Wide Gamut Printing with CMYK Inks
Sheet-fed print quality has improved over the last decade for many reasons. Not only has equipment improved, but standards and specifications have provided printers with tools to improve quality. Print specifications and standards such as GRACoL and ISO are designed to provide quality printing results that are sustainable in production through the use of best practices. Simply moving to a print specification such as GRACoL often increases the gamut for ‘uncalibrated’ printers through proper ink targeting. When I asked Marc Levine, for this thoughts on expanded gamut CMYK printing he said,“Before asking yourself if you can beat the standard, a better question is: Can I achieve the standard in a consistent, low cost manner?” This is an important question because more printers are looking for a way to gain an edge over their competitors. In many cases just printing to a specification or standard would improve their quality and increase gamut. Expanding the gamut of your printing process may seem like a low cost way to offer more color, but is it?
Methods to Expand CMYK Colorspaces
The conventional wisdom is that by increasing density you can increase the gamut of the printing press. Many pressmen run to low numbers, especially if they have not calibrated to ISO ink specifications. To expand the gamut, we need to run even higher and this can mean running inks up to 1.70 or 1.80 density, or even higher. There is a limit because at a certain point the ink becomes dirty and color actually degrades. The trick is to push the ink as much as possible, but to back off as the ink dirties. Doesn’t sound too difficult? If you understand LAB and your ink set then this part sounds easy, although it is more complicated than it sounds. Bruce Bayne, developer of SpotOn! comments, “Actually the printing process is only designed to use a certain amount of ink film thickness (IFT). Too much and you have a soupy mess with ink out of control. Inks are designed to print at a specific density with an IFT between 4 and 6 mils. The only way to effectively push ink to higher densities and still maintain balance on press is to mix the ink with a higher pigment load. In the lab they mix ink to have a higher density at the same IFT by adding more pigment to the same amount of ink vehicle (the liquid part, usually soy-based today). Printing at high pigment loads with some inks can cause severe hooking and shrinking of the gamut.”
So it is clear not every ink can handle this extra density correctly. Once you have located appropriate ink and increased the gamut of your press, what do you do next? One generally accepted answer might be to curve the press, but doing this can reduce the gamut of the press, hence reducing the benefit. A reduction curve can be helpful, but curving to traditional CMYK colors can take you right back to normal CMYK. Instead we want to take the high density data and characterize and benchmark the press condition. This requires measuring and creating a target characterization set, and verifying that the data is accurate.
After you have created your target characterization set, workflow considerations kick in. You cannot just throw any file in and expect it to show the benefits of the high gamut target you have created. The key thing to remember here is that traditional CMYK separations aren’t going to get you very far. If you just take a CMYK separation and put it into this expanded colorspace the results are going to be unimpressive. CMYK to CMYK does not lead to great results and in the world of color management it is often considered a bad thing to convert between the same colorspace. This color conversion is very important, and involves using software capable of performing the transform. It can be as simple as converting the images in Photoshop, however this will not help with other elements on the pages. Most often these conversions will be done with advanced software that uses device links. With tools like Alwan CMYK Optimizer, CGS PressMatcher, GMG Colorserver, and FineEye you can improve the quality of your printer – for special printer situations such as wide gamut printing – as well as optimizing your daily CMYK printing. It is very important to have some tools to help make these conversions.
To do this conversion we may choose to come from a wide gamut space such as Adobe RGB and convert to our new target space. While this will improve the look of our sheet, for some customers this improvement may not be enough. Regarding wide gamut color spaces Bruce Bayne states,“Actually the vast majority of images fall pretty close to the GRACoL color space unless they have extremely highly saturated colors. So RGB to CMYK conversion, even to the extended color space will not result in exceptionally brilliant color. Remember the goal of iCC color management is to try and faithfully reproduce the original in a different color space. A normal image then doesn’t instantly become full of brilliant colors.” Because of this we may want to custom separate, correct, and proof images into our colorspace. To summarize – printing to an expanded gamut on your press requires several things. Not only must the press be able to print to higher densities – but also the files require special preparation to really take advantage of this new press condition. If the resulting new colorspace is not dramatically different from a space such as GRACoL is all this extra work really worth it?
Some Advice for the Uninitiated
Elie Khoury, of Alwan Color is a print expert who has implemented wide gamut color reproduction to take advantage of expanded gamuts on conventional as well as waterless offset presses. Elie states, “While high gamut printing is possible especially with dynamic Color Management technologies upfront like Alwan CMYK Optimizer handling the necessary color transformations, clients need to weigh the costs because it is technically more difficult to achieve and stabilize in production and much more expensive to produce than what is usually expected.” Elie suggests to keep in mind that the following is needed for a successful expansion of print gamut in production:
- Specific paper: To avoid ink repulsion at high densities and to have an adequate surface properties (roughness, surface energy…)
- Specific ink: With adapted tack and viscoelastic properties, together with a short drying time (fast oxido-polymerization for sheetfed inks and fast setting (infiltration) for coldset inks)
- Minimum ink and total area coverage: You can achieve that for example with alwan’s dynamic TAC (minimizes TAC for dark areas) and dynamic black/ink savings (output CMY minimized for the output process)
- Press characterization and good averaged ICC profile from various printing conditions
- Top press minders and/or closed loop systems in order to maintain ink film during the print run.
The important thing to remember is that no matter what system is being used to separate the files, printing at high densities is not simply a matter of turning up the densities. There are many other mechanical and technical aspects of the process that make it not just ‘normal’ printing when you are out in the pressroom.
What about ink? Can high gamut ink help the process? There are a number of high gamut CMYK inks available but they typically cost more, and just like traditional inks they have their limits. For most users the goal would be to use their traditional CMYK inks, and turn them up when printing expanded gamut job. Once the job is complete they simply return to their standard settings. As many users have noticed, just moving ink density up does increase the gamut some and makes the sheet look more vibrant.
The real question is can you beat a standard? Is it possible to increase your colorspace beyond the standard and print that way day after day? Are the results appreciatively better than the results of printing to GRACoL or ISO? “The standards are pretty good and are there for a reason”, says Dave Hunter of Pilot Marketing. “I would recommend focusing on improving print quality by printing to and optimizing your print characteristics to the standard.”
The first conclusion is that if you are not already printing to a standard or specification such as GRACoL or ISO you should print to the standard. Before printers invest in the cost of beating a standard they need to invest in achieving a standard. This costs money, but with the resulting improvements it ultimately saves money and improves consistency. This will also likely increase your gamut. If you are already printing to a standard, then the next logical step would be to evaluate and optimize your printing to a standard. Can you achieve the standard on a daily basis? This can be improved with tools for ink optimization, automation, pressroom control, and trending.
The second conclusion is that software alone will not increase your print gamut. ink, paper, and your print technology all play a vital part in your ability to print extended gamut color. These all add to the expense and complexity of printing. Perhaps the most important consideration is the customer requirements. The print buyer is the one who specifies the color to be printed. The key question here is what are your customers demanding? Are they asking for GRACOL/ISO, or are they telling you they want and are willing to pay for the increased costs that expanded gamut printing requires.
What to do if you are interested in trying expanded gamut printing? Contact an expert who has done it before, and despite what some vendors say about easy wide gamut printing – get ready for a rigorous process.
Reproduced with permission from “Printing in the Dark”, Ron Ellis