ABSTRACT
The physical meaning of the function value and variables is arbitrary. In the present context, such a function is usually interpreted as spatially variable brightness (or gray-scale degree) of a planar still image, dependent on the position determined by the two coordinates
x, y
forming the position vector
r
=
(
x
,
y
). With respect to the interpretation of variables, the function is often denoted as a spatial-domain function. Theoretically, it is possible to consider spatially unlimited images, covering the complete infinite plane (
x
,
y
); practically, however, image
f x y( , ).
