For most people, the topic of output screening is like those high-school trigonometry courses that made your eyes glaze over. Yet, beyond crunching the numbers to determine where the spots and dots are going to go, output screening actually has relevance to the rest of the package-printing process—especially the bottom line.

Furthermore, the last year or so has seen considerable activity on the part of prepress vendors, and even one prepress house, developing new screening technologies for both offset and flexographic printing. The reasons? Better quality results, more stable processes and, hopefully, reduced operating costs.

Those with a long memory will recall that stochastic—also called frequency modulated, or FM—screening was introduced about a decade ago for use in commercial printing. The idea was that by using extremely fine and precisely located spots, rather than building a halftone dot, printers could produce higher quality printing. The other claimed benefit was that it would facilitate the use of spot colors by eliminating screen-angle conflicts that arise as the number of separations increases.

Alas, the first generation fared poorly, a result of immature technology and, more importantly, a requirement that the press operators change their habits—not a prescription for success. FM screening also performed poorly when printing solids, never a good thing in packaging. Finally, in the event the press went out of register, the operator lacked a rosette "target" to aim for when pulling the press back into register. As a result, virtually everyone stayed tuned in with conventional AM (amplitude modulated) screening.

Well, FM screening is back, with a twist. Leading vendors such as Esko-Graphics, Creo, Agfa and Enovation Graphics (née Fuji) have all come out with screening technologies that combine two algorithms to maximize print quality throughout the tonal range, as well as with solids. Adding to the mix, Cincinnati-based tradeshop Phototype has developed its own technology, called NuDot, for flexo printing on films.

These technologies, called transitional screening, combine different types of screening on different parts of the plate. With the ones used by Agfa, Creo, Enovation and Esko-Graphics, stochastic algorithms are used for the highlight and shadow areas of images, while conventional screens are used for the midtones as well as for solid coverage areas. The reason is that stochastic excels in highlights, but struggles with dot gain in the midtones, while AM screening is best suited to these areas. Combining the two enables package printers to achieve far better image quality than using either one alone. And you can combine more than two: Esko-Graphics' system permits up to 16 screening algorithms to be imaged on the same plate.

The real and perceived benefits of this are great. Printers now have greater control over vignettes and are able to produce very soft transitions across the tonal range. Vendors claim that, by using transitional screening, package printers can run solids, linework and halftone images on the same plates to reduce the number of plates needed for a given job.

Stochastic screening can also increase the gamut achievable with process colors to further reduce the need for spot colors—thus cutting both makeready and press-changeover times. Toward that end, Creo has released Spotless Printing for offset folding cartons, which bundles Staccato FM screening with color-matching software to run a six-color workflow.

Phototype has taken a slightly different approach with NuDot. This technology uses conventional round dots for the highlights, but then shifts to a cross shape with "arrowheads" at the ends of the arms as density increases. As you move through the midtones, it builds a matrix, while solid areas are imaged with a high-frequency screen with openings on the plate to keep ink from "clumping." Phototype claims that one client has been able to increase press speeds by 56 percent—from 525 fpm to 820 fpm, while reducing makeready time.

Although it uses a different approach, Artwork Systems is trying to solve the same problem—achieving good solids. It has adopted the model of the anilox roll to the platemaking process by imaging cells in the solid areas of the plate, while using conventional screening for the halftone areas.

Both Artwork Systems and Phototype claim their technologies produce more uniform coverage with better ink laydown and higher densities, and that they produce better reverse type and significantly reduce halo problems that are common to flexo printing. And Artwork Systems' Mark Samworth says it reduces the volume in the anilox cells by between 10 and 40 percent, and lowers ink consumption by a lesser amount, though he concedes the data is anectdotal.

The bottom line with all these new systems helping package printers and converters deliver a better product to their customers faster and, possibly, reducing operating costs to preserve profit margins. Given the intensity of competition out there, as well as the pricing pressures, those are topics that won't bore anyone in the converting industry.

Alex Hamilton, Consulting Technical Editor, 215/247-3461, info@candcc.com