Why not CMYK for color separations?
Although many gum printers believe that a simple conversion in Photoshop to CMYK gives you a straightforward conversion from RGB to CMY plus added black for extra density, this is simply not the case. Many teachers and printed sources (James, for example) have compounded this misconception by recommending this seemingly simple route to color separations. It’s true that if there were a way to get a CMYK file with all the settings turned off, then the separations generated from a CMYK file should be exactly the same as the separations generated from the RGB file. However, the whole purpose of CMYK is to change the color values to accommodate the requirements and limitations of printing inks, papers and presses or other printing devices, and the default CMYK space is no exception. Note: My comments on this page refer only to this default CMYK space in Photoshop, and not to any other CMYK spaces or profiles that gum printers may have developed or adapted for their own use. There are people
