I've done some testing and found that Pixelmator is giving me banding on gradients (same issue in Photoshop and Illustrator, too). I don't think it's specific to Pixelmator, but I need to get to the bottom of what's causing this. After some initial testing, it appears that when I previewa pdf, tiff or .ai file in Quicklook, it shows the gradient smooth, without banding, which I'm sure is the OS doing proper dithering, etc. Same thing most of the time when opening files with gradients in Preview.app. The reason for stating this is that I wanted to rule out the graphics card or any hardware related issues first - the issue is NOT hardware related. I've had some friends test this on other macs (w/ better graphics cards) and got similar results. I'm currently running a 2012 Mac mini with OS X El Capitan 10.11.1, HD4000 graphics card, 8G ram.
I basically just wanted to know the specs for how Pixelmator renders gradients and how to reduce or hopefully remove banding all together. Any ideas? Thanks in advance.