The square shown above is 200 pixels by 200 pixels. To determine a monitor's PPI, measure the width and height, in inches, of the square as displayed on a given monitor. Dividing 200 by the measured width or height gives the monitor's horizontal or vertical PPI, respectively, at the current screen resolution.

Pixels per inch (PPI) or pixel density is a measurement of the resolution of a computer display, related to the size of the display in inches and the total number of pixels in the horizontal and vertical directions. The display resolution of a Digital television or Computer display typically refers to the number of distinct pixels in each dimension that can be displayed A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video Inches redirects here To see the Les Savy Fav album see Inches. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image This measurement is often referred to as dots per inch, though that measurement more accurately refers to the resolution of a computer printer. Dots per inch ( DPI) is a measure of spatial Printing or Video dot density in particular the number of individual dots that can be placed within the span PPI may also be used to describe the resolution of an image scanner or digital camera; in this context, it is synonymous with samples per inch. Historical precedent Scanners can be considered the successors of early telephotography input devices consisting of a rotating drum with a single Photodetector at Digital photography is a form of Photography that utilizes Digital technology to make Digital images of subjects Samples per inch ( SPI) is a measurement of the resolution of an Image scanner, in particular the number of individual samples that are taken in the space

For example, a display that is 11 inches wide by 8. 5 inches high, capable of a maximum 1024 by 768 pixel resolution, can display about 93 PPI in both the horizontal and vertical directions. This figure is determined by dividing width (or height) of the display area in pixels, by width (or height) of the display area in inches. It is possible for a display's horizontal and vertical PPI measurements to be different. The apparent PPI of a monitor depends upon the screen resolution (that is, number of pixels) and the size of the screen in use; a monitor in 800 by 600 mode has a lower PPI than the same monitor at 1024 by 768 mode. The dot pitch of a computer display determines the absolute limit of possible pixel density. Dot pitch (sometimes called line pitch, phosphor pitch or pixel pitch) is a specification for a Computer display, Computer printer

Typical circa-2000 cathode ray tube or LCD computer displays range from 67 to 130 PPI. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The IBM T220/T221 LCD monitors marketed from 2001 to 2005 reached 204 PPI. The IBM T220 and T221 are LCD monitors with a native resolution of 3840×2400 Pixels ( WQUXGA) on a screen with a diagonal The mid-2007 launched Toshiba Portégé G900 Windows Mobile 6 Professional phone came with a 3" WVGA LCD having a "print-quality" pixel density of 313 PPI. Windows Mobile is a compact Operating system combined with a suite of basic applications for Mobile devices based on the Microsoft Win32 ^[1] In January 2008, Kopin Corp. announced a 0. 44" SVGA LCD with an astonishing pixel density of 2272 PPI. Super Video Graphics Array or Ultra Video Graphics Array, almost always abbreviated to Super VGA, Ultra VGA or just SVGA or UVGA is ^[2][3] According to the manufacturer, the LCD was designed to be optically magnified to yield a vivid image and therefore expected to find use in high-resolution eye-wear devices. It has been observed that the unaided human eye can generally not differentiate detail beyond 300 PPI, however this figure depends both on the distance between viewer and image, and their visual acuity. Eye examination Visual acuity (VA is acuteness or clearness of vision, especially form vision which is dependent on the sharpness of the retinal focus within the Modern LCDs having upwards of 300 PPI pixel densities, combined with their evenly lit and interactive display areas may have vastly more appeal to users than the best prints available on paper. Such high pixel density display technologies would enable true WYSIWYG graphics and further, pave the way towards the elusive "paperless office" era. WYSIWYG (ˈwɪziwɪg or /ˈwɪzɪwɪg/ is an Acronym for W hat Y ou S ee I s W hat Y ou G Historical perspective The paperless office was a Publicist 's slogan meant to describe the Office of the future. ^[4] For perspective, such a device at 15" screen size would have to display more than four Full HD screens (or WQUXGA resolution). A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video The QXGA, or Quad eXtended Graphics Array, display standard is a resolution standard in display technology

The pixel density is useful for calibrating a monitor with a printer; software can use the PPI measurement to display a document at "actual size" on the screen.

PPI can also describe the resolution in pixels, of an image to be printed within a specified space. For instance, a 100x100-pixel image that is printed in a 1-inch square could be said to have 100 pixels per inch, regardless of the printer's DPI capability. Used in this way, the measurement is only meaningful when printing an image. Good quality photographs usually require 300 pixels per inch when printed.

Calculation of PPI

Theoretically, PPI can be calculated from knowing diagonal size of screen in inches, aspect ratio and resolution. The aspect ratio of a Shape is the ratio of its longer Dimension to its shorter dimension This can be done in two steps:

1. Use the Pythagorean theorem to determine physical width and height of screen from its diagonal and aspect:

w² + h² = d²

w:h = 4:3

2. In Mathematics, the Pythagorean theorem ( American English) or Pythagoras' theorem ( British English) is a relation in Euclidean geometry Divide width resolution by physical width (or height resolution by physical height) to get PPI.

These steps can be summed up in one short formula:

where

• d is diagonal size in inches (12. 1"),
• r_w is width screen resolution (1024),
• a_w aspect ratio width part (4),
• a_h aspect ratio height part (3).

For example, for a 12. 1" screen with 4:3 aspect ratio, the width is 9. 68" and with a resolution of 1024×768 we get 1024/9. 68 ≈ 105. 79 PPI.

Note that these calculations are not very precise. Frequently, screens advertised as "X inch screen" can have their real physical dimensions of viewable area differ, for example:

• HP LP2065 20" monitor — 20. 1" viewable area[1]

References

See also

• List of Device PPI
• Dots per inch
• Dot pitch

External links

• All About Photo Printing - The Differences between DPI and PPI
• Monitor DPI (or PPI or pixel-density) calculator