The window serves for image previewing. For transition into the full screen operation, you can use the combination: Alt+ Enter.
The possibilities of window preview:
Hot keys:
Alt + Enter - full screen mode / normal mode
Ctrl + Q - select tool bar alignment mode: top, left, bottom, right
Ctrl + Shift + T - show / hide toolbar
Enter - return to the file manager and select the current image
Esc - return to the file manager or quit the slide show
Spacebar, Alt + S - play / stop slide show
Backspace, Page Up, Left arrow - display the previous image
in image sequence
Page Down, Right arrow - display the next image in image sequence
Home - first image in image sequence
End - last image in image sequence
Alt + G - go to image #...
Ctrl + P - print current image
Ctrl + 1, Ctrl + 2, Ctrl + 3 - change view mode
Minus sign (-) - zoom out
Plus sign on the numeric keypad, or Equal sign - zoom in
Asterisk - zoom to fit window
Forward slash - zoom 100%
1..9 - zoom 100%...900%