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ppi(1) (Points Per Inch, Pulses Per Inch) The measurement of mouse movement.
(2) (PPI) (Perceptive Pixel Inc.) See PixelSense.
(3) (Pixels Per Inch) The measurement of the resolution of a monitor or scanner. Earlier CRT screens measured around 96 ppi, while LCD screens on laptop and desktop computers today range from about 100 to 140 ppi. In order to display more information, tiny smartphone screens require higher resolution. For example, in 2007, Apple introduced the iPhone with 160 ppi. Three years later, the iPhone 4's Retina Display screen was 326 ppi. The HTC One smartphone came out in 2013 at 468 ppi.
Pixels and Dots
Pixels per inch (ppi) are the number of full pixels per inch on a screen, and each pixel on a color display comprises three or more subpixels, with some exceptions (see PenTile). Dots per inch (dpi) rates printer resolution, and the dots refer to the smallest element that is printed (see dpi).
How Pixels and Dots Relate
A digital image is measured in pixels. For example, a 600x300 pixel image has 600 horizontal pixels and 300 vertical. The way the image appears on screen and paper is determined by the ppi and dpi. On a 100 ppi screen, the image would be 6" by 3". Printed at 300 dpi, the standard for quality printing, the paper image would be 2" by 1". An 8x10" high-quality print would therefore require an image with a minimum resolution of 2400x3000 pixels. To view it end to end on screen, it has to be scaled smaller, because most monitors are not large enough. See dot pitch and RGB.
|High pixel density is why it is easy to read text on smartphones such as these. (Image courtesy of Apple Inc.)|