Hmm, another idea has just come to my mind.
What if a user, for any purpose, wanted to 'Spotlight'
multiple areas of a picture like I made this:
source of photo: http://www.apartments-liverpool.co.uk
application used to make 'spotlight': Paint.NET v3.55 wi/ 2nd black filled Layer, adjusted opacity + selection
1.) To perfom such multiple spotlighting, should we have a hotkey control like Shift+left-click select area's (select multiple areas) ----> to select multiple area's during this spotlight mode and then to press 'ok' for all non-selected area's to be adjusted in this spotlight mode
2.) So should 'spotlight' be named 'Spotlight mode' [in English] in where it would enter a special mode in the xnview Viewer.
3.) Would this feature take up a lot of memory while in use. I hope not and really it should not, except if the picture's dimensions are really huge (e.g. 4000x4000)
Perhaps, later, the ability to use other selection-shapes common in picture graphic editors such as 'circle', 'oval', 'triangle' and even 'freehand lasso' ;
http://newsgroup.xnview.com/viewtopic.php?f=34&t=19288 - could make a 'Spotlight' much more interesting and even preciser in the long run.
4.) What about setting a 'background color' for the non-spotlight areas.. hmmm..

Could come in handy especially for old black+white photograph's
5.) This 'Spotlight' feature would have so many helpful uses if implemented into XnView

Think about 'spotlighting' yourself or other friends in a school class photograph
6.) So in summary for xnview , the 'spotlight' could entail (not at first, but fully later):
-opacity (of non-spotlighted area of picture)
-adjust brightness/contrast (of non-spotlighted area of picture)
-average blur (of the picture itself)
-background color (of non-spotlighted area of picture)
-hue/saturation of same background color
-drop shadow that surrounds each spotlight.. Sooner or later version?)
....All of these things XnView can already do itself in other places of the app, just never existed all at the same time within one fucntion.