DPI vs PPI
To correlate the real world with the digital world, we need to have some units that make it easier for us to determine the equivalent size of the digital image. Dots per inch or DPI is a unit of measurement that we most commonly see. At its basest, it is simple a measure of how many individual dots can be squeezed into an inch. It is used in printing technologies to indicate how high a quality a printer is capable of reproducing. Pixels per inch or PPI is a measurement that is used in displays. You can obtain it by dividing the number of pixels by the length of the display along the same axis. These values are not really fixed as users can change them depending on their needs. DPI can be changed with the printer’s supplied drivers while PPI can be changed simply by changing the display resolution.
DPI is often used instead of PPI in areas where it is inappropriate, simply because people are already used to it. A good example for this is in imaging software where they use DPI to indicate how many pixels should be in an inch. Although this is technically true as a pixel can be considered as a dot, it breaks the convention for the usage of both terms.
The values of DPI and PPI are not equivalent as having the same value for PPI and DPI would often lead to inferior printouts especially in photos. A pixel element on screen is capable of displaying a wider range of colors compared to ink on paper. In order to have the same image quality, the printer needs to fool the eye of the observer by placing multiple dots in close proximity to each other. PPI values for screens often range within a couple hundred while printers can have DPI values of well over a thousand, depending on what kind of printer it is. Obviously, higher values results in a better image quality of the printed image.
1. DPI is a unit used in printing while PPI is a unit used in digital displays and imaging
2. DPI and PPI are not fixed as users can opt for lower values
3. DPI is often used wrongly in place of PPI
4. DPI values have to be much higher than PPI values to achieve similar results on screen and on paper
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