How can I keep a grayscale image accurate in a CMYK file?

When a grayscale image is converted to CMYK, it may shift in tone once printed — often appearing slightly tinted, such as green or yellow.

To prevent this, review the CMYK breakdown of the image in your final document. If any channel contains values other than black (K), the printed result may vary.

For the most reliable output, remove all color data and ensure the image is built only from the K channel. In Photoshop, using a Channel Mixer adjustment set to “Monochrome” is a helpful way to cleanly convert the image to pure black ink.