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72 dpi? 300 dpi? An attempt to explain. No

Who has to do with images comes, sooner or later about dpi values. Now it has become engraved in the minds of the time, that should the graphics for the Internet use in 72 dpi and present dpi for printing with at least 300. The latter is entirely correct - but the thing with the 72 dpi is not correct and can be attributed to a lack of understanding of the dpi back.

Today, then an attempt to explain what it has with the dpi, and why they play for the screen (usually) do not matter. I declare aware of my everyday photographic view of things. Too technical, so it will not.

Each digital visual representation is initially present in a fixed pixel size. In a SLR camera with 21.1 megapixels are the example, 5616x3744 pixels, a 10.1 megapixel camera produces images with 3888x2592 pixels. Or the web designer created in Photoshop graphic with a square 300x300 pixels.


A pixel is the smallest possible window size for digital images - small as it gets. If the pixel specification now determines where the actual physical size of a digital image file, for which then the dpi is good? It's simple: For the printing of the file! For bedeudet dpi "dots per inch " - ie dots per inch (= inch).

The pressure is always used a pressure grid. The finer this is resolved, the more valued and the visual impression to the eye. Examples of common pressure grid (source: Wikipedia ):

• daily: 150 dpi
• photo-digital lighting: 300 dpi
• Inkjet Printers: Are Looking at a daily newspaper with a magnifying glass: 1200 dpi

extent also easily understandable the pressure points clearly visible. With an inkjet printing is more difficult.
(But now Never again means that images must be mandatory for inkjet printing at 1200 dpi!)

now again back to our pixel image. The pixels in physical size of the image, we assume for the moment for granted and they can not change. The dpi value is flexible and it does now, how good the pixels are distributed on the printing screen. The consequence:

• the higher the dpi, the smaller and finer the printed image
• the smaller the dpi, the larger and coarser the printed image

As examples of a graphic print with each 72 and 300 dpi now have had them back image sizes:


other words, at 300 dpi, it is possible with a 21.1 megapixel image, a 47.55 print x31, 7 cm in size picture. In the first picture I have changed the measure from centimeters to inches (= inch) to prove that a 300x300 pixel large graphic file for printing at 300 dpi then actually 1 inch in size.

Many figures and examples - but the bottom line is extremely simple:
For display on the screen dpi play no role. Here is the pixel size as the physical image size, the measure of things. First, when an image is printed, come dpi as the "conversion factor" into play and distribute the available pixels on the pressure points of the grid - depending on the dpi of finer or coarser.

Does including thus: One image file can be any size dpi rejected. And even in hindsight - without changing the file itself or its contents somewhat.

the sake of completeness, it should be noted that dpi or point densities play a role not only in print. For this article, but should play no role. Who wants to go deeper - from Wikipedia to .