Preparing Black & White Photos for Your Book

by Joel Friedlander on March 25, 2010 · 20 comments

Halftone patterns book printing book designOne of the biggest challenges for book printers is reproducing photographs in books that are otherwise mostly text. One of the tasks of a book designer is preparing these photos so they reproduce as well as possible.

Before you can understand what goes into this preparation, you need to know a little about how photographs are reproduced. After all, black & white photos are mostly composed of gray tones, yet we don’t print with gray ink. Translating the gray tones of a photo into an image that can be printed with just black ink, yet still look like a photo, is accomplished by screening the photographs.

Traditionally we used halftone screens, which would produce a dot pattern. Large dots—where the paper is mostly covered with ink—created dark areas of gray, while small, even tiny dots—leaving mostly paper showing—represented the light areas.

If you make the dots small enough, they seems to disappear because the human eye isn’t sensitive enough to see them, producing what looks like a smooth gray tone. You can see this in the two pictures above.

Dots on a Diet

The problem is that the perfect dots produced by the halftone screen, or by software that processes images in the printer’s workflow, don’t always look so perfect when they hit the paper. In the real world, books are printed on fairly soft, porous paper. For fine reproductions of black & white photographs, for a museum catalog, for instance, you would use coated paper, a nonporous paper that keeps the dots of ink closer to their ideal size.

But with the uncoated papers we use in books, the little dots spread out. It’s the job of whoever is preparing your photos for reproduction to communicate with the book printer about how much he can expect the dots to spread, what we refer to as dot gain.

Typically, dot gain in book printing is about 20%. This means that if you have an area in your photograph—like a large expanse of sky—that’s about 30% gray in your original file, by the time the ink and paper come together, the dots can spread to 50% gray. This will affect the midtones—the middle grays—of the photograph the most, and is the reason why black & white photos often look darker and muddier than they should.

There are three principal causes of dot gain:

  1. Ink absorbed into the paper—softer papers will absorb more ink, harder papers will absorb less.
  2. Ink spreading out onto the paper—on coated paper, ink will be squeezed outward creating larger dots. This in turn is affected by the viscosity of the ink used.
  3. “Rimming”—the tendency for halftone dots to be surrounded by a small additional circumference of ink. This is most common in offset printing

The soft, uncoated paper used in books is the biggest cause of poor photo reproduction. It’s just very challenging to get a clear image with a full tonal range on these papers. And many publishers—myself included—prefer the cream or ivory-colored book papers, which are much more restful for reading. But the added color to the paper makes the photos even more challenging, because it darkens the lighter tones of the photos.

Digital Advances

Stochastic screens for book printing of b&w photos

Click to enlarge

In recent years, a different form of screening for printing has been developed, called stochastic screening. Instead of varying the size of the dots, something that could not be done by digital imaging engines, the dot size is reduced, but the printer lays down a greater density of these same-size dots to cover more of the paper, producing a darker tone.


Stochastic screening is based on randomly distributed dots, using a sort of frequency modulation to make a density of dots according to the gray level desired. New advances are creating stochastic screens that combine the frequency modulation of equal sized dots with the amplitude modulation of the different sized dots produced by traditional halftone screening. You can see examples in the accompanying illustration.


By the way, in the illustration you can also see an example of a flat tint, a percentage tint of a color, in this case black. These tints are also produced by screening, but for flat tints the dots are uniform.


These flat tints are also affected by dot gain. If you specify a 60% tone in your layout or art software, you will almost certainly be displeased with the results, when you get your book back and the rich gray you saw on your screen has turned to a muddy dark near-black.

What the Book Designer Does

There are quite a few tasks your book designer or production artist will address when it comes to preparing photos for use in a book. For instance, each photo has to be

  • Rendered in grayscale
  • Scaled and cropped to reproduction size
  • Be adjusted to 300 dpi (dots per inch) at the reproduction size
  • Have levels or curves adjusted for anticipated dot gain
  • Examined for imperfections that can be repaired
  • Sharpened for the intended use

It’s important to leave room in your schedule and your budget to accommodate this work during the production of your book. Nothing is more critical to having the photographs reproduce well. The more important the photographs are to the main theme of your book, the more important it is to prepare them properly.

