Sometimes, you might want to
switch between an annotation from polygon to mask or vice versa.
Polygons tend to be easier to edit so if you have an annotation that is
in mask-form and you want to edit it, you can convert it by pressing
this button:
When you have selected one or more masks, click the "Convert to Polygon" to change their types
The same can be done in reverse by selecting polygons and then clicking "Convert to mask"