NOTE: This document details black and white image prep for Blurb BookSmart®. 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-color process is the potential for the introduction of a color cast. There is an accepted amount of color 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-color image, but a color 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 color cast in your images prior to importing to Blurb BookSmart. Here’s how:
All images must be sRGB for BookSmart submission. If your images are already in sRGB, you are ready to go.
BookSmart does not accept CMYK images but it accepts RGB or grayscale images with sRGB being the preferred color space. When importing into BookSmart 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 color cast to black and white images.Figure 1. Check Document Profile
If you use Adobe RGB, ProPhoto RGB, or some other RGB color space, you can use Adobe Photoshop to convert your images to sRGB before importing them into BookSmart. Photoshop is a fully color managed application and can convert your images with a minimal amount of color shift. Make sure to always work on a copy of your image and preserve your original in its original color space.
There are several strategies to convert color 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 desaturate option can be used although it’s not recommended due to its lack of control. Do not simply change the image mode to Grayscale. Since the book is still printed using four colors (CMYK) the grayscale mode will neither be honored nor produce the best results.
A common issue with color 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 midtone range of you 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 eyedroppers (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 all 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 desaturate command. Colors that share the same lightness value but have vastly different hues will convert to the same grayscale value. This means that you will often lose contrast between colors 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 color from your image guarantees that there is no color cast present in your images. However, some photographers prefer to have a slight warm (reddish) or cold (bluish) color 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 color tone than a true neutral black and white print. There are several strategies to add a color 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 BookSmart.
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 BookSmart with Photoshop. The Blurb ICC Profile is available in the Color Management Resource Center.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 checked.
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