Click an arbitrary position on the image.
A rotatable rectangular window centered on that position will appear.
Move the control points of the window on the image to adjust the position and size of the rectangular mask.
Click [UNDO] to cancel the previous operation.
Click [DRAW].
The rectangular mask is drawn and filled in.
If you click [ERASE], the mask is erased in the configured rectangular shape.
Click [OK]. The rectangle setup is complete.
Clicking [CANCEL] will cancel the setup.