Dmax = -log10(minimum print reflectivity) is a measure of the deepest black tone a display or printer/ink/paper combination can reproduce. It is an extremely important quality factor. Images with poor Dmax look pale and weak. Dmax = 1.7 is a good value for matte prints; 2.0 is a good value for glossy, semigloss, and luster prints. There have been reports that Epson Ultrachrome K3 printers have Dmax as high as 2.3 with Premium Luster paper. That would be outstanding.
Dmax is affected by the printer, paper, and ink. The response curve is also affected by the ICC profile. Print Test can help with the selection of supplies and diagnosis of printing problems.