magnitude spectrum

How much of each frequency is present in an image, independent of where it sits.

The magnitude spectrum $|F(u,v)|=\sqrt{\operatorname{Re}(F(u,v))^2+\operatorname{Im}(F(u,v))^2}$ reports how strongly each frequency $(u,v)$ is present in an image, unaffected by shifting the corresponding pattern to a different position -- the companion phase spectrum carries the position information magnitude discards.