Dots Per Inch (DPI) is a measurement of printer resolution, though it is commonly applied, somewhat inappropriately, to monitors, scanners and even digital cameras.
For printers, the DPI specification indicates the number of dots in each inch that the printer is capable of achieving to form text or graphics on the printed page. The higher this specification, the more refined the text or image will appear. To save ink, a lower concentration is often used for draft copies or routine paperwork. This setting might be 300 or even 150 DPI. High resolution starts at 600 for standard printers, and can far exceed that for color printers designed for turning out digital photography or other high-resolution images.
In the case of monitors, DPI refers to the number of pixels present per inch of display screen. The technically correct term is "PPI" or pixels per inch, but DPI is commonly used instead. A display setting of 1280 x 1024 has 1.3 million pixels on the screen, while a setting of 800 x 600 has 480,000, or less than half the resolution of the higher setting. With fewer pixels, the picture will not have the clarity that can be achieved with a higher saturation. Each dot or pixel reflects a certain color and brightness. The greater the number of pixels, the more detailed the picture can be. More pixels also require more memory, and it can take longer to "paint" images, depending on the system's video card, processor and other components.
Scanners also operate at different resolutions. Scan time will increase with higher DPI settings, as the scanner must collect and store more data. However, the greater requested resolution, the richer the resulting image. A high resolution, or DPI setting mimics the original image in a truer fashion than lower DPI settings are capable of doing. If the image is to be enlarged, a high setting is necessary. Otherwise the enlarged picture will look "blocky" or blurry because the software lacks information to fill in the extra space when the image is enlarged. Instead it "blows up" each pixel to "smear" it over a wider area.
Digital cameras have their own specifications in terms of megapixels and resolution, but DPI is often mentioned in this context as well. Since it in all cases refers to the output image, a digital camera capable of the most basic current standards of resolution —- 3.0 megapixels and better —- will output an image capable of taking advantage of a very high DPI setting on the printer. However, if your printer is only capable of 600 DPI, the extra resolution of the camera will be lost in the printing process. When buying or upgrading components it is therefore critical that each product is capable of supporting the highest standards of any interfacing product.