I made something that can help visualize how many MP is needed to make a high resolution prints or view the image on a screen. 150 DPI requires to focus very close
FIX: Very Small Fonts in High DPI 4Κ Monitors in Windows 10. - wintips.org - Windows Tips & How-tos
DPI scaling settings on Windows (HiDPI display) | EIZO
Windows 8.1 DPI Scaling Enhancements to Optimize New Crop of Amazing 4K Displays | HotHardware
Support for high DPI displays - ParaView Support - ParaView
How Pixel Density Works in the Age of 4K | EIZO
Designer's guide to DPI
xorg - Adapt Ubuntu to a high-DPI resolution screen - Ask Ubuntu
OC] Summer Sunset 4K (3840x2160) | 4k wallpapers for pc, Wallpaper pc, Red wallpaper