As much as possible, optimize grayscale images for the black channel only. This makes color control easier and reduces the final production cost. There are various ways to separate a color theme into grayscale, but the matter doesn't end there. Sometimes, separating colors is not that easy.

Imagine you have a full-color image, and a part of it needs to be converted to grayscale. Using the Grayscale color mode will convert the entire file to grayscale, but our main goal is to convert only a part of the file's subjects.

One technique that can create a grayscale area within a CMYK file is using the Gradient Map command. This process can simulate a color subject with the black channel. If you use commands like Hue/Saturation, the image might appear grayscale, but it will be present in all channels, which is very problematic.

Image > Adjustment > Gradient Map

• Use tools like the Lasso or Pen tool to select your subject. Now, run the Gradient Map command and define pure white and black at the first and last steps.
• Your subject will be transferred to the Black channel and become grayscale, while the rest of the file remains colored.

"The Gradient Map tool is invaluable for selectively converting colors to grayscale within a CMYK file, providing precise control over your image's tonal range."