RGB vs. CMYK Profiles

QUESTION -

I am color calibrating an Epson Stylus Photo R2400 on a new computer. It is connected via USB 2.0. I cannot get it to calibrate as a CMYK printer, which it is. I get an error message about the printer not being a post script printer. The folks at Epson have confirmed that it is not a post script printer. Oddly enough, this printer on a previous computer was calibrated, using this software, as a CMYK printer. How can I get it to calibrate as a CMYK printer?

ANSWER -

The error message you describe occurs when you attempt to send CMYK data to a printer that is not being driven by a RIP. The reason is that while the printer uses CMYK colorants, the data that is sent to the printer is RGB data. The profile should be built using the data type used to drive the printer. In most cases this is RGB data. Again the only exception is when you are using a CMYK RIP, but the error message you are receiving would indicate that this is not the case.

It is possible to send CMYK data to your printer using Photoshop, this may be what you have done in the past. This should not be done as the data actially is converted by PhotoShop from CMYK to RGB, and then from RGB back to CMYK in your print driver. If you attempt to build CMYK profiles for use in a RGB workflow you will achieve bad results.