What causes blurry images on a Macbook?

Question

macbook

Briefly about the problem.
Recently, I encountered the problem of a slight freeze on the macbook, namely, the screen froze for 30 seconds, and sometimes everything froze, except for the mouse cursor, i.e. they could be moved, but nothing was pressed. A couple of times it happened, the macbook completely hung up and only a forced reboot saved it.
Contacted Apple. Under their guidance, the macbook was completely cleaned and the system was installed.
We agreed that I work on an old version of Os X for a week and do not update to see if the problem will occur on the old operating system.
There were no freezes yet, but a new problem was discovered. Namely, when I open a photo through a standard viewer, it often happens that the photo opens in a blurry form. And, interestingly, if I turn off the viewer or switch cmd + tab to other programs, and then open the photo viewer again, the problem remains. And if in the viewer I zoom out or zoom in and return to the original, then the picture quality becomes good.
Mac is only a year old, I don’t understand what is happening, please give advice.
I took it to the service under warranty, they diagnosed the iron in 20 minutes, they said there were no problems.

Answer 1

Try to put a program like www.xnview.com/en/xnviewmp to view photos and see if the blur persists there too?

Answer 2

This is normal behavior when resources are low. What Mac do you have? What photos do you open? How many apps are running?