Often when working on book illustrations for self-publishing authors, there will be confusion in regard to the DPI (dots per inch) needed for a picture to look good in print.

The confusion comes because web pictures and most artwork designed for viewing on a computer screen will appear at 72 dpi (or, more rarely, at 96 dpi). It looks good on the screen — at least if you don’t zoom in on the view.

The catch comes if such a picture is used for print. That’s because the printed page needs to have 300 dpi to really look sharp. A reader holding a book may bring it up closer to his face to see the finer details in the picture; but even if he does not, the 72 dpi picture is painfully blurred when printed to a book cover or used as an illustration in a book or magazine.

This is why you can’t take a picture that was designed to be viewed on the Internet at 72 dpi and simply slap it onto a cover or into a book and expect it to look good. The result will be a blurry version of the illustration that will be a great disappointment.

What about just increasing the 72 dpi count to 300? That works — if you reduce the size of the picture accordingly. And that will usually be far too small, unless you need to print something the size of a large postage stamp.

You can resample a picture to increase the dpi from 72 to 300 and keep the image’s original size – but the result is again blurry (and, in fact, that’s basically the same process that happens when the picture is used for a print).

There is software that increases the details in a picture allowing you to boost its size/dpi count. But the details are artificial and computer generated. That means sometimes they look fairly realistic, and other times they look rather weird. And there are presently limits to how effective this process can be. So for most pictures, this doesn’t work well, either.

So what’s the solution?

The only viable solution is to start with a much larger version of the picture you need so the proper details are there in the first place. That means your book cover artist creates a large, detailed illustration for you, or (if you’re using a photograph) the photographer gets a hi-resolution snapshot. Right now this is the only way to do things.

As pictures are cropped and reworked to be used in a book, care must be taken to maintain the dpi count. Once in a while I’ll have a client rework a picture and in the process convert it from 300 dpi to 72 — and that will be disastrous when it then goes to print. When you work with material that will go to print, be careful to keep the dpi consistent. Once the dpi count is lowered, the details are lost for that version of it.

Finally, it should be noted that some low-quality printing is done at lower dpi counts (often 150); examples would be newspaper pictures. And some presses work at 350 or higher dpi. But in general, the 300 dpi is what you’ll want to shoot for with most print illustrations used in books and magazines.

Duncan Long is a freelance book cover illustrator for HarperCollins, PS Publishing, Pocket Books, Solomon Press, Fort Ross, and many other publishers and self-publishing authors. See his cover illustrations at: http://DuncanLong.com/art.html