When you’re working on an RGB document in Photoshop, that will eventually be converted to a CMYK document for printing, it’s possible to see both versions at the same time and see the changes you make on the RGB image appear simultaneously on the CMYK image. Follow these steps:
1. Open an RGB image in Photoshop.
2. Choose Window > Arrange > New Window.
This opens another view of your existing document.
3. Press Ctrl+Y (Windows) or Cmd+Y (MAC) to see a CMYK preview of your image.
4. Click on the original RGB image and start editing. Your changes will be updated on the CMYK image as your work.