When Separate RGB/Lab to CMYK Source is turned on, all RGB colors are first converted to the CMYK color space defined by the CMYK/Grayscale Source print option before being converted to the CMYK color space of the printer (as defined by the Output Profile print option). The result is a simulation of the RGB colors that would be output from a printer with the characteristics defined by the CMYK/Grayscale Source profile.

With Separate RGB/Lab to CMYK Source, for example, if a high-quality ICC profile is available for another printer, your printer can simulate the behavior of that other printer.

When Separate RGB/Lab to CMYK Source is turned off, all RGB colors are converted directly to the CMYK color space of the printer (as defined by the Output Profile print option).