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The PPI/PPCM of a computer display is related to the size of the display in inches/centimetres and the total number of pixels in the horizontal and vertical directions. This measurement is often referred to as dots per inch , though that measurement more accurately refers to the resolution of a computer printer .
A plan position indicator (PPI) is a type of radar display that represents the radar antenna in the center of the display, with the distance from it and height above ground drawn as concentric circles. As the radar antenna rotates, a radial trace on the PPI sweeps in unison with it about the center point. It is the most common type of radar ...
Various computer display standards or display modes have been used in the history of the personal computer. They are often a combination of aspect ratio (specified as width-to-height ratio), display resolution (specified as the width and height in pixels ), color depth (measured in bits per pixel), and refresh rate (expressed in hertz ).
The constant altitude plan position indicator, better known as CAPPI, is a radar display which gives a horizontal cross-section of data at constant altitude. It has been developed by McGill University in Montreal by the Stormy Weather Group [1] to circumvent some problems with the PPI: Altitude changing with distance to the radar.
The data format is defined by a standard published by the Video Electronics Standards Association (VESA). The EDID data structure includes manufacturer name and serial number, product type, phosphor or filter type (as chromaticity data), timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping ...
If it is labelled as 250 PPI, that is an instruction to the printer to print it at a size of 4 × 4 inches. Changing the PPI to 100 in an image editing program would tell the printer to print it at a size of 10 × 10 inches. However, changing the PPI value would not change the size of the image in pixels which would still be 1,000 × 1,000.
The measure of how closely lines can be resolved in an image is called spatial resolution, and it depends on properties of the system creating the image, not just the pixel resolution in pixels per inch (ppi). For practical purposes the clarity of the image is decided by its spatial resolution, not the number of pixels in an image.
[1] [2] In the case of an RGB color display, the derived unit of pixel pitch is a measure of the size of a triad plus the distance between triads. Dot pitch may be measured in linear units (with smaller numbers meaning higher resolution), usually millimeters (mm), or as a rate, for example, dots per inch (with a larger number meaning higher ...