When printing view ports in the Layout area and in Print Preview, the High Quality Printing option is enabled by default. A mixed process is used for printing: visible lines, edges, dots, hatching and fonts are based on vectors. With vector printing, these elements remain sharp, even when greatly enlarged. Colors and textures are printed as images.

Select images with a suitable size (for example 2048×2048 pixels).
If you use high-resolution images as textures, set the Texture Quality to Extra High.