The Maximum Blur filter broadens highlight regions in the image, and shrinks darker areas. It works by comparing each pixel to its neighbour and replaces darker pixels with lighter pixels. This is most useful for modifying masks.
About the Maximum Blur filter
This filter can be applied as a non-destructive, live filter. It can be found in the Filters menu, in the Blur category.
Settings
The following settings can be adjusted in the filter dialog:
Radius—controls the intensity of the filter. Type directly in the text box or drag the slider to set the value. Dragging to the right on the page allows you to override the maximum value—values above 100 px may affect performance so use with care.
Circular—if this option is off (default), highlight regions expand to form square areas. When selected, expanded highlight regions are circular.