The biggest challenge in printing black and white images using a four-color press is the potential for a color cast. There's an acceptable amount of color shift within the world of digital presses, as defined by the press manufacturer Hewlett-Packard. Most people would never notice a slight shift in cyan within a full-color image. However, a color shift in black and white images may be more noticeable.
To minimize any potential color shifts you should make sure there's no underlying color cast in your images before you import them into BookSmart. Here's how.
1. Convert your images to the sRGB color space using Adobe® Photoshop®
All images you place into BookSmart should be sRGB. If your images are already sRGB, you're all set. All other RGB images are converted to sRGB when placing them into BookSmart. However, this automatic conversion from RGB to sRGB may introduce an undesired color cast to black and white images.
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. Make sure to always work on a copy of your image to preserve your original image.
a. Check the color profile of an image in Photoshop
Click on the menu on the bottom left of your image window and select Document Profile. If the image is sRGB, you do NOT need to do a conversion. If the file is not sRGB, convert it now.
b. To convert an image to sRGB
- 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 space.
- 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
To convert color images to black and white we recommend using the Black and White function – available in newer versions of Photoshop via Image > Adjustments > Black & White. Although the desaturate option can be used, it’s not recommended due to its lack of control. Also, do not simply change the image mode to Grayscale.
a. Using the Black and White Adjustment
Edit > Adjustments > Black and White. By adjusting the sliders you'll see a real-time preview of your changes.
b. 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.
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 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 the highlight and shadow areas of your image for better contrast control.
c. Using the Desaturate Adjustment Instead
You can find this option under 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.
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.
Another benefit in adding a tone is that it's 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, such as using a photo filter or adjusting the curves.
a. Use a Photo Filter
Go to Image > Adjustments > Photo Filter. Select from the presets or choose your 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 Curve tool.
- In the Curve window, select either Red, Green, or Blue from the drop-down menu depending on the hue you want.
- 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. Soft proof your image
Once the image has been converted to sRGB you can preview how it will look in print by using the soft-proof option in Photoshop. Soft proofing shows you if adjustments to your image are necessary to compensate for the printing process. For example, soft proofing can reveal if the printed image will lose contrast or if it will be less saturated than expected.
With soft proofing enabled, you can edit your image until you’re happy with the preview, knowing that what you see with soft proofing turned on will approximate what you’ll see in your printed book. (Slight shifts in color and brightness can still occur even with soft proofing. However, soft proofing helps minimize such shifts).
Once you have made all your adjustments, you can save a copy of the image and import it into BookSmart.
a. Enable Soft-Proof in Adobe Photoshop
- Select View > Proof Setup > Custom.
- Select Blurb ICC Profile as the Device to Simulate.
- Select Perceptual as the rendering intent in order to preserve subtle gradients.
- Select Black Point Compensation to preserve shadow details.
- Leave Simulate Paper Color unchecked (recommended).
- Checking the Simulate Paper Color option can result in milky or hazy soft-proof previews if your monitor is too bright (as most are). We recommend leaving this option unchecked.
- If you still want to use the Simulate Paper Color Option then reduce your brightness to a more print-friendly level (between 90-120 cd/m2) when calibrating your monitor. However, this may make your monitor undesirably dim for other uses.
When soft-proof is on your image title bar will indicate “RGB/8/Blurb ICC Profile.” You can toggle the soft-proof on/off by using View > Proof Colors.
5. Save your image files for BookSmart
- We recommend that you save a copy of your image to preserve the originals.
- If your images contain line art, text, blueprints, or scanned content, save them as PNG files. Otherwise JPEG (with Embed Profile checked) is fine.
- Import your images into BookSmart to begin building your book.