The material in these guides is recommended for advanced users – such as creative professionals – who require the highest possible precision in rendering color. For most users, an understanding of the advanced concepts of color management is not necessary to produce a great-looking book with Blurb.
For more information, visit our Color Management Resource Center.
NOTE: This document details black and white image prep for Blurb BookWright. For information about image prep for Adobe Indesign or Blurb’s PDF to Book workflow, see How to Prepare Black and White Images for Abobe InDesign and PDF to Book.
The biggest challenge printing black and white images in a four-colour process is the potential for the introduction of a colour cast. There is an accepted amount of colour drift within the world of digital offset presses and this acceptable delta is defined by Hewlett-Packard. Most people would never notice a slight shift in Cyan within a full-colour image, but a colour shift in black and white images is another story.
So what to do? The best thing you can do is to be sure there is no underlying colour cast in your images prior to importing to Blurb BookWright. Here’s how:
All images must be sRGB for BookWright submission. If your images are already in sRGB, you are ready to go.
BookWright does not accept CMYK images but it accepts RGB or greyscale images with sRGB being the preferred colour space. When importing into BookWright all other RGB images are converted to sRGB. However, this automatic conversion from RGB to sRGB may not be optimal for your specific images and may introduce an undesired colour cast to black and white images.Figure 1. Check Document Profile
If you use Adobe RGB, ProPhoto RGB, or some other RGB colour space, you can use Adobe Photoshop to convert your images to sRGB before importing them into BookWright. Photoshop is a fully colour-managed application and can convert your images with a minimal amount of colour shift. Make sure to always work on a copy of your image and preserve your original in its original colour space.
There are several strategies to convert colour images to black and white using an imaging tool such as Adobe Photoshop. We recommend using the Black and White function – available in newer versions of Photoshop. The de-saturate option can be used although it’s not recommended due to its lack of control. Do not simply change the image mode to Greyscale. Since the book is still printed using four colours (CMYK) the greyscale mode will neither be honoured nor produce the best results.
A common issue with colour to black and white conversion is a loss of contrast. You can add contrast to your image by applying a slight s-curve to your images.
By using an s-shaped curve, you can improve contrast by darkening the shadows and lightening the highlights.
You can use this same technique to lighten up dark areas overall or to improve the mid-tone range of your images if they are too dark. Just grab the curve either in the middle or slightly to the left of middle and pull up.
You can also use the eye-droppers (circled in screenshot) to select your highlight and shadow areas of your image for better contrast control.
In the Info palette, individual RGB numbers should now all be equal (in the example shown in Figure 6 they all read 68), which means that your file is digitally neutral. However, you may notice that the image is flat or muddy. This is due to the nature of the de-saturate command. Colours that share the same lightness value but have vastly different hues will convert to the same greyscale value. This means that you will often lose contrast between colours leading to a flat image. Newer versions of Photoshop have a Black and White adjustment that we recommend using for more control and better results.
Removing all colour from your image guarantees that there is no colour cast present in your images. However, some photographers prefer to have a slight warm (reddish) or cold (bluish) colour cast to match a traditional feel of black and white paper or sepia tone process. There is a benefit in adding a tone, as it can be easier to hold a colour tone than a true neutral black and white print. There are several strategies to add a colour tone to your image. We explore two of them below.
If your version of Photoshop does not have the Photo Filter feature, you can accomplish similar effects with the Curve tool.
Once you have made all your edits, you are ready to save your files and import them into BookWright.
You can soft-proof your sRGB files using our Blurb ICC Profile to get an idea of how the images will look when printed. See our documentation regarding Soft-Proofing for BookWright with Photoshop. The Blurb ICC Profile is available in the Colour Management Resource Centre.Figure 7. Saving a Copy
We recommend that you save a copy of your Photoshop files that have been converted to sRGB and keep your originals as they are. The sRGB files should be saved as jpegs with Embed Profile ticked.
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