This option maximizes the KView window and the currently shown image so you can have a closer look at it. Even the window decorations (titlebar etc) are temporarily removed. Selecting this option once again switches back to normal mode.
If you have selected any part of the image (by drawing a box around it using your mouse) you can cut off all the rest around it by using this option. Your image is effectively reduced to your selection.
Resets the image to its original state (right after opening it).