Me and I think most other users often like to toggle in the image view mode between fitting the image to window and zoom 100% for analysing. I think this is one of the most frequent actions at all. I like to suggest to define the "Z" key for toggling between these two zoom values. The existing keys "/" and "*" for that are very cumbersome to bear in mind and very inconvenient. One single key just for toggling is much faster (in a german keyboard even the shift key is necessary for both). And finally it would perfectly complete the set of existing toggling keys "Enter" and "F" for navigation between the most important views and modes.
If the actual image neither fits into the window nor zoom is 100% I would suggest the "Z" key fitting the image into the window (large only, otherwise 100%). This way "Z" would provide a comfortable reset to the usual default zoom value for instance after manual changing the zoom factor.
This way XnView would become more perfect as it already actually is
