Why We Have to Do Prep Work on “Print-ready” Files

We are sometimes asked why it takes time to set up “print-ready” cover and interior files for printing. The reason is that print-ready files are rarely actually ready to print. I asked our color department what percentage of files were in fact ready to print when we received them. They estimated that 85 percent needed work! (And that work takes a lot of time–we have six full-time people preparing files for printing.)

The reality is that preparing files for printing books is complex. It’s easy to miss important details—even the most experienced Quark or InDesign whiz needs backup. We’re here to provide that backup. Also, we have to make sure files print properly on our particular digital presses. This is work that all book printers have to do. No easy hitting the print button here! Book binding enforces its own requirements. Such things as the thickness of a particular batch of paper, the characteristics of a particular binding machine, or the tolerances of a book trimming machine mean that digital files must be adjusted carefully so that the transformation from digital file to bound books results in books in an edition our clients are proud to publish.

The things we address in file prep fall under the following categories:

  • Fonts
  • Dimensions and layout
  • Color spaces: RGB vs CMYK
  • Content errors

I’ll run through each of these.


Font issues have actually declined with the near-universal use of PDFs, but they have not disappeared. One issue is technical and has to do specifically with part of the Apple Mac operating system—the Quartz graphics layer. Quartz is what controls how things display on a Mac screen. Quartz incorporates aspects of Adobe’s PDF software. This should mean that PDFs made on a Mac using the OS X Quartz PDF engine should be perfect. However, sometimes fonts don’t print correctly from Quartz-generated PDFs. This is something we look to catch and fix.

Another issue is a very old one: the designer used text styles to generate italics or bolds. These look horrible when printed. We call these fake fonts, because that is what they are. We try to catch them and replace them with the real fonts.

When creating PDFs for printing your book, you should embed fonts to ensure that when the files are sent to the RIP it has the fonts required to create the page image. If they are not embedded when we receive the files, we will see if we have the correct fonts in our library and embed them ourselves. In some cases, we may not have the correct fonts, and we will have to ask you to provide them. In rare cases, we may need to ask you for the InDesign or Quark files used to create the PDF in order to fix some issue that is choking the RIP. We realize that this is a pain, as we then need all the fonts and images that were used in the file, but sometimes this is the only way to make a file print.

Font tips to ensure your book is printed correctly and as fast as possible:

  • Use actual fonts for italics and bolds.
  • When creating a PDF, be sure to embed all fonts.
  • If sending actual InDesign files, be sure to check that all fonts are loaded, all links are updated and then “package” your file, which will collect everything required to print.

Dimensions and Layout

Getting dimensions right is critical. On a paperback cover, the spine has to be printed the right width. If it isn’t, either the edges of the front and back of the cover will impinge on the spine, or the spine will extend into the front and back. The spine width is dependent on the number of pages and the thickness of the paper, which is specified in pages-per-inch (PPI).

The calculation for spine width is:
Spine Width = Pages / PPI + .015625 inches (for binder and glue adjustment)

(Your spine width will be spec’d in the estimate you receive from us and your Customer Service Representative can also send you a template.)

Pretty simple, right? Yes, but translating the decimal result produced by a calculator into fractional inches and setting those in a layout file is error-prone. In addition, while the paper we buy in multi-ton lots has a nominal PPI provided by the mill, the actual PPI varies according to moisture content of the paper and with each batch of paper made. The actual width of the spine depends on all these factors. We make adjustments to ensure everything is correct.

Another layout issue is “bleeds.” If a book has bleeds, that means that the printing runs off the edge of the final trimmed book. Most covers and dust jackets have bleeds; interiors sometimes have bleeds. Bleeds require special handling in printing, because you have to have enough printed area to reliably trim off without unsightly crooked white edges. (Trimming machines typically have tolerances of about +/- 1/16″) We use 1/8″ as our standard bleed, which is a good compromise between having enough safe bleed area and, for printing interiors, keeping printing costs down by maximizing the number of pages we can print on a sheet.

