The Magnify tool is used to zoom in or out of an image. By default the tool will zoom in when clicked. By holding Ctrl this behavior can be changed to zooming out.
This option toggles whether or not the image view window will resize to match the new image magnification level. When this option is not set, the window will remain at it's current size regardless of the magnification level.
The Tool Toggle section can be used to manually toggle between zooming in or zooming out of the image.
Default Keyboard Shortcut: Shift-M
Ctrl toggles between zooming in or zooming out.