DPI, or dots per inch, is a measurement used for printer resolution. But DPI is also used when referring, somewhat inappropriately, to scanners, monitors, and digital cameras.
The DPI specification when you look at printers, expresses the number of dots in every inch a printer can print in order to form text or graphics. Higher DPI means text that looks more refined. The same goes for images – it will look crisper with a higher DPI. In order to save on ink, low DPI is used when printing draft copies. Often, a DPI of 150 or 300 is used for this purpose. High resolution DPI starts at 600 for standard printers. Higher DPIs are often seen on color printers that have been specifically designed to print digital photography or other images that are in high resolution.
With regards to monitors, the DPI refers to the amount of pixels that can fit per inch in a display screen. Technically, the correct term should be PPI or pixels per inch, but DPI is used more commonly. A computer monitor display setting that has 1280 x 1024 will have 1.3 DPI, while a setting of 800 x 600 will have a DPI of 480,000.
Scanners also perform their tasks by using different resolutions. As the DPI settings increase, the scan times also get longer. This is because the scanner needs to get and store more data. But the tradeoff here is a richer scanned image. A high DPI setting will allow for a more accurate and faithful copy of the original image.