Bleeds are normally necessary for paperback covers and dust jackets. One of the most frequent file issues we see is a PDF that has been created without bleed. In some cases, the designer just hasn’t created a bleed. More commonly, designers will correctly create their document to the precise trimmed dimensions of the cover and extend their images beyond the document boundaries for bleed. However, when they export to PDF they forget to define the bleed area. If you don’t define a bleed area, the image will be cropped at the document boundaries. In either case, we’ll either have to ask you to send us a new file with the bleeds created properly or, alternatively, we are happy to create the bleed ourselves. That can take anywhere from twenty minutes to an hour and a half, depending on how many images are involved.

Some layout software by default also runs crop marks deep into the bleed area. These can show on the final cover (remember the trimmer can only be as precise as +/- 1/16″), and we have to remove them. For interior files, we always remove crop marks anyway to ensure that they don’t show up on the final pages.

While we’re on the subject of trimmer tolerances, the human eye has an incredible ability to detect when two lines are not exactly parallel. It is wise to remember that if you run rectangular graphics or text blocks close to an edge that will be trimmed, you run a high risk of your cover appearing crooked, even if the difference in the margin is only 1/64″ across the width or height of a cover. If you’re not bleeding an element off the edge, keep it at least 1/4″ away. (I know, the designer in you is saying, “What? Sometimes a design would be much better with a nice 1/8″ margin!” I agree, but only in a world where 5,000-lb. three-knife book trimmers have the tolerance of a Rolex.)

Another item is matching the size of the cover to the text. Sometimes the page size of the book changes as the publishing process proceeds. More often than not the cover designer and interior designer are not the same person. Therein lies opportunity for error. It is not a rare event that we get a cover file designed for a 6″ x 9″ book, while the interior file is set up for a 5-1/2″ x 8-1/2″ book, or some other non-matching combo. Sometimes a book is estimated at one trim size, but when we get the files, it is actually laid out at another trim size. In this case we’ll check with you to see what your intent was and which direction we should go with it: 1) scale the file up or down to match the page size originally planned (which will likely result in cropping or adding to an edge of the page), or 2) change the specs to match the page size in the layout files.

Finally, when we print your book we almost always print more than one page per sheet. That way we minimize our paper and printing costs, and can charge you less. This is called imposing the job. Part of the imposition process also involves allowing a little extra paper at the spine: this extra is milled off in the perfect binding machine to provide toothy paper fibers for the glue to attach to, making a stronger bind.

Imposition is not something you should worry about doing: creating the PDF in single pages is the simplest for you and the best for us. If we get a PDF interior file that has been imposed in signatures or set up in spreads we have to undo it, which can be complicated—especially if chapter pages are singles and everything else is a two-page spread. Imposition has to be done every time a new job is set up, and redone every time you make changes to pages. It doesn’t take a huge amount of time, but it does have to be checked to make sure that all the margins are correct, etc. No magic print button in quality book printing!

Layout tips to ensure your book is printed correctly and as fast as possible

  • Double check your book’s specs before sending files to us, including whether the interior and cover file trim sizes match.
  • Whenever a bleed is required–which is always for covers and dust jackets–remember to define a bleed area of at least 1/8″, more if you are including crop marks, when you export to PDF.
  • Adjust crop mark offset to .125″ to avoid crop marks running into final trimmed area.

Color Spaces

We are all used to the beautiful colors we see on our tablets or computer screens, as well as the beautiful colors we see printed on book covers and art book pages. The two ways of generating those colors could not be more dissimilar. Color screens are illuminated from the back, by a consistent light source. Printed paper is illuminated from the front, by whatever is lighting the viewing space — a fluorescent light, incandescents, LEDs, or the sun, all of which vary in the mix of colors (or “color temperature”) of the light they produce. Also, even white paper varies a lot in tint, and the tint of the paper itself shifts the color. Finally, matte and gloss film lamination shifts colors by slightly filtering the light as it passes inward through the lamination, reflects off the printed image underneath, and then passes back out through the lamination layer again.

It goes further.


Computers create color images by making dots combining different proportions of red, green, and blue (aka RGB). In 99.99% of the cases, color book printing presses–either offset or digital–print dots using the 4-color combination of cyan, magenta, yellow, and black (aka CMYK). RGB and CMYK are called color spaces. Both RGB and CMYK work. Both can look great. Both color spaces can produce a pretty large subset of the colors visible to the human eye. The thing is, they are not the same subset. There are colors that you can create in RGB that you can’t create in CMYK, and vice versa.

