Mark, Are you defining a preview of dark sky for MaskedStretch background reference? And are you setting the target background high enough? The most apparent issue, and surprised no one commented- the processed images are clearly clipped as evidenced by an unnaturally dark background. Your dimmer detail is simply discarded. Perhaps this was intentional, but when compared with your great looking AutoStretch, you're losing a lot of data. I much prefer HistogramTransformation for the initial stretch. Get a great STF AutoStretch visualization, then transfer that to HT for an excellent stretch. Good advice here by everyone!