Dots per inch (DPI)
Photopedia
18 October 2007 15:39
DPI is a measure of printing resolution; in particular it refers to the number of individual dots of ink a printer can lay down on the print media within a linear one-inch (2.54 cm) space.
Up to a point, which is usually determined by the resolution ability of the human eye, printers with a higher DPI specification produce prints with finer detail and higher acuity. The principal limiting factor is the print head technology used by the printer. A dot matrix printer, for example, applies ink via tiny rods striking an ink ribbon, and has a relatively low resolution, typically in the range of 60 to 90 DPI.
By contrast a modern inkjet printer, which sprays minute droplets of ink though a series of extremely small nozzles, is typically capable of resolutions in the range of 360 DPI to 1440 DPI and above. Most ink jet printers are not restricted to a single resolution but offer a number of different settings dependent on the selected printing mode, which is usually influenced by printer driver settings.
It is important not to confuse DPI with another common measure of resolution, PPI (Pixels per inch), or pixel density. In the context of digital photography PPI can refer to the resolution of a computer monitor display related to the size of the screen area of the monitor in measured in inches and the total number of pixels along horizontal and vertical edges of the display area. It can also be used to describe the resolution of a digital camera, or scanner.