01-20-2017, 11:47 PM 
	
	
	
		The Levels tool (and therefore the histogram) is restricted to the selection, and is "alpha-weigthed" (ie, pixels contribute proportionally to their opacity). I get this kind of empty display if the selection includes only transparent pixels...  The Histogram display works the same way, so do you have visible histogram in it?
	
	
	
	

 

 
