Cients sometimes have a grayscale image in an otherwise full-color job. They know the grayscale image would look better if reproduced in CMYK, but don’t know how to make that happen. Simply changing the color mode in Photoshop from Grayscale to CMYK doesn’t help. Is there a smarter way that improves the image?
Yes. And, you’re right: When printed in a CMYK publication, grayscale photos can look much better if you create the gray from all four CMYK inks. The result can have a much wider tonal range than a simple grayscale image because it can use all four inks to make halftone dots. But some curves need to be applied to the separate inks to bring out the details in the image and optionally to impart a warm or cool effect.
The easiest way to convert a grayscale image into a successful quadtone is to use Adobe’s presets. In Photoshop, choose Mode> Duotone. Then choose Quadtone and click the Load button. Navigate to the Photoshop application folder, and within it go to: Presets/Duotone/Quadtone/Process Quadtones. Then choose among the presets: CMYK cool, very cool, neutral, warm, very warm, or ext warm.
Thanks to Mike Dinsio and Hopkins Printing for this reminder. You can find more helpful tricks on the Photoshop help site.