Swap Compare To colorspace & control points don't change

(Here’s a question we receive every once in awhile. We’re posting the answer here in the forums so others can learn from this.)

When I change the target color space in Curve2, nothing happens to the output curves. I want to print to the SWOP 3 standard, so I switch the target color space from GRACoL 1 to SWOP 3 - and the recommended control points don’t change at all! How can I know that this software is getting me to SWOP 3 (or any other standard)?

This is a common misperception about Curve2. It helps to start by reminding ourselves about what G7 is and what SWOP 3 or GRACoL are. The former is a method, the latter are specifications.

As IDEAlliance says “G7 is a calibration method for adjusting any CMYK imaging device to simulate the G7 grayscale definition.” This G7 method can be performed on any CMYK printing system. So that includes systems of widely differing inksets, papers (and paper whites). Whatever printer you have, you can run a P2P target through it, measure it, feed it into Curve2 and it will present you with corrections for your RIP to take everything from 0,0 white to 100,100 black, and adjust the RIP curves to be “G7 gray”. All the printers you treat in this way will all be G7 gray and will match each other very well (at least as far as gray balance is concerned.)

Other printers have had this G7 gray done to them. The original GRACoL press runs were done using the G7 graying. But they also had a specific ink defined and specific paper. The SWOP 3 press runs were also done using G7. This has a completely different paper white definition, but it still used the G7 method of achieving gray balance.

So, if you want to print to the SWOP 3 specification, you should probably start by making sure your paper matches the spec. for SWOP3 - and your inks do the same. You can even drop some preliminary measurements into the Verify section of Curve2 to see how closely your ink and paper match the spec. But it’s largely up to your ink and paper choices as to whether your output will line up with SWOP 3 or not. The target space spider graph in the analyze tab is a good place to look to see how closely you come to that. Those bullseye circles which show where you’re aiming toward represent 100% color percentages. When you think about it, if your 100% cyan patch does not hit the cyan circle on the spider graph, there is no way any amount of curve point adjustment between 0 - 99% is going to get you there if 100% can’t get you there.

To avoid some of this confusion we are adding a little reminder in the next version of Curve that the “Compare to” spider graph does not affect calibration.