I've been annoyed today and last night when the Preview app that I have used constantly for the last few years has all of a sudden been acting up, with no real instigating factor that I can think of. I will be reading a book in a crystal-clear resolution and then all of a sudden the next page will be super blurry and unreadable. After I close the app and open it up again, the resolution is marred, not solely on the book in question, but on everything I can open in Preview. I have to restart my MacBook 2013 Retina in order to restore the vibrancy of the text in my Preview app, but then the problem usually happens again after a couple of hours. Can someone tell me how to stop this nuisance?