Operator

Dilation by a square
Erosion by a square
Closing by a square
Opening by a square
OCCO with a square

Frame

RGB basis
Saturation invariant frame
Hue invariant frame
Saturation and hue invariant frame
Rotation invariant frame

Based on SVG filter definitions:
Saturation invariant frame
Hue invariant frame
Saturation and hue invariant frame

Colour management

Use linearRGB instead of sRGB (gamma correction).
Clip colour channels independently.
Clip colour channels in the direction of the centroid.