This article explains how to prepare your black and white images in Photoshop when using our InDesign plug-in or the PDF uploader.
Color casts in black and white images
The biggest challenge in printing black and white images using a four-color press is the potential for a color cast. Most people wouldn't notice a slight color shift in a color image, but a color shift in black and white images is another story.
Getting a totally neutral image can be tricky though, as there's always the chance of a slight color shift. Even Hewlett-Packard, the manufacturer of the industry-standard HP Indigo press, specifies an allowable amount of color shift for their digital presses.
One thing you can do to minimize such shifts is to remove all color from your images, as explained below.
Before you begin
Always duplicate your originals before you begin editing them. That way you can save the originals for other uses.
1. Remove all color from your image
Use the Black and White Adjustment feature in Photoshop
One way to minimize color shifts in black and white images is to remove all color from your image. To do this we recommend using the Black and White Adjustment feature in Photoshop (Image > Adjustments > Black & White). By adjusting the controls, you’ll see a real-time preview of your changes and can control how colors translate to the black and white image.
This feature is only available for images in an RGB color space. If the Black and White adjustments option is greyed, out it's likely because your image isn't in an RGB color space.This means you'll need to work on a RGB version of your image before converting it to CMYK (See the steps at the bottom of this article for that).
What about desaturate or grayscale?
Another option is the Desaturate feature (Adjustments > Desaturate) but we don’t recommend this option due to its lack of control. Images can end up looking flat or muddy.
Nor do we recommend simply changing the image to grayscale, as grayscale won't produce the best results either. Use the Black and White Adjustment feature in Photoshop for the most control over the results.
2. Increase contrast
A common issue when converting a color image to black and white is a loss of contrast. You can add contrast to your image using the Curves tool (Image > Adjustments > Curves). By using an S-shaped curve, you can improve contrast by darkening the shadows and lightening the highlights. You can use Curves to lighten up dark areas overall or to improve the midtone range of you images if they are too dark. Adobe has a tutorial on the Curves tool if you'd like to learn more.
3. Consider adding a tone to your image
Removing all color from your image minimizes the chance of a color shift. However, some people prefer a slight warm (reddish) or cool (bluish) look, or even a sepia tone, in their black and white images. You can achieve this in Photoshop using the steps below.
Another benefit to adding a color tone or sepia tint is that it's often easier for the press to produce a color tone than a truly neutral black and white print. Adding a tone can help nudge your print in that direction and minimize the chance of the color drifting in an unexpected or unwanted direction. There are several strategies to add a color tone to your image, such as using a photo filter or adjusting the curves.
a. Photo Filter
Select Image > Adjustments > Photo Filter, then select from the presets or choose you own color.
b. Adjust the curves
If your version of Photoshop does not have the Photo Filter feature, you can accomplish similar effects with the Curves 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. Convert to CMYK
Blurb’s plug-in for Adobe InDesign and Blurb’s PDF Uploader work best with CMYK images. If your images are already in CMYK and you're done editing them, you're all set. Put your CMYK images directly into InDesign or whatever program you'll use to create your PDF.
If your image is in an RGB color space (including sRGB), then use Adobe Photoshop to convert your images to CMYK following the steps below. Photoshop is a fully color-managed application and can convert your images with a minimal amount of color shift. Once you've converted them, you can place the CMYK image into InDesign or whatever program you'll use to create your PDF.
Use the Convert to Profile feature in Photoshop
- Make sure to always work on a copy of your image and preserve the original, in its original color space, for other uses.
- If you haven't done so already, download and install the Blurb ICC Profile. The ICC profile and step-by-step directions can be found in our article Setting Up a Blurb Color-Managed Workflow.
- Select Edit > Convert to Profile (you may also need to select Show All Menu Items if Convert to Profile is not available.)
- Select Blurb_ICC Profile.icc as the destination.
- Select Perceptual as the Intent and Adobe ACE as the Engine to achieve the best possible match between RGB and CMYK 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.
- Click OK to complete the conversion.
5. Save your files
Once you've converted to CMYK, you're ready to save your files and import them into InDesign or your preferred book layout tool.
- We recommend you save a copy to preserve the original files for other uses.
- Your CMYK files should be saved as JPG, or as a TIFF with Embed Profile checked.
6. Good to know
The 200% test
To check the quality of an image or the exported PDF before you upload it, zoom in to 200%. If anything looks blurry, jagged, pixelated, grainy or "noisy" at 200% then it will look that way (or worse) in print.
Order a proof
It's always a good idea to order and review a single printed "proof" copy of a new book, especially before you order multiple copies, ship it to clients, or make it available for sale. You can read more about ordering a proof copy.