Proof validation and verification

There are many variables to consider in the area of proofing and, unfortunately, much of it gets forgotten in the busy world of printing. Let’s look at the options and the areas of concern.

The first question when it comes to setting up a proofing device is do we align the proof to the press or the press to the proof? It is easier to align to the press because there is less to change (i.e. plate curves). All you need to do is print the ICC target on the press, measure it and load that ICC profile into the proofing RIP; and, voila, you have a match. But the issue I have with that method is you are proofing to your own island and creating a unique environment for customers to prepare files for.

If we align the press to a specific print specification, such as SWOP 3 or GRACoL, then the job of the designer is much easier. We now have a common target, which is the preferred method.

Evaluating and validating the proof can be done in a few ways. Let’s start with the simplest option. A gray linear blend. Create a CMYK linear blend from white to black in Photoshop and print that to your inkjet device. If you see abrupt transitions or colour bands, you should stop, re-calibrate the device and re-profile. A smooth linear blend is the baseline for accurate colour reproduction. If you pass this test, then validating the proof is your next step.

Here are some of the options for validating your proof starting off with the least expensive.

1. Print a test target in your press and proof. Place both in a proper viewing booth and visually check how close they match. Things to look at are:

a. How close does the inkjet paper match your house stock? A blue white proof will never match a press sheet. Avoid photo papers that are manufactured for photographic reproduction.

b. Blues are typically difficult to match because a press can trap the magenta and cyan differently and produce a purple blue. Play particular attention to blues.

c. Shadow detail, pastels, transitions, flesh-tones are all part of the evaluation.

If you require a good press target, please contact me at angus@colourmanagement.ca and I will send you a target for the evaluation.

2. The second option requires a measurement and doing a comparison to an industry standard or internal target. Most of the proofing RIPS offer a module for this. GMG has ProofControl, EFI has Color Verifier, CGS has Certified Proof, Colorburst offers PrintCertification. KODAK has Certified Process for Color Confirmation and the list goes on.

3. The third option is to purchase a third-party solution, such as SpotOn! or ProofSign. The SpotOn! software is not for beginners, but does offer a slew of information from a small colour bar measurement. ProofSign is easier to use, but does not offer the in-depth reporting that is available with SpotOn!

Verifying that the proof is printing consistently needs to come after the proof has been validated. There are many variables that can cause an inkjet proof to stray from its original calibration. Inkjet printers are made up of mechanical, electrical and chemical components. No two mechanical devices are the same and they are subject to wear and tear and possible failure of the electrical parts.

The ink, a chemical substance, will change its interaction when environmental conditions occur. Ink replacements and paper changes can also influence the stability of the device. Lastly, a well-know problem with inkjet printing is that the nozzles are prone to clogging and this alone can cause dramatic changes in the consistency of the output.

As you can see, verifying your proofs for consistency is essential.

Verifying options come in two forms. Most RIP vendors offer a module for verifying by measuring a colour bar and comparing it to a baseline.

There are also third-party options, such as ProofPass from ColorMetrix. This software is very easy to use and can verify as many printers and setups as you want to load. The idea is to establish tolerances that are acceptable for your production and measure proofs regularly to ensure they are within tolerance. If the proof passes, a label can be attached to the proof adding value and confidence.

When a measurement fails, the options are to double check all the variables: did someone load the wrong media? Is there a nozzle failure, or has the device fallen out of tolerance? If that is the case, a simple re-calibration is all that is needed.

When considering a proofing RIP ensure that the re-calibration option is easy to do. With an inkjet that has a built-in spectro, this process can be automated.

Let’s not forget about the all-important-proof in this process. As inkjet proofing matures so does the ability to verify and validate. Two essential components!