MORE THAN DOTS AND PIXELS
By Noel Ward

Measuring Quality for Black & White and Spot Color Printing

The disruptive technology of Gutenberg's printing press doubtless had detractors who questioned the quality of the pages the early presses produced. Half a millennium later, print quality is still a primary consideration of anyone involved in the creation and production of printed materials. Then as now, our impressions of quality are influenced by our experiences, expectations and the applications of every print job.

These influences should be balanced with an understanding of several measures that ultimately make up what we broadly describe as "print quality." These range from a variety of technical aspects of how a RIP and print engine conspire to put toner on a page to the extensive engineering of paper and substrates to highly pragmatic measures such as whether MICR characters can be accurately read by an automated reading device.

As printing technology continues to evolve, it is increasingly important to understand these measures, how they influence print quality and they shape our experiences, expectations and the applications of printed documents.

Even with more than 500 years of printing behind us, it is easy to imagine the thoughts of people who saw the first books printed using movable type. Accustomed to books (primarily the Bible) of handcrafted quality which included decorative and visually compelling lettering, the earliest mechanically printed volumes must have been something of a letdown. While some handwork was still possible, most pages were produced using a machine that made them all look alike. While those with vision saw the benefits in terms of saved labor and increased production volume, there were certainly those who saw the first printing presses as unwelcome change agents that sacrificed the elegance and quality of hand-scribed work for the sameness of wooden type pressing ink onto a page. But the disruptive technology of printing presses prevailed and while people today wonder at the devotion required to produce illuminated texts, no one would go back to hand-copying and production of books in the name of quality or efficiency. Quality, though, remains a vital issue, and nowhere in the printing industry is it a greater concern than with digital presses.

What is Quality?
Most people's perceptions—and expectations—of quality are based on the familiar appearance of offset printed materials, especially for books, magazines and a broad range of marketing materials all printed at 1270 dpi or higher. These production documents share higher requirements for print and image quality over transactional documents such as bills, statements and invoices which, for many years, were routinely printed on computer-driven impact devices such as dot matrix and line printers. The limitations of these devices restricted print quality for transactional documents. Even when laser print engines with 240 dpi resolution came to provide the output for most transactional applications the quality was still not deemed sufficient for other types of documents.

Meanwhile, black and white production documents have come to include pages transitioning from offset printing, such as the growing volume of books being produced on digital presses at 600 dpi. These include directories, product manuals, and short-run books, both as new releases and new copies of previously out-of-print volumes. The key shift is the broad acceptance of 600 dpi as a standard print resolution. With virtually all high-speed print engines now delivering 600 dpi even for transactional
documents, the expectations and acceptability of print quality is shifting for both production and transactional pages. Corporate America and consumers alike have decided that the 600 dpi print resolution offered by most LED printers is acceptable for most uses (Figure 1).

Expectations and Quality Expectations
Expectations and levels of quality change depending on application and the environment. However, production printers, data centers and service bureaus—along with their customers are widely agreeing that 600 dpi resolution is sufficient for most needs.

"If you look at the basic hard cover best-seller by John Grisham you'll see somewhat grainy paper, possibly recycled stock, in an off-white shade which makes for easier reading. Someone looking for the highest quality isn't going to be satisfied because the book isn't designed or printed to meet those standards. It's not up to that person's expectations."
—Guy Broadhurst, Océ Printing Systems

How Good is Good Enough?
Understanding and defining the functional and business needs of an application is the first step in determining the print quality required. This is usually the job of a designer or document creator. An annual report for a telecommunications company, for example, probably requires a six-color document with spot colors, varnishes, and high-resolution halftones all lavishly printed on heavy, coated paper. The product manuals for the company's mobile phones, however, are more than adequate if printed four-up on 20-lb. bond on a roll-fed LED printer at 600 dpi, maybe with a four-color cover. Each of these documents matches the quality expectations of both document creators and end users. The annual report projects the corporation's image and face to the world so it has to look the part. The seldom-used and destined-to-be-forgotten phone manual dictates low to moderate production values.

