Limitations to print on the spine of a perfect bind cover
How do I get a grayscale image in a CMYK document?
Don’t forget to check the CMYK values of your grayscale image in the final CMYK document. If there are other values than K in your grayscale image, there is a chance that the color will different.
To eliminate all values other than K, use your Channel Mixer (adjustment layer) in Photoshop, then click “Monochrome” and adjust accordingly. Please see the example below: