I got a new PC yesterday and temporarily had Picasa as my default image viewer. This morning when an image displayed, I wanted to look at it in XnView, and so I had the same image displayed in both Picasa and XnView on the screen at the same time. I was quite distressed to see that this image (a 25K PNG file) was much clearer in Picasa than in XnView. I made sure they were the same display size, moved the image around the screen, did everything I could think of to eliminate differences. But regardless of what I did, the Picasa display was much better than XnView's. Here's the comparison:

I hope this is helpful info and can be used to improve XnView's display.