Hi Fishrrman. I am on a 2012 iMac up to date with OS X El Capitan, 3.4 GHz Intel Core i7 with 16 GB 1600 MHz DDR3 Memory. Graphics: NVIDIA GeForce GTX 680MX 2048 MB. 27" Screen. It has worked fine until the last 3 days. I have noticed however if I zoom in and out on the image opened in preview that at some zooms the weird pixelation disappears and then at another comes back again. Cannot figure out if this is a hardware or software problem. Have not installed anything new in the past 2 weeks. Any thoughts?
I run a parallels windows desktop but without much on it. When I open the image in Windows Picture Viewer the image is fine.