<P> Pixels per inch (PPI) or pixels per centimeter (PPCM) are measurements 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 . </P> <P> PPI can also describe the resolution, in pixels, of an image file . A 100 × 100 pixel image printed in a 1 inch square has a resolution of 100 pixels per inch . Used this way, the measurement is meaningful when printing an image . It has become commonplace to refer to PPI as DPI, even though PPI refers to input resolution . Industry standard, good quality photographs usually require 300 pixels per inch, at 100% size, when printed onto coated paper stock, using a printing screen of 150 lines per inch (lpi). This delivers a quality factor of 2, which is optimum . The lowest acceptable quality factor is considered 1.5, which equates to printing a 225 ppi image using a 150 lpi screen onto coated paper . </P>

What is the meaning of ppi pixel density