Why do my hardest images still come out with artifacts?

You have come a long way. Most of your work is clean now, and that is no small thing. What is left is the hard edge of the craft, the difficult cases where artifacts creep in no matter what you do. Those cases feel like failure, but they are actually where real skill is built.\nThe truth is that the tricky cases defeat almost everyone at first. They are supposed to be hard. If they were easy, they would not be the ones that separate a good technician from a great one. The artifacts you are fighting have causes, and each one you trace back teaches you something the easy cases never could.\nSo change how you treat the hard ones. Keep a simple record: what the case was, what went wrong, what you tried. Over weeks you will start to see patterns, and the patterns are the skill. You are not stuck. You are standing at the last and steepest part of the climb, which means you are close.