The black-and-white mode binarises each frame at the threshold first, which steadies lines whose grey level drifts between frames.
Colour channels
In the default mode each channel is filtered on its own, which is what an editor’s Maximum and Minimum filters do. On footage it spreads highlights or shadows into their surroundings, a blocky, painterly look that is stable from frame to frame because the operation has no random element.
Cost
Around a third of a second per 720p frame on a laptop core, at any radius. Set the export size before exporting a long clip at 4K.