Convert Black Channel to CMY

Back in the sixties, three color process printing was promoted briefly for short-run jobs and not used in the better printing plants. In the New York area the process was called "Pleasing Color" but it rarely pleased anyone. If you lowered your standards you might say it was adequate in the lighter values and even in some flesh ones... but as the tones extended into the darker values, desired neutrals were almost impossible to maintain. Any shift in ink/water balance on press (affecting dot gain, ink trap and ink density)  produced significant color variation on the run. Pleasing Color went out of fashion very quickly,

If you are thinking of three-color process lithography, I suggest you think again.

The "best way" is to open the file in Photoshop and convert it to the appropriate

CMY colorspace, represented by an ICC-profile which was made for the special

paper, the special ink and the special printing process.

The creation of this profile requires:

a) print a CMYK target onto the paper using exactly the chosen process.*

b) make the profile using instead of common UCR/GCR modes one which contains

no K ink at all (Black Max = 0) :

*) Why one cannot use a CMY target? In my opinion, that's simply not common.

As a result, this profile, that is in fact the printing process, will not show a neutral black.

See green curve (the red curve belongs to a CMYK profile). An the darkest CMY black

is not as dark as CMYK black.

Achieving a good gray balance over the whole lightness scale by manual adjustments

will be very difficult (impossible, IMHO).

Best regards --Gernot Hoffmann