How to Prepare Black and White Images for Blurb BookSmart®

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:

1. Convert your images to the sRGB color space using Adobe® Photoshop®

   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.

   Check that your image is not already sRGB

   • You can do this in Photoshop by clicking on the menu on the bottom left of your image window and selecting Document Profiles as in Figure 1 at right.
   • Remember, if the image is sRGB, you do NOT need to do a conversion.

   To convert the file if it is not sRGB

   
   Figure 2. Convert to Profile
   • Select Edit > Convert to Profile (you may also need to select “Show All Menu Items” if the ”Convert to Profile” item is not available.)
   • Select sRGB as the destination.
   • Select Perceptual as the Intent and Adobe ACE as the Engine to achieve the best possible match between Adobe RGB and sRGB without losing subtle gradations and transitions. Select Black Point Compensation to preserve shadow detail. Select dither if you want to add a small amount of digital noise to break up gradients that are banding. You should always use dither if your image contains large areas of subtle gradations.

2. Remove all color from your image

   
   Figure 3. Black and White Adjustment

   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.

   Using the Black and White Adjustment

   
   Figure 4. Black and White Adjustment
   • Edit > Adjustments > Black and White. This method allows you to tweak the contrast of the image.
   • By adjusting the sliders you will get a real-time preview of your effects and can control how you would prefer colors to translate to a black and white image.

   Increasing Contrast

   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.

   • Image > Adjust > Curves. You can also do this as an adjustment layer.
   
   Figure 5. Increasing Contrast

   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.

   Using the Desaturate Adjustment Instead

   
   Figure 6. Desaturate
   • Edit > Adjustments > Desaturate. Although this is the quickest method, it doesn’t allow for any adjustments and may result in both a loss of contrast and a muddy looking image.

   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.

3. Optional: Add a Color Tone (or Sepia) to Your Image

   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.

   Use a Photo Filter

   • Image > Adjustments > Photo Filter. Select from the presets or choose you own color.

   Adjust the Curves

   If your version of Photoshop does not have the Photo Filter feature, you can accomplish similar effects with the Curve tool.

   • In the Curve window, select either Red, Green, or Blue from the drop-down menu depending on the hue you want. Then grab the middle of the curve and pull up or down to see the sepia effect. Only a slight move is needed to give your image some color!

4. Saving Image Files for BookSmart

   Once you have made all your edits, you are ready to save your files and import them into BookSmart.

   Soft proofing your images for 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

   Saving Files in Photoshop

   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.