A les­son in Pho­tog­ra­phy often over­looks the famous acronyms of DPI and PPI. Two things that often con­fuse the heck out of peo­ple. Why is it that some images show on your com­puter at 72 DPI when you set your cam­era to the high­est res­o­lu­tion? And How does DPI dif­fer from PPI, I mean, can one let­ter in the acronym really make all that dif­fer­ent? YES. Let’s gan­der at the answer to these ques­tions, shall we?

Let’s start with PPI. Pix­els per Inch. This will affect the print size of your photo and will in turn affect the qual­ity of the out­put. If there are too few pix­els per inch, then the pix­els will be very large and you will get a very pix­i­lated image, thus affect­ing the qual­ity of the out­put. There are 2 ways that you can change the print size, by resam­pling or by not resam­pling. Not resam­pling is what you gen­er­ally want to do; this will only change the size of the print out. Using resam­pling will actu­ally change the num­ber of pix­els (and thus the file size) in order to match the print size.

DPI on the other hand refers only to the printer — Dots per Inch. Every pixel out­put is made up of dif­fer­ent col­ors of ink (gen­er­ally 4 or 6 col­ors — depend­ing on your printer). Due to the small amount of col­ors avail­able, the printer needs to be able to mix these inks to make up all the col­ors of the image. So each pixel of the image is cre­ated by a series of tiny dots. A high DPI printer has more dots mak­ing up each pixel, and thus a higher and bet­ter qual­ity image out­put. Vice versa for a lower qual­ity DPI printer.

Peo­ple often use the terms of DPI and PPI as one com­mon one, which is really not the case. They are both dif­fer­ent, and thus should be used as so.

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