Resolution: DPI and Megapixels

Two terms often used to describe the resolution of an image are dpi (dots per inch) and megapixels. These terms are related, but not synonymous. A slide scanned at 1500 dpi will result in a digital image which is 2168 pixels wide and 1479 pixels high. Multiplying the pixel height by the width gets the megapixel count, in this case 3.2 megapixels. This is similar to the image size produced by today’s consumer digital cameras. A typical monitor or projector has 1024 pixels width and 768 pixels height, resulting in less than one megapixel. A 3.2 megapixel image will need be resized in order to fit the screen. For print, however, higher resolutions are advantageous. An 8”x10” print at 300 dpi requires a digital file 7 megapixels in size or it will appear grainy.