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 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 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).