Pixels Per Inch
Pixels Per Inch (PPI) is a measurement of pixel density that expresses how many pixels are contained within one linear inch of a display or digital image. It is calculated by dividing the total number of pixels along one dimension by the physical size in inches along that same dimension. Higher PPI values indicate greater pixel density, which generally results in sharper, more detailed visual output when viewed at typical distances.
Display and Imaging Applications
PPI is commonly used as a specification for digital displays, including computer monitors, smartphones, tablets, and televisions. It also applies to digital images and their output resolution when printed or displayed at specific sizes. For example, a smartphone display with 400 PPI will appear sharper than one with 200 PPI when viewed from the same distance, because the individual pixels are smaller and less visually distinct.
Practical Considerations
The perceived quality of a display depends not only on PPI but also on typical viewing distance. A monitor viewed from two feet away may be satisfactory at 96 PPI, while a smartphone held closer to the eye typically benefits from higher PPI values of 300 or above. Print quality also depends on PPI, with standard print reproduction typically requiring 300 PPI or higher for photographs to appear sharp to the human eye.