Azara Blog: What is it about dpi that confuses people?

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Date published: 2005/04/06

It is amazing the number of people that email and ask: "Do you have such and such an image available at 300 dpi (for printing)?" (The acronym dpi means dots per inch but for digital photograph purposes this is the same as pixels per inch.) Unfortunately this is a meaningless question, and there is no way to tell someone this politely except by not mentioning the fact at all. What they really want to know is how many pixels you have. All images can be printed at 300 dpi, whether they are 1 megapixel or 24 megapixels or whatever. It's just that the more pixels you have, the larger you can print the image (at a fixed, say 300, dpi). For a 2 megapixel image of size 1600 x 1200, you can print this up to a maximum size of 5.3 x 4 inches (around 13.5 x 10.1 cm) if you want 300 dpi or better resolution (since 1600/300 = 5.3 and 1200/300 = 4). If you are willing to put up with 200 dpi (which in theory looks worse) then for that same image size you can print up to 8 x 6 inches (around 20.3 x 15.2 cm). For most purposes 250, and sometimes even as low as 200, dpi is enough to give a reasonable result (certainly on home inkjet printers), but publishers always seem to stipulate they want 300 dpi, presumably because someone long ago decided that was the figure they wanted and it has stuck ever since without anyone really thinking about it. Far more serious is whether your printer is continous tone or not (which most publishers will have), and another important issue is colour reproduction, since many publishers do not seem capable of doing very well on that front.

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