Pixel density is a calculation that relates the number of pixels on a device to its physical dimensions, usually in inches. The device in question can range from a large-screened computer monitor or television screen to the smaller screens in your camera or smartphone. Only one number is required, since pixels are generally square, which means the horizontal and vertical density are the same.
While it becomes increasingly important as the resolution of screens has increased, pixel density are not the same as resolution. Where pixel density describes the amount of detail on a physical surface or device, resolution describes how many pixels the device records or displays regardless of its scale.
Pixel density for capture devices that use transmitted light is normally expressed in pixels per inch (ppi). Most digital output devices express their resolution in dots per inch (dpi) although in general, the physical size of the output medium in inches is directly related to the ppi.
Sensor pixel density
Camera manufacturers use the pixel counts of their image sensors