When you print an RGB image created on a computer on a CMYK press, all those dots made with different proportions of Red-Green-Blue must be converted into dots made with different proportions of Cyan-Magenta-Yellow-Black. That happens either in software like Photoshop or software in a computer called a Raster Image Processor (RIP) that prepares the image for printing on a press. So what does Photoshop or the RIP do with the colors that exist in the RGB color space that don’t exist in the CMYK space? Umm. Throws them away, basically, and substitutes best-guess colors that can be produced in CMYK.

A similar issue exists comparing an image printed on an inkjet printer with the same image printed on a CMYK press. I have an inkjet printer at home I use for photographic prints. It uses nine ink colors, including two blacks. The gamut is ginormous: much bigger than CMYK, and bigger than RGB. You can print colors on these inkjets that you cannot produce on a computer screen and certainly cannot produce on a CMYK press.

Just as white paper is not all the same color white, black on a computer and printed on paper is not the same color black. RGB black is pretty simple: it is a place on the screen where no light is emitted. CMYK black is a place on paper where no light is reflected. The ink colors the area of the paper by subtracting colors from white light as it passes through it and reflects off the white paper underneath. CMYK is therefore called a subtractive process, while RGB is additive, creating colors by emitting different combinations of RGB. In the CMYK process the layer of ink has to be very thin. As a result, an area of 100% black ink or toner often looks weak. The solution is to boost it with 40 percent cyan. In converting from RGB black, best printing practices often dictate that the black areas be converted into “rich black” (black plus cyan) by the software.

In your layout software, you can specify if your black is just black, or rich black, or for that matter “registration” black, which is all four colors. The thing is, on your screen it all looks the same and it is very easy to just use 100 percent black on the screen and not even think about it–it looks perfect! Then when the RGB is converted into CMYK it looks like a dingy dark gray because there isn’t enough oomph in 100 percent black by itself. Registration black can cause too much toner to be laid down and type to fill in. The upshot is we check the blacks in your files and make them work.

Another place where a black can look fine on the screen and poor in print is when black text has been assigned RGB or CMYK colors. After processing by the RIP, the type will be screened and printed in CMYK, which will result in loss of definition of the type. Black type should always be assigned 100 percent black, not an RGB or CMYK color.

Pantone Colors

Pantone colors are a whole other can of brightly colored worms. The Pantone system is a system of mixing and matching printing inks. There are hundreds of Pantone colors, each created by mixing specified proportions of printing inks, in the same way that when you buy paint at a paint store from the little sample chip, the paint store mixes the paint on the spot from a list of foundation colors. Offset printers do the same, mixing up Pantone inks for the job when required. Or they do what we do, which is convert the Pantone color to the best representation possible in the CMYK system and print it on a 4-color CMYK press. Pantone ink pigments, like paint pigments, are created from chemical pigments created synthetically, or from naturally-occurring mineral or biological materials. The whole range of Pantone colors covers a different color gamut than RGB or CMYK. There are colors in the Pantone range that cannot be produced by a combination of cyan, magenta, yellow, and black. As with the RGB to CMYK conversion, the Pantone colors must be converted to be represented in the CMYK system.

A cover file prepared in InDesign or Quark can include elements created in all three color spaces: Pantone, RGB, and CMYK. Ultimately, though, the Pantone and RGB elements are converted to CMYK for printing. It is normally easiest to let the RIP make these conversions. However, sometimes the RIP doesn’t play nice when it converts Pantone and RGB images and color tints. Design effects that involve transparency (dropshadows, glows, transparent colors, beveling) are only handled well in the CMYK color space. So creating a transparency with a Pantone or RGB color or placing a dropshadow or other transparent object over an element that is RGB or Pantone, often results in weird artifacts that can be difficult or impossible to eliminate–even using all the magic at our disposal. Pantone duotones are a special problem: the RIP cannot create a satisfactory duotone without the image being converted in Photoshop to CMYK.

Color Profiles

Our RIPs apply GraCol2006 ICC profile automatically. This profile was designed specifically for use on digital presses, unlike the older SWOP profiles developed for offset presses. Because the GraCol profile is applied in the RIP, you should provide your files without profiles embedded or tagged.

Color: Summing Up

To sum up, different media (film vs. paper, and different shades of paper) in combination with different color creation systems (additive RGB computer screens, subtractive CMYK printers, subtractive 9-color inkjet printers) and different cover coatings (gloss lamination, matte lamination, no lamination) all produce colors in different ways, and each can produce a different, non-congruent, range of colors. All digital color presses used for book printing use the CMYK system. Expecting colors produced on a digital color press to exactly match those viewed on an RGB screen or printed on an inkjet press guarantees disappointment. It can’t happen. Our job is to make our best effort to match colors, and put that best effort on a printed proof for you to review. Unlike offset printing, the proof we send you is printed on the same press that will actually print your cover or dus tjacket. Also—and this is huge—we laminate the proof to show exactly what the colors will look like on the actual covers. It is an excellent way to see what your final cover or dust jacket is going to look like.

For interior files that are to be printed in black and white, we check to see that images are converted to grayscale. Ditto for screen tints: they should be set as a percentage of black rather than RGB or CMYK. RGB and CMYK images print on a black and white printer unpredictably, often resulting in the image printing with flat gray tones instead of a good halftone.

Color tips to ensure your book is printed correctly and as fast as possible

  1. For files that are to be printed in color, create or convert your files to CMYK yourself before you hand them off to us. You’ll get much closer to what is possible to print.
  2. If you want us to match colors, provide a printout, ideally one printed in CMYK. We’ll do our best to match it, though as explained above not all inkjet colors can be matched on a CMYK press. In fact, even CMYK printers will print the same image differently. The best predictor of what your cover is going to look like is printing a proof on the press that will actually print the run and applying any lamination that the final piece will have applied, which is what we do.
  3. Forget about matching a printed image to an RGB image on your computer screen. At best they can only be approximations of each other. You can only compare two print versions with each other, which is why we offer printed proofs made on the presses that will actually print your book.
  4. Place high-res images rather than low-res images. The best rule of thumb is that images should be 300dpi at the size they are to print.They can be higher than 300, but if they are much lower than 300 the images will likely look bitmapped and crude. All line art should be a vector file or, if bitmapped, 600-1200 dpi.
  5. For black and white printing, make sure that images and screen tints are grayscale rather than RGB or CMYK to ensure they print properly.
  6. For type that is supposed to print black, make sure that it is set at 100% black and not any RGB or CMYK color.

Content Errors

Normal practice dictates that the printer is not responsible for errors in the actual text of a book. That’s only reasonable: errors in the text are editorial issues, totally in the control of the publisher. However, we don’t like to see books printed with text errors any more than you do. So we check a number of things that we have seen go wrong over and over again, including:

  • ISBN on cover matches ISBN on copyright pages: ISBNs are just little strings of hard-to-read text that are just begging to be mistyped. The division of labor between the cover designer and the interior designer probably enters into this as well.
  • Author name spelled differently on cover than on title page: This happens more often than you would think! We also sometimes see the title or author name different on the front cover, spine, back cover or title page.
  • Bar code doesn’t scan: This happens because the bar code was sized too small, it is low-resolution, or it was created as a grayscale, which shades the edges of the white spaces between the bars. The white spaces are as important as the black bars in encoding information. In some cases if a barcode is printed in color it cannot be scanned. In each of these cases we will query you for the correct information when we send proofs. Please bear in mind that while we check these things, we do them as a favor to you! Ultimately, you’re the only one who can possibly know when text is correct. If you OK a proof we have to assume you’ve checked carefully and print the run and, of course, bill you.

Content tips to ensure your book is printed correctly and as fast as possible

  • In addition to your normal proofreading process, always double-check the ISBN and author name on the cover with the ISBN on the copyright page and the author name on the title page.
  • Follow size guidelines in putting barcodes on covers.

Thanks to our experts Sarah, Carol, Kelly, Tim, and Paul for helping with this article!