Advice for RBG > CMYK conversion

You will probably have to take a guess that “some form of SWOP” will be the simulation space set at the digital printer…

Not all CMYK profiles are created equal, even within the same colour space. Then there are different rendering intents. There is also the possibility to converting into “any” CMYK space, then assigning a SWOP profile to see how it looks. One can also assign different RGB profiles to the original, changing appearance – and not caring, as it is a means to an end – a better CMYK conversion.

In practice it does not really matter what CMYK space you use for such abstract art, the idea will be to maintain saturation and distinction between the hues. End viewers/users of the printed product will not judge or know or even care what the original RGB looked like – but they will judge the final result. I’m pragmatic, do whatever it takes to get the best final result, your competition will and it does not matter to the client whether you followed best practice or not, they just want the best result possible.

This will often be subjective as to what is considered “better”. Your CMYK conversion at the top, one of many possible CMYK versions below (the lower image actually only uses cyan and magenta):

I would try to convince the designer it's necessary to use two spot colors.

Oops, I see this is on a digital press, well, some digital presses can run spot inks.

I'd need to know what .icc profile the RGB is tagged with and your color settings before making any recommendations.  However, in my experiences, if you start with an Adobe RGB and convert to SWOP Coated v2 CMYK the file will be a close match.  You should proof ( hardcopy print ) the file before going to press.  Screen view may not be accurate.

https://forums.adobe.com/people/Scott+Falkner  wrote So I painted each swatch into a Photoshop file and used its much more robust Convert to Profile feature to convert those swatches to CMYK. I am hoping to preserve as much of the saturation and contrast as possible.

Illustrator uses exactly the same profiles and algorithms for Color Management as Photoshop.

I would not know how the Photoshop conversion would be more robust.

I am afraid that, without having the profile from the printer, that this is what it is.

You can try to change the Intent in the Color Settings to Saturation.

Your conversion is muddied up with blacks. That is not an acceptable result. The rest should not be an issue, but since it involves blending tricks and faint transparencies therte's probably no point in trying to "convert" the colors. Rather it seems more efficient to simply reconstruct them from scratch by defining your own colors in AI. Assuming your system is reasonably color managed, there should be no issue with that at all and you should definitely get much brighter colors. Of course you may also have to actually cut the overlapping regions into separate pieces to be able to mimic the automated result of the blending by tweaking your colors without blending modes.

Mylenium