if you must, use for '0' the black, and '250' for white (be real carefull with your sample points) (some printers can't print a 4% dot) this will be good if you want to go straight to your CMYK profile with out further curves. I'm the type of person who says to them selves.. if your corecting for CMYK, use the CMYK method, "show me your curves" if your corecting for RBG use the RGB method " 36, 26, 26, the right figures " BUT I'd advise you not to do both, or do either twice