Preview Not Rendering Images Properly
As per the discussion above, changing the scaling to the default setting and back seems to fix the issue.
Screen scaling a Retina MBP brings up a lot of issues when running on Integrated GPU (Intel HD or Intel iris) as it hogs the system memory. If you have a dedicated GPU on the MacBook Pro, turn off the automatic GPU switching(System Preferences -> Energy Saver) which will reduce these issues when scaling the screen from it's default resolution.
If you only have Integrated GPU, Try running on default scaling when running memory intensive tasks.