Subjective and Objective Measures
Complicating the issue are the subjective and objective measures of quality. The subjective ones--which can vary from person to person--are what your eyes see and how you react, largely based on experience and expectations. Objective measures such as resolution, grayscale, density, tonality, highlight color, and the paper itself are ones that can be quantified and to some extent controlled. Understanding how subjective and objective measures fit together on a printed page helps determine which print engine is best-suited for a given application--and how to get the best results out of any machine.

For example, an offset printer accustomed to producing documents at resolutions of 1270 dpi or higher may find the limitations of 600 dpi electrophotographic printers almost laughable. It is very important to differentiate between desired and acceptable image quality, explains Walter Young, DemandStream Product Manager at Océ Printing Systems USA. "It's nice to have something that looks like a coffee table book, but there's a trade off in doing that. The higher the image quality, the higher the cost. Higher quality also means more data has to be managed and moved around which requires greater processing speed. There is a trade-off where sometimes the money needs to be spent, and other times when it does not because the document doesn't justify the cost."

Of some applications there is no subjective measure, says Guy Broadhurst, Director of Product Management at Océ Printing Systems. "Take a bar code or the MICR line on a check. The very clear objective measure is whether it will work in a barcode or MICR reader without being rejected. There are ways to measure objective things like toner density, edge sharpness, and dpi because the are all definitive, objective elements." These things are fundamental inputs, along with the subjective ones that determine what is ultimately a subjective measurement (Figure 2).

"Both objective and subjective measures go into defining quality," says Young. "In the end it's how they go together for a specific application and how they can help people understand what they are looking at. It's very important for our customers and their customers to have the information they need to determine if a document meets its quality requirements."

For example, a customer may call for service on their digital printer, thinking the image quality is less than optimal. They just know subjectively that the image isn't "right" but can't articulate what is wrong, except in the most generic terms: 'The pictures are too dark/light, there's too much/too little contrast, the images don't seem very clear.' A service technician may determine that the printer or RIP is not working properly or that the images being used aren't of sufficient quality--all supporting objective measures of quality. Or as sometimes happens, the user is familiar with more offset output and unaware of the differences in digitally printed images. Whichever applies, being able to understand at least some of the objective measures of quality can help identify problems and, more importantly adjust a user's expectations to fit the type of printing device being used.

Educating the Customer
Adjusting expectations begins with education. Printers offering digital printing are finding the best way to do this is by helping customers understand how digital and offset printing differ, their respective advantages and disadvantages, how certain objective measures impact quality, and how these all relate to a customer's applications. Helping customers gain this awareness is vital due to the massive convergence taking place in the market. Several key issues emerge in bringing customers up to speed on the options available for printing. These vary somewhat for transactional and production documents but all are important points when a customer is making the transition from offset to digital or even from one digital press to another.

Managing expectations. Especially for customers familiar with offset printing, it's important to show them the differences between offset and digital output. Part of this education is the differences in the density (darkness) of text and the narrower tonal range available for halftones. When describing these differences it is important to point out other benefits of digital printing such as flexibility, the ability to add variable content, faster workflows, and savings on warehousing and elimination of waste. Equally important is that there can be significant quality differences between print engines of different manufacturers.

Paper. Some of these differences can be lessened by choosing the best paper for a given application. Paper is a very important consideration when shifting a document from offset to digital printing and can make a significant difference in the look and feel of the finished document. Paper weight, brightness, opacity, color, surface characteristics, and thickness (caliper) all have a significant influence on how text and images look on the finished page. While the range of papers available for digital presses was once limited, most paper vendors offer similar choices for both offset and digital printing. This is an important point: the surface characteristics of offset papers (which are optimized for accepting ink) are different than those of digital papers, which have unique requirements for accepting and retaining toner particles. Many paper vendors have engineered papers that will work equally well in both environments.

Consistency (as noted in Figure 2), especially with halftones, is one of the strong points of offset printing. Maintaining halftone consistency is easier on offset press because it is printing the same image every time. Once you get the image printing correctly, you just have to maintain those settings. With digital printing every page can be different and the same optics and electronics used to produce a full page of text at one moment may be producing a full-page photograph the next.

