DPI, PPI, IPI

By , June 25, 2014 11:31 am

IPI = Idiots Per Inch.

I continue to be amazed and discouraged that after more than two decades of modern image editing, photo editors and graphic designers still insist on describing images using the term “DPI.” It stands for Dots Per Inch, and it’s kissing cousin is PPI, or Pixels Per Inch, and I am here to tell editors once and for all: DPI and PPI don’t describe image resolution.

The reason this is so discouraging is that imaging professionals should know better. The only number that actually describes digital image resolution usefully is the number of total pixels.

I had an editor ask for a “300 DPI” image just last week. Without any other parameters, a “300 DPI” image could be the size of a postage stamp (1 inch by 1 inch at 300 DPI) or the size of a garage door (270 inches by 180 inches at 300 DPI).

If there’s good news in this miasma of ignorance, it’s that you can easily make a change in the “Image Size” dialog in programs like Photoshop to fool editors into thinking there are getting what they want by simply unchecking the “Resample Image” box and entering “300” in the “Resolution” field. Of course, it doesn’t change the number of pixels in the image, but it satisfies the recipient. They could do it themselves, too, but that may be asking too much.

I’m going to make a point to send this to any and all editors who specify they want a “300 DPI” image.

Behold: same file, same number of pixels, but one says 72 DPI, and other says 300 DPI.

Behold: same file, same number of pixels, but one says 72 DPI, and other says 300 DPI.

One Response to “DPI, PPI, IPI”

  1. Wil C. Fry says:

    Oh, joy.

    I tried to have this conversation with [person who once again works at my old newspaper] and she just couldn’t get it. I realize math wasn’t her strong suit, but I’d think anyone who graduated grade school could understand that a thousand pixels is a thousand pixels, no matter how many inches you cram it into.

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