I have an image I made for a desktop background at 1920x1080.
I want to print it out, but it’s only 72dpi.
In photoshop a 72dpi image at 1920x1080 is 15" high and 26.6" wide.
Doesn’t that mean it should print in full quality on a 15"x26.6" sheet of paper? Regardless of the DPI?
Your background is 72PPI and not necessarily 72DPI. Pixels on the screen do not equal dots on the printer. If you can find a printer capable of printing at 72DPI then your image would be that big but more likely the printer will use 300DPI as its lowest resolution and may go as high as 1200DPI. If you were to print it at 15"x26.6" on a 1200DPI printer then each pixel of the original will get about 277 dots used to display it. At full quality on such a printer with only one dot per pixel it would be 0.9" high and 1.6" wide. On a 300DPI printer it would be 3.6" high and 4.4" wide.