PPI is the acronym from Pixels Per Inch. It is a unit of measure used to quantify the number of pixels found on a square inch surface. To get a clear idea of what it means, imagine a square inch that’s divided and organized in a grid of cells. Each and every cell in that grid has a pixel inside. The number of cells inside the grid, also known as pixels, tells you the PPI. Usually, the Pixels Per Inch value is used to measure the pixel density of displays, such as the monitor you have on your computer or laptop, on your TV screen, and on your smartphone. However, PPI is a term that’s also loosely used for describing the pixel density of scanners, camera screens, or images that are stored digitally. Some people use PPI even for telling you the resolution at which printers print on paper. While PPI refers mostly to screens and digital elements, DPI is a term that’s used correctly when you refer to things like printed paper. The resolution and the quality of a printed paper are rightly measured by the number of ink dots in any given character or drawing. Both DPI and PPI measure similar things, but dots are not pixels, and pixels are not dots, so DPI is not the same as PPI. However, 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). In reality, with a good quality digital photo - 200 PPI will achieve photographic quality in print - so even if they ask for 300 PPI, if you have a photo with 200 PPI it will most likely print just fine as long as it is a good quality. Vector images. You can save you illustrator files as .ai Format. The quality is the as pdf. Actually, as you save the file in Illustrator in the native Illustrator format, Illustrator will include a pdf in the file.
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