In the closed loop color control world, there is a lot of hay made of one side of the equation, with little to no attention paid to the other. This is really pretty stupid, but like many stupid things it makes sense. It is ironic that the arguably more important part of the control system never really gets explained, or even mentioned.
Everyone is obsessed with the measurement part of things. Are you using a camera, or a sensor? Densitometry, or spectrophotometry? Are you measuring targets (i.e. a color bar) or not (i.e. markless, or “in the work”)? Opinions abound on the veracity of the methods, the claims made by manufacturers, and the ultimate suitability of each solution.
People miss that the best measurements in the world make for great reports, very happy prepress folks and very little else. Certainly nothing that ships out the door as a finished product. It is the control part of things that actually affects all those skids of goodies the customer is paying for, yet no one is talking about how the control part is done. They just assume that if you can measure it you have the numbers and they’re all you need, right?
As I wrote some time ago, the problem is you are controlling ink keys at the start of an ink train. The ink train is like a bureaucracy – you cannot control it, and you can barely predict it. Imagine figuring out exactly how much your blood pressure will rise while renewing your green card a the INS in Chicago and you have some idea of the difficulty involved. So knowing with great accuracy what your target blood pressure is doesn’t really help you judge how much medicine to take with you to Chicago, does it? The ability to convert a decent measurement into a good ink key move is just as difficult or more so when you consider what adjacent keys are doing. This is where the fancy measurement tire hits the money-making road, and the actual benefit of color control is created.
The reason why these algorithms are not discussed is simple – they’re all software. There’s no cool lighting, or visible machinery to inspect, just software. It’s easier to show someone a stuffed dog than explain an algorithm.
Another reason why algorithms don’t get much mention is that the press OEM may be doing more of the heavy lifting than you think. It makes sense, as the OEM has far better understanding that most of the controls manufacturers out there, certainly on their own presses. But what this means is that the same color control system is mounted on different presses made by different OEMs, you can end up with different performance.
So, if you are shopping for one of these systems, at some point in the process push the prepress folks out of the room and ask about the control side of the product. It might nor might not change your mind but it will add a lot to your understanding of what your buying, which should always be welcome.