Book Illustration and Print-on-Demand Grayscale Photos

One of the biggest sticking points for small publishing companies and self publishers moving to print-on-demand is the quality of the grayscale photos. Reproducing color photos and illustrations is less of an issue because it's rarely cost effective with print on demand, regardless of the quality. It's also important to point out that book illustration doesn't require grey scales if you're clever about it, but photo reproduction does, which complicates reissuing backlist books with POD. In fact, the very worst grayscale reproduction you'll see in print on demand books comes about when the original offset printed book is scanned to create a digital file. Since the original offset printed photos were screened, scanning and reprinting produces interference patterns and horrible resolution.

I'm not going to go into the mechanics of printing grayscales photos in detail, but you should understand that it makes it possible to illustrate books with images that appear to contain a spectrum of tones, despite using only one color of ink or toner, black. The trick is to screen an image, using a physical screen or a computer generated matrix, measured in lines per inch. The more lines per inch, the finer the screen. The relative darkness of the little unit, sometimes called a pixel, is approximated for the human eye by varying the size of the black dot printed in that unit. Only the size of the dot changes, the blackness, whether ink or toner, remains the same. The grayscale image appears to the human eye to contain various shades of grey, but if you look at it through a magnifying glass, you'll find it's just different size black dots. A professional would call the resulting image a bitmap, since it contains only 1/0 data, black or white, and the conversion process is known as halftoning.

When book designers produce books for offset printers, they can optimize the screening of images for the process. It doesn't guarantee great results, the quality of the press operator has something to do with it, but offset printers have plenty of latitude to tweak the printing process for different densities of grayscales, and they are normally printing enough books to make the fine tuning practical. A fine screen doesn't mean the illustration will print better because the screen has to match the process. If the screen is too fine for the process, the ink dots may just spread into each other and make a mess. Print on demand printers don't have that latitude, especially if they are printing one book at a time. The best way to prepare grayscale illustrations for POD printers like Lightning Source is to send them uncompressed TIFF images (keep an eye on the file size, but don't apply a screen) and wait to see the results before you commit to distribution. It may just not be good enough for your needs. Other print on demand printers may have better results, though I'm not sure how constantly, but I wouldn't expect any of them to do as good a job as the 1200 dpi laser printer on your desktop you paid $300 for, especially on a high quality setting. The grayscale photos in many offset printed books don't approach the quality of a good desktop laser either.

The main trick for print on demand book illustration is to avoid grayscale photos and illustrations if at all possible. Never use solid fills (grayscales) for highlighting tables or creating contrast for headers or sidebars. Don't use photographs unless you absolutely have to. Many authors and book designers use photographs out of laziness, they build page count and enhance the aesthetic appeal of the book for browsers, but your print on demand books aren't likely to be stocked on shelves in any case. If you feel that your book requires some illustration, use black and white line drawings. Whether you use vector drawings created by software or just scan hand drawn images and convert them to black and white bitmaps, the result will be fine. I would avoid high densities of black, no solid fill or shadowing, because a toner based process is unlikely to print dark areas evenly. In addition, too many illustrations or too many dark illustrations may cause the laser printer to over-compensate and print the text on the next page too lightly, or blotchy.

So, remember that print on demand is not an exact replacement of offset printing, and try to design your books with an absolute minimum of grayscale photos. Also keep in mind that the level of book illustration today is really overdone, since scanners and digital cameras have made it so easy for authors to send in the kitchen sink, and a straight text book can actually stand out from the crowd. Too many illustrations, especially photos, just come across as filler, as if the author didn't have enough to say but the publisher wanted a fatter book to justify a higher cost.