What is the difference between PMax and DMap?
PMax is a “pyramid” method. It is very good at finding and preserving detail even in low contrast or slightly blurred areas. It's also very good at handling overlapping structures like mats of hair and crisscrossing bristles, nicely avoiding the loss-of-detail halos typical of other stacking programs. But PMax tends to increase noise and contrast, it can alter colors somewhat, and it's liable to produce fuzzy “inversion halos” around strongly contrasting objects.
DMap is a “depth map” method. It does a better job keeping the original smoothness and colors, but it's not as good at finding and preserving detail.
The two methods complement each other. Some types of subjects look good when they are processed automatically by PMax, but not by DMap. Other subjects are just the opposite. For particularly challenging subjects like bugs and flowers shot through microscope objectives, neither method is ideal by itself. In that case the best results are obtained by using human judgment and the retouching tool to combine the best aspects of both algorithms.
For further discussion of these issues, see “DMap versus PMax” on the Zerene Stacker: How To Use It page.