|
Business Printing Technologies Report TABLE OF CONTENTS The BPTR is best viewed through a web browser. <http://www.dmia.org/sol_center/bptr/02aug30_bptr.html>Click here to open this issue in your browser.
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. 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.
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.
"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."
Document Type: Trade books, manuals, directories, newsletters Document Type: Marketing materials Document