Pixels per inch (PPI) or pixels per centimeter (PPCM) is a measurement of the pixel density (resolution) of an electronic image device, such as a computer monitor or television display, or image digitizing device such as a camera or image scanner. Horizontal and vertical density are usually the same, as most devices have square pixels, but differ on devices that have non-square pixels.

Calculation of monitor PPI

Display resolution and pixel density.png
Theoretically, PPI can be calculated from knowing the diagonal size of the screen in inches and the resolution in pixels (width and height).
 METADATA-Metadata is "data about data".[1] Two types of metadata exist: structural metadata and descriptive metadata. Structural metadata is data about the containers of data. Descriptive metadata uses individual instances of application data or the data content.

For example, a digital image may include metadata that describe how large the picture is, the color depth, the image resolution, when the image was created, and other data.[3] A text document's metadata may contain information about how long the document is, who the author is, when the document was written, and a short summary of the document.