Quote - [But professionals know that if they have a 1200 DPI printer, they don't feed it 1200 PPI images: they know that the printer uses 4 dots to reproduce each pixel, so they know anything higher than 300 PPI is overkill.

Probably the printer will use even more than 4 dots. A square of 4x4 dots of black ink on white paper gives you only 16 shades of gray.