Editing Pixel density (section)

== Basic principles ==
Since most digital hardware devices use dots or pixels, the size of the media (in inches) and the number of pixels (or dots) are directly related by the 'pixels per inch'. The following formula gives the number of pixels, horizontally or vertically, given the physical size of a format and the ''pixels per inch'' of the output:

:<math>\text{Number of Pixels} = \text{Size in Inches} * \text{PPI}</math>

Pixels per inch (or pixels per centimetre) describes the ''detail'' of an image file when the print size is known. For example, a 100×100 pixel image printed in a 2&nbsp;inch square has a resolution of 50 pixels per inch. Used this way, the measurement is meaningful when printing an image. In many applications, such as Adobe Photoshop, the program is designed so that one creates new images by specifying the output device and PPI (pixels per inch). Thus the output target is often defined upon creating the image.