Takeaway: Preparing black & white photographs for printing in most books is calibrated by the book designer to achieve the best reproduction possible for the given book.

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    { 16 comments… read them below or add one }

    Dimas May 24, 2010 at 12:19 pm

    Hi Joel,

    Just receive a proof from LS. All the pictures inside the book block (BW Book Block on Paperback) is too dark just like what your article said.

    So how do I really ‘levels or curves adjusted for anticipated dot gain’ just as you said.

    Reply

    Joel Friedlander May 25, 2010 at 10:59 am

    Dimas, that’s why we do proofs, to find out how the project will print. I can’t give you a lesson in Photoshop in this comment, but open one of your photos in Photoshop, makes sure the Info palette is visible, and open the Levels dialog. You’ll see three sliders under the histogram that represents the tones in your photo. Just passing your cursor over various places in the photo will show the % of black in the Info palette. You want to move the middle slider to lighten those areas about 15% so an area that now has 60% black should come down to about 45% to account for the darkening that’s happening on press. At least this is a place to start. There may be some tutorials on the many many Photoshop sites that deal with preparing black and white photos for reproduction, and if you find anything you think is really useful, I’d appreciate if you’d point it out here in the comments. Hope this helps, Dimas.

    Reply

    Dimas May 26, 2010 at 9:31 am

    That really helps Joel, thanks a lot for replying.

    I found a couple links regarding turning color photos to black and white (http://digital-photography-school.com/digital-black-and-white and http://www.cambridgeincolour.com/techniques/color-black-white.htm) but they both seems so advance i’ll just try your method.

    Cheers.

    Reply

    Joel Friedlander May 26, 2010 at 10:49 am

    Dimas, there’s a great utility for controlling the conversion from color to b&w (under Image/Adjustments). It gives you a lot of control about how the colors in the original file will be translated into b&w. I assumed your images were already in your file as grayscale, so I suggested the other method which, while not as detailed a tool, is pretty quick once you get used to it. Let me know how it goes.

    Reply

    Andres July 24, 2010 at 1:50 am

    Some more on this context:

    - with uncoated paper usable lpi is between 90-120 lpi, that means pic needs to be 180-240 dpi (check the actual screening with printhouse, if possible)

    - dot gain is also possible to control with Photoshop color profiles:
    go to edit>color profiles and change inks, paper type and dot gain before you starting process pictures (and check with printhouse before, whitch values to use — better printhouses have all needed presets for coated and uncoated papers on their website for clients: for photoshop, indesign, acrobat distiller (at last in europe))

    - use Photoshops View>Proof colors -command thru the tweaking, so you see, whats happening really (if your screen is calibrated)

    - keep original files in reserve; if something goes wrong, you can start ower.

    - keep in mind, that printing routines are changing over time: even how printhouse making plates (chemically or lasercut) can make big difference in real output. So be annoing and call to printhouse every time you preparing a book. Some printhouse people love to tell you all the nitty-gritty and you may loose your fear and get better prints.

    Reply

    Joel Friedlander July 24, 2010 at 8:59 pm

    Great advice, Andres, thanks for that. Especially important to communicate with your printer. With some printers this can be a challenge, but if you keep asking technical questions, I’ve found, eventually you’ll be connected to someone who can answer them.

    Reply

    Marcelo September 24, 2010 at 9:27 am

    I saw a Sebastião Salgado book only w/ bw photos printed with black and gray inks for the midtones. The result is amazing. Do have any idea of how they did it? How they separated the plates?

    Reply

    Joel Friedlander September 24, 2010 at 12:38 pm

    Marcelo,

    Are you familiar with duotones? It’s a process by which you create two printing plates from the same b&w image, each with a different tonal range, then print the two plates with different colors. This can also be done with black/black for richer shadows and a longer tone scale, or with black/brown for a sepia effect, and so on. the black/gray is the usual combination to smooth out the tone transitions and can produce beautiful results. This process has been in use for many years. Thanks for your comment.

