Paper tint: The problem with color management and paper simulation

By Ron Ellis

Almost everyone using an inkjet proofer is faced with the problem of paper simulation. Immediately upon calibrating a proofer with any of the high-end RIPs such as EFI Colorproof XF, GMG Colorproof, or ORIS ColorTuner, the customer is faced with a decision of what to do about the paper simulation — the white parts of the proof where the proofing software paints in the paper.

While including a paper simulation may be mathematically more accurate, the appearance often falls short of a proof made on the real paper. And although it seems like just a ‘proofing’ problem, the problem with paper white also extends to the press when we make a proof based on one paper but then run a different paper on press. Some people just live with it, others try to profile every possible paper combination. No matter what we do, the paper simulation we use for proofing and its effects on the pressroom affect all of us.

The official term for the color of the paper is “white point” or “paper white,” and it refers to the color of the paper. It is normally measured in LAB values. Paper white has a great deal to do with the reproduction of the highlight areas of images and also affects process and spot color tints. A good example is when you move on press from a yellow paper to a whiter paper. In this instance a light yellow tint will shift from yellow to green. These subtle changes are something the printing industry has dealt with for years with a shrug. Now that proofing systems are more accurate, customers have come to expect more from the proofing simulations.

 

How to calculate white point

White point on a proof is calculated in one of two ways. The first is to have the proofer paint in the paper tint. In this case, if the proof is on a white stock but the press sheet to be simulated has another color, the proofing system will literally paint the paper white into the proof. If the proof is trimmed down and the paper white simulation is accurate then this can almost appear invisible, but many customers balk at the idea of cutting the proof down. (If people see the white proofing paper bordering the tinted proof they begin to ask questions.) Another method is to turn off the paper white entirely.

This works relatively well if the inkjet paper that you have picked has the same white point as the press sheet you are trying to simulate, but otherwise can cause problems. Many printers will search long and hard for the closest ‘inkjet’ match to their standard press sheet in hopes of eliminating the need for paper tinting. If the inkjet paper is not close to the paper color of the press sheet this can cause problems. The conversation during a proofer installation typically goes like this: “Proof looks good. We have to get rid of that tint in the background.”

“That’s the paper simulation. It is more accurate if we leave it in.”

“Can’t have it.”

The paper tint is turned off in the proof and a new proof is made.

“Paper tint is gone. Color doesn’t look right though.”

“We can turn the paper tint back on.”

“Can’t do that.”

At this point, extensive manual editing begins, and the proof usually never looks as good as the first pull made with the paper tint painted in. The white point editing procedure for most rips can be extensive and time consuming once started. Not all stocks and printers lend themselves to accurate white point reproduction, and on these problem stocks getting an accurate white point can be nearly impossible.

Dot proofers such as the Fuji Finalproof and Kodak Approval, although somewhat rare and expensive, lay the proof down upon the actual paper to be used. (About 85 percent of all proofing is now done on inkjets). These ‘dot’ proofers solve the white point issue because they are using the actual paper. The problem with these proofers is that simply putting the actual paper in does not adjust the dot curves to give the best reproduction on that paper — which is one reason that while these dot proofers make beautiful proofs, they are often less accurate than inkjets.

Without special software, these proofers cannot mix the pigments to match the solids and tones on the press. If the Cyan on the proofer doesn’t match the Cyan on the press, there is no easy way to correct it. So while the paper white is guaranteed on these proofers, it doesn’t mean the color on the proof will be accurate, especially if you are using non-standard inksets.

 

One possible solution

One new option is for dealing with white point on inkjet proofers is produced by a company called The Whole Proof and Nothing But the Proof. They will take a real press stock, wind it on an inkjet roll and coat it with a clear inkjet coating. The paper can then be printed using an inkjet with good results. (The company requires customer buy a certain amount of stock). This new approach has great potential for customers who are using an inkjet but absolutely need to be on the same stock as the press. (This paper can be purchased from colormanagement.com, or directly from TWP.)

With most of the high-end inkjet proofing systems previously mentioned, customers often retain the ‘painted in’ paper simulation to get the full accuracy of the proofing system. When proofing is this accurate, the changes on highlight areas that occur on press when changing (press) paper to a brighter or different stock appear more dramatic compared to the ‘accurate’ proof. This is especially evident and quartertones and other highlight areas. In order to make proofs more accurate in this situation, a customer can either recalibrate their proofer or modify press curves to be custom calibrated to the new white point of this paper. Often times rather than do this — with too many calibrations and curves, management of the proofer and press calibrations can become extremely complicated — the customer will simply change the white point value on the proofer, so that even though it is the same proof, paper and highlight areas will now reflect the changed paper white of the new paper.

While this ‘edited’ or ‘simulated’ paper white is not as accurate as a custom calibration, it will reflect the highlight tints more accurately than the ‘old’ profile. Some photographers will even change this profile white point in their conversion profiles in an attempt to get a better match on images.

 

How to solve the white point dilemma

How do printers and customers solve the whitepoint dilemma? In many cases white point is turned off on the proof. In an equal number of cases, paper white is painted in on the proof. In almost all situations, the printer intuitively understands that highlight areas might not match on press, and thus the printer manages customer expectations as best they see fit. White point can be a frustrating factor in printing and proofing, and as system get more accurate our expectations increase.

 

About the author: Ron Ellis is a prepress consultant who specializes  in workflow training and integration. He worked in the commercial printing industry for 18 years and brings a strong background to all aspects of prepress. He has consulted on numerous CTP installations and he provides color management, integration, training, workflow development, and troubleshooting solutions to the graphic arts community. He can be contacted at 603-498-4553 or through his web site at www.ronellisconsulting.com.