Please excuse my ignorance, but does the Curve2 software generate the correction curve based on the measured Lab values of the P2P output (after it’s profiled) compared to the reference Lab values? Would I then apply that correction curve to the file after it has been profiled (in the RIP for example)? If so, how would the software know what the CMYK build is (post profile) from which to base those corrections? Or do I not understand the process and/or order of when the target is read and the correction curve is applied?
The basic process for a typical press is this:
- The press is brought into good working order (ink limits are defined, linearization is achieved.)
- A press run is done which contains P2P targets
- The targets are measured and the measurement files are brought into Curve2
- Curve 2 supplies a table of correction values (the “curves”) which will bring the press into alignment with whichever method the user is looking for (G7, TVI, etc.)
- These values are entered into whatever part of the workflow will accept the curves. Usually this is the RIP. A few RIPs do not have this kind of table-based input, but most that are intended for presses do.
- Usually another press run is performed with the curves in place, and a profiling target is included so that a press profile can be made. This profile then defines the behavior of the press as it is calibrated to this standard or method, and can be used in your proofer and such.
So the Curve2 software does make curves based on the Lab (or spectral) measurements of the P2P targets, but this is before anything is profiled. Does that sort of answer your question? There is a more complete description of the process in this article: The Why and How of G7 Calibration
BTW, this process shows why our Virtual Press Run (VPR) module is so valuable. With VPR you can run your P2P target and profiling target - both - on the first press run, and VPR will “curve” your profiling target measurements so you can make that press profile without doing a second run. We even have OneRun targets available so you only have to print a single target on one press run.
Good question. It’s kind of nice to go over the basic workflow like this because I’m sure there are a lot of people who have questions about it.
Thank you Patrick, you answered my question perfectly.
That makes sense because at this stage the CMYK values haven’t been converted yet by a profile. So when Curve2 tells me to make an adjustment, the values match.
We perform calibration (ind. ink restriction/linearization/TAC) before profiling but we hadn’t tried bringing the press into G7 specs at this stage. It sounds like we should. Profilemaker does a pretty good job with grays. But if I’m understanding you correctly, the closer to specification you make a device during calibration, the better the “behavior” for the profile to define.
Thanks again for taking the time to explain this to a dummy.