JSON format:

global object MUST consist field "Z" or "maskz" with Z-coordinate of mask

it CAN contain global fields (common to all holes) such as in holes array
its field bbox (if exists) HAVE TO BE GLOBAL convex bbox of all holes!

it MUST contain at least one hole object (or hole array)

fields of "hole":
	"shape"  - shape of hole (could be "square" and "round" or "ellipse")
	"radius" - scalar or array[2] with radius parameter
	"center" - array[2] with coordinates of hole's center
	"bbox"   - array[4] with bounding box of a hole
	
	independently from shape any hole can consist both fields "radius" and "center" or single field "bbox"