    Reply

    Aliyah Marr November 13, 2010 at 12:54 pm

    Another great technique for producing rich B&W effects is to run the photos through a four color process. In other words, a B&W photograph or greyscale flat area would be produced with four colors instead of one. The average viewer doesn’t know that there are four colors, he just sees an incredibly rich photograph.

    I recommend any flat black (other than text) on a color print — bookcover, or color pages on clay-coated stock — be printed as a “rich” black, a percentage of all four colors. Here’s a good percentage to set up in a color swatch in PS:

    C = 40
    M = 60
    Y = 40
    K = 100

    You can alternate the Magenta and the Cyan values, depending on whether you want a cooler or warmer black.

    Reply

    Aliyah Marr November 13, 2010 at 2:20 pm

    I am a graphic designer and I write/design books for creative people.

    I have set up a book of quotations to print on LS, but I have a question about flat gray areas on the inside pages. They tell me they print at 120 LS — I have printed another book with them, and to me the dot is visible and possibly uneven.

    This book’s design is dependent upon the huge 300 pt drop caps on each of its pages. These drop caps are set at 20 percent gray to balance the rest of the quote as black text at 12 pt.

    I am concerned that these gray areas will not look good in print with a 120 LS. So I came up with a way to mimic a stoastic screen effect using fills of bitmaped dithered black dots. The effect is beautiful, but will involve a lot of production.

    I have two potential problems:

    1 – LS tells me that these fills might be read by their machines as continuous tone, and put a half-tone on it, resulting in a moire.

    2 – If my trick works, I am in for a lot of production…

    I have set up my title to run a proof with various fills as a test. I would appreciate any help you can give me. I’d like to not have to go through any more production, but if I must…

    I will keep you apprised of what happens.

    PS I love your blog, and appreciate the information that you share.

    Reply

    Joel Friedlander January 21, 2012 at 11:30 am

    Allyah,

    I’m sorry I missed your question when it was posted, and I’m curious how your test went.

    I wouldn’t advise using that specific design for digital print on demand. If the design is absolutely vital to the message of the book, you should simply switch to short-run offset printing where it won’t be a problem to get the effect you’re looking for.

    You might try dropping the tone to 10-15% and getting a proof without the additional production. I’ve had good success with big type at low percentage screens at Lightning Source.

    Reply

    Lee August 18, 2011 at 2:23 am

    Brilliant and informative site Joel,

    I’m actually looking to print a book with black and white images with a ‘rich black’. In this case say 100%K and 30%C.

    The two printers I wanted to use, won’t really help. While they want their own pre-press to do it of course…

    I’ve never printed beyond grayscale.
    How do I actually go about preparing the images?

    Best thanks to you all,

    L

    Reply

    Joel Friedlander January 21, 2012 at 11:24 am

    Hi Lee,

    Photoshop has many tools to create 2-color photo files, but the procedures are a bit beyond the scope of this article. Try some Photoshop tuturial sites or have a look at Lynda.com

    Reply

    R.D. Stacy January 21, 2012 at 10:58 am

    With the recent demise of film photography and the Eastman Kodak Company, how is this matter handled in the case of digital photographs ? (N.B.: I didn’t read all of the comments, so maybe my query has already been answered.)

    Reply

    Joel Friedlander January 21, 2012 at 11:21 am

    Whether your photo starts off as a print which you then scan to a digital file, or as a digital orignal, it will still need to be prepared to the printere’s specifications.

    Reply

    Andrew July 15, 2012 at 6:39 am

    Joel, great advice. I have been going through this posting with great interest as my book will have approx 160 illustrations, some of them old photographs and maps. I tried your method of adjusting for anticipated dot gain and it seemed to work on the sample (now, 159 more images to go through…). I struggled a bit with finding PoD that would price printing of my book interior at b&w prices but run the printing through color machine to print few pages formated for color illustrations (e.g., old maps). Apparently printer will automatically recognized cymk images and price for color will be driven by these circa 20 pages rather than the rest 300 pages that will be printed as b&w.

    Joel, I wonder if you had experience with such “hybrid” approach? Many thanks for your generosity to share your knowledge with all novices like
    me. I wish that I discovered your blog earlier (we’ll do my next book together!).

    Reply

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