Repeatability (as noted in Figure 2) between different runs is important for jobs that re-run on a recurring basis. For example, a two-color directory of physicians affiliated with an HMO might be offset printed annually in lots of 5,000 copies. Using digital printing this might be done in 8 runs of 625 each, using highlight color. Being able to assure the HMO that the first copies printed in January will look the same as those printed in November is an important quality measure for the keepers of corporate image at the HMO. Both color and halftones are at issue and it is important that a digital print engine have repeatability similar to that of an offset press.

Technical measures are also worth noting so that customers can begin to understand the components of the quality they see on the page. Although most customers will not be interested in some of the details, it is important for them to understand that elements they control, such as the resolution of images included in their jobs have a direct impact on quality.

A Look at Transactional and Production Documents
Consider a utility bill or credit card statement. The ultimate end-user, the consumer receiving a bill in the mail, is unlikely to complain about less than ideal print resolution. Here the information presented is more important than the printing. For simple, black-and-white transactional documents, such as bills and statements, the quality is probably appropriate if all relevant information is conveyed clearly. Since each customer only sees a few pages at a time, consistency may not be an issue, although having every statement or bill look the same over the course of a year is important for a company's image and branding.

Color has long been part of the perception of quality and companies are now adding color to transactional documents. Highlight color is growing in importance as companies look for ways to enhance the look and feel of statements and invoices and in some cases to add eye-catching marketing messages. Most print engine vendors offer a range of highlight colors.

"Run lengths are going down, offset documents are shifting to digital presses, and there are all kinds of price pressures," says Broadhurst. "A certain amount of education can show the printer's customer the advantages that come along with digital equipment." This is indicative of how the acceptable level of quality is changing and being related to the value of a document.

Books, especially in the form of product and service manuals, directories, prospectuses and other bound, multi-page documents have been traditionally printed on offset presses in runs of 5,000 or more. Many of these short-shelf-life volumes are increasingly being printed on digital presses in multiple runs of under 500--with intermittent updates. The costs associated with prepress, production, warehousing and waste of obsolete versions has made digital printing an attractive alternative. The only visual difference is in print resolution, but with 600 dpi being almost universally accepted for such documents, there is little need to incur the added costs of the longer print runs necessary for offset printing. Since these documents are largely black and white with perhaps a spot color, offset printing, despite its higher print resolution, no longer holds an advantage. Spot colors can be quickly added and changed on digital presses. In fact, it is possible for a document that was previously produced on an offset press in black and white and stored for distribution to be produced more economically in two colors on a digital press, with reprints done as needed, adding both visual and economic value to the publication.

Who Decides What is "Good Enough"?
The print quality of digital presses has often been assaulted as not being that of "real" presses--those using offset lithography. While such criticisms were once justified, most digital presses now deliver very good image quality. It may not always look like offset printing. In some cases, the print quality is indistinguishable, in others people prefer the rich blacks of digital printers, and at other times people prefer offset. But, offset isn't always the preference. And printers are adding digital presses to their offerings, replacing offset pages for digital ones for some applications.

Still, quality--a concern of printers long before digital-anything entered their vocabulary--continues to be part of the craft-based heritage of putting images on paper. For the most part, printers have always defined what "quality" was and what was "good enough" for a particular application. This provided a measure of control for print providers who could always point to the quality of their work as a differentiator. But with digital presses turning out both production and transactional pages while removing the craftsmanship from printing, just how high does print quality need to be and who is the judge of that quality?

At the most practical level, the ultimate arbiter of print quality is not the document creator, designer or printer but the customer. And as print providers will be quick to admit, customers have a habit of deciding just how good is good enough. Furthermore, if the customer pays the bill, goes away happy and comes back again, then the quality is probably just fine. "If its not sellable its not good enough," says Broadhurst. "Ultimately, quality is in the eyes of the customer," he adds.

This notion comes hard for some printers, but remember that the vast majority of customers are untrained in the nuances of printing and typically neither notice nor care about the subtleties of offset versus digital printing. They just want their job to look good and be delivered on time and on budget.

DMIA would like to thank Oce Printing Systems USA Inc., and Noel Ward for this contribution. (C)2002 Oce Printing Systems and Noel Ward

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