Better Image Viewer adds the following actions: Scroll up/keyboard plus: zoom in Scroll down/keyboard minus: zoom out Keyboard zero: zoom 1:1 Click: toggle between zoom-to-fit and 1:1 Drag: pan Shift+drag: drag image (e.g. to another window) You can also use a popup toolbar on the left-hand side of the window to control zoom. Better Image Viewer is no longer maintained.