Digital proofing

“We haven’t had a dot based proof for many years, now,” says Tom Gural, vice-president of Cober Printing in Kitchener, Ont. Instead, this quality printer uses a continuous-tone Veris proofer from Creo (now part of Kodak). “With some customers, we just send them a PDF and they let us worry about the colour,” Gural adds.

Gural’s not alone: since the graphic arts industry began adopting digital technology to produce images and pages, the nature of the proof has been changing, too. In an all-digital workflow, what does a hard-copy colour “proof” really mean? Is there a place anymore for the traditional proof? And if not, what’s replaced it—will the industry accept the fully digital, monitor-based, “soft” proof?

“Certainly, the definition of a contract proof has varied over the years,” says Robert Ens, product manager for proofing systems at Fuji Graphic Systems Canada. At one time, a “contract proof” was meant to resemble as closely as possible the image that the offset press would produce, down to the screens and dot structure. Proofs like 3M’s ColorKey or Agfa’s Pressmatch were made from the same film that was used to make the printing plate, and thus had the same dot structure. Theoretically at least, these proofs would show any moiré or other color problems. Of course, whether they predicted colour that well depended on a number of other factors, such as the substrate or medium that they used and process control. Halftone, “copy-dot” proofs are also quite expensive.

Film proofs lost their niche in the printing ecology when the industry shifted to computer-to-plate processes. In the filmless printing process, proofs have to made from the same digital files as the plate. Today, most customers accept continuous-tone prints as contract proofs; some are starting to accept “soft,” monitor-based proofing systems.

“You can lose a lot of time in the approval process, but the final deadline for printing never seems to change,” says Mike McDonald, President of Ampersand Printing of Guelph, Ont. The company has both offset presses and an HP Indigo digital press. The Indigo can produce its own “proofs” before the final press run, and for offset printed jobs, Ampersand uses a Creo Integris inkjet printer. They also occasionally use colour-calibrated monitor proofs, but “we’ve had a hard time getting people to accept the ‘soft proof’ as a contract proof.” It’s easier to send electronic proofs, but for final approval, especially regarding colour, customers still want to see a hard-copy proof.

The question is: can you make a digital proofing system a reliable predictor of the colour that will result from offset printing?

Digital proofing systems

In a film-based workflow, predicting the product of a printing press can be fairly straightforward, at least in theory. Using the same halftone film to make both the plate and the proof reduces the number of differences between the two imaging processes. Using the same pigments and substrates adds more controls, as well.

Even so, the proofing system still uses a different technology to produce the image than the press does. Only a proofing press can completely replicate offset printing characteristics—and even then, only with careful control.

One common problem is that many customers prefer the look of the proof to the final printed piece. Every printer has had to deal with inexperienced print buyers who want to get the rich colour and high gloss of the Cromalin proof from the offset press.

A digital workflow compounds this problem. There is no film to make the plate, so that one important aspect of controlling the fidelity of the proof is gone. Making sure that the proof is an accurate predictor of the final colour image from the offset press becomes a matter of careful set-up, characterization of every device and process in the workflow, working out translations between the different technologies and constant calibration and checking to ensure that all these devices remain within their specified profile range.

In one sense, it can be argued that if you can calibrate a continuous-tone printer to provide a reliable, realistic proof of offset printed colour, you could do the same with colour on a monitor. There are several vendors who do just that. Still, this route adds another challenge, that of somehow getting a monitor, which displays RGB colour, to emulate printing’s CMYK. And as in hard-copy proofing, to be really reliable, the monitor has to be viewed in the right lighting conditions. The standard for SWOP proofing is 5000 degrees Kelvin.

Digital proofing technologies

The digital workflow necessitates a digital proofing system, one that produces pages, printer’s spreads or signatures directly from the same digital files that will produce plates. Solutions fall into four categories: wide-format inkjet printers for producing signatures, used for verifying pagination and position, but not necessarily colour accuracy; high-quality, continuous-tone inkjet printers for emulating press colour; and monitor-based, “soft” proofing technologies that may or may not be linked to a paper proofing system.

“Printers today will employ a number of different colour proofing technologies at different points in the production process,” says Brad Palmer, General Manager, Proofing and Colour with Kodak Graphic Communications. A high-resolution, continuous-tone proofer may be used as a “final” proof to approve colour, but before that, printers may have customers sign off on the layout using lower-quality, and cheaper, single-page printers; at another stage, they’ll use wide-format printers to check imposition and registration, and to ensure that all the graphic elements are in the final file.

Position proofs

Wide-format inkjet printers have become the norm for producing signature proofs to check imposition. Hewlett-Packard, Epson, Xerox, Encad, MacDermid-Colorspan, Agfa, Canon, Durst Phototechnik, Gerber Scientific Products, Kodak, Mimaki, Mutoh, Nur and more make wide-format colour printers with varying degrees of colour accuracy and control.

Agfa’s Sherpa-m series of wide-format printers combine signature-size format with high-quality colour controls. The Grand Sherpamatic prints both sides of up to 50 inches for a full printer’s flat, with very high precision.

Continuous-tone, inkjet printers

Fast, convenient and relatively inexpensive, continuous tone (contone) inkjet printers can be configured to produce an accurate contract colour proof. However, it won’t match the colours from an offset press unless they’re carefully set up to do so.

That requires several steps: developing an accurate profile, or description of the offset press that the ultimate destination of the print job, as well as profiles of the proofing device and all the colour devices involved in producing the job. Next, you have to match these profiles, in effect, restricting the range of colours, or gamut, that the proofing system produces so that it’s the same as that of the offset press. Then you have to continually measure and calibrate all these devices to ensure their colour output remains within the parameters you need.

Fortunately, there are several standards that simplify this process: International Color Consortium (ICC) profiles that describe colour characteristics of devices in a consistent way from any manufacturer; SWOP (Specification for Web Offset Publications) standards for describing colour output and inks; and Apple’s ColorSync technology for translating colours between different technologies. When shopping for a colour proofing system, make sure it meets at least those three standards.

There’s a wide variety of continuous tone inkjet printers available today, including the MatchPrint Inkjet from Kodak, the PictroProof from Fuji, DuPont’s CromaProXP and the 10000 series from Epson. Xerox’s Phaser printers use solid inks.

In addition to the Veris line of 2-page contone printers, Kodak continues to support the Iris printers it inherited when it acquired Creo, which inherited them from Scitex.

Halftone proofs

For some printers—and for some printing customers—the only acceptable prepress proof remains one that has a halftone dot pattern. For these exacting clients, there are some digital proofing systems that emulate the plate dot for dot. But there’s a high price to be paid for this level of precision, and still, all the devices have to be regularly calibrated for the system to be at all reliable. In addition to the commercial printing market, Kodak’s Digital Approval Halftone color proofing system is also finding success in the packaging world. “It’s seeing a lot of growth in the packaging market,” says Brad Palmer, general manager of proofing and color with Kodak, based in Vancouver.

The Prediction series from Latran is another proofing system that generates halftone images from digital files. It also has found greater acceptance in the packaging industry, with its longer runs and high demands for exacting colour. Fujifilm’s FinalProof system uses its patented thin-layer thermal transfer technology to place true halftone dots onto the receiver sheet for a true, dot-to-dot prediction of an offset press. Aimed at the high-end commercial printer, it has also found a “new life” in the packaging world.

Monitor-based proofing

“Soft” proofing, or using a computer monitor, has been around for a long time. Printers and clients are used to viewing images, pages and spreads on a monitor to check layout, ensure that all the pictures and text boxes are in place and the type is correct. However, we’ve all learned to be wary of trusting the colour from a monitor: it’s a completely different method of producing colour. After all, monitors produce colour in the RGB “colour space”—that is, using red, green and blue as the primary colours, while the press uses yellow, cyan, magenta and black primary colours. There are some colours that the press can produce that the monitor cannot, and a much wider range of colours that the monitor can display that are far outside the press’s gamut.

Still, since the advent of filmless prepress, a number of vendors have brought out technologies that attempt to mimic the press on a computer monitor.

“Contract proofs are many things to many different people,” agrees Brad Palmer of Kodak Graphic Communications. “Continuous-tone prints, even images on a computer monitor can be proofs; each has a different level of risk for the printer. With better profiling and colour management, it’s possible to use monitor-based proofing as contract proofs.”

Kodak’s MatchPrint Virtual “hasn’t had a huge market penetration, yet, but it’s definitely a technology that’s here to stay,” says Palmer. It’s typically used in conjunction with hard copy-based proofs. Its main advantages are speed and convenience—the printer can send the proof to the customer through the Internet, instead of a courier. Delivering proofs across the country is as easy as sending them across town. As a result, virtual proofing is popular with publications.

Other “soft proofing” systems can be found from Agfa, ICS’ Remote Director, Dalim and Helios. Look for ICC-integrated software.

Colour management

Colour management is the term for keeping all the colour devices working within specified ranges and translating colour data between them so the results look the same.

One vendor that provides a comprehensive solution to accomplish all this is QuickCut Ltd. of Australia. Their latest product, QuickCut ICC 2.0, integrates the Adobe Color Engine to manage the transition between RGB and CMYK colour spaces. In addition to allowing printers to use a monitor to provide an accurate colour proof, it manages colour through the whole prepress process. It captures ICC colour profiles from presses, monitors, scanners and printers and aligns them. It even alerts the printer if the ink weight required in an image exceeds the designated press’s limits.

A number of large advertising agencies use QuickCut ICC to prepare colour ad files before sending them to large publication printers, including some in Canada. “The agencies use our product to set their clients’ expectations realistically,” says Dean Benjamin of QuickCut’s North American office. “ICC sets the expectation of what the file will look like as it comes off the press. Most importantly to the printer or publisher, the proof coming from the agency or advertiser takes into account the real press conditions.”

Not only can QuickCut calibrate a continuous-tone print, it can also ensure the monitor displays press-accurate colours — as long as the viewing conditions are right. This means it can be used reliably for long-distance proofing, as a national publisher would need.

GMG’s ColorProof performs similar functions. Other vendors of colour management systems include EFI, Agfa, Fuji, and Dalim with its Dialogue software.

It is possible

Plainly, it is possible to make a monitor-based proofing system that is as accurate a predictor of an offset press as a continuous-tone printer. It requires careful characterization of the press, the monitor and all the other colour devices in between, including the RIP. You need the right lighting around the monitor, too—just like with a hard copy proof. It also requires that you constantly verify that everything is performing within specifications, again, like a hard copy proof.

Soft proofing is catching on more and more in the publication market, where the deadlines weigh more heavily than quality compared to commercial printing. And they’re much cheaper, per proof. “Cost is always an issue to customers,” says Cober Printing’s Tom Gural.