Whether you want to print a collection of portraits, an album of photo memories or a collection of artistic photography, the rendering of images is a central issue in the process of publishing your book.

At Rapido, we favor the printing of black and white books enriched in a four-color process. This method produces deeper blacks and richer shades of gray. This process was used to print the book The Extra Mile, by Pierre Gauthier.

In order to avoid different renderings on each page of your work, which would be completely unsightly, it is essential that the processing of all your images is homogeneous in your print files. Without claiming that our recipe is universal, we have gathered in this article technical explanations, validated by two of our collaborators who are experts in Adobe solutions, which will allow you to start on the right path.

Technical prerequisites

Before going any further, you must first remember that the work of the photographer takes place in an RGB flow while the printer works with presses that use a four-color process, or CMYK. You will therefore have to convert your black and white images to CMYK in order to obtain a “soft proofing” screen simulation that is as close as possible to the final rendering in CMYK (For more information, see our article: Colour reproduction).

We then recommend that you do one or more test prints on your own printer. This will be the best way for you to establish a production process that is in line with our industrial presses. In the case of the book The Extra Mile by Pierre Gauthier, this required several back and forths, but it is what allowed us to obtain the result desired by the artist.

Choice of method

To do this conversion to CMYK, you’ll use what’s called a “GCR” (Grey Component Replacement) or “Gray Balance Stabilization” processing (not to be confused with UCR [undercolor removal]). . This process will allow you to modify the gray balance by adding black to it, which will have two joint effects: avoiding drifts towards an unwanted color cast and unblocking the shadow areas a little.

The late Félix Brünner had developed a whole theory on the subject and convinced his clients, the advertising agencies, to use this technique to produce images that were easier to reproduce on any medium. Be careful, this solution is not a miracle recipe. It is particularly well suited to neutral images or B&W photos which are reproduced in four-color process. It is not useful for very colorful and high-contrast images.

This process also makes it possible to stabilize the images during reprints, that is to say, to limit the differences in shades on the presses when the temperature or the humidity rate varies and that it affects the transfer of the ink on the paper, these deviations particularly affecting the rendering of trichro gray scales (Cyan + Magenta + Yellow). Stabilization is a solution that we also use to produce more neutral solids (ben days) (To find out more, see our article: Colour reproduction).

Applying a GCR profile

To obtain a GCR (Grey Component Replacement), you will need to create a custom CMYK conversion profile in Adobe Photoshop. How to do this? Just go to the Edit menu, choose Convert to profile…, then select the Custom CMYK option:

Click on OK

A new window will open, in which you will apply the following recipe:

Ink Options
– Ink Colors:
uncoated paper SWOP (Uncoated)

Separation Options
– Separation Type:
GCR
– Black Generation: Heavy
– Black Ink limit: 97%
– Total Ink limit: 300% (default)*

*For coated paper, it is possible to go up to 350%, but this risks losing detail. By getting too close to the limit, you risk losing detail in the three-quarter tones (values above 75%), which is never desirable.

After applying the CMYK conversion (with custom GCR profile), you will find that the Cyan channel is often slightly more accentuated than the Magenta and Yellow channels. This slight increase in Cyan results in more neutral grays.
It is also possible to save this profile and quickly apply it to all the black and white images that you will convert to CMYK.

As you can see, it’s not that complicated when you know the method!

Duotone coloring from a file with GCR profile

If you later want to give a tint to your black and white images (a sepia coloring, for example), you can do this by modifying the curves of the Cyan, Magenta and/or Yellow channels. The curves panel is located under Edit, Curves:

However, it would be much better to apply your coloring through a curves adjustment layer. You will be able to name your new layer and keep your recipe to come back to it later in case of modifications:
You are free to make the adjustments you like to add a tint to your black and white photos!

Conclusion

At Rapido, we believe that the role of a printer is more than just pressing ink on sheets of paper and binding them together. The evolution of technologies should not make us forget the spirit in which the master printers have always worked since the appearance of our time-proven discipline: the constant search for quality and attention to detail at each stage of the production process.

For this reason, we regularly publish practical articles on our blog to share with you best practices in the world of publishing and to help you with your printing project.

How to build a layout template
for a book
Choosing the right paper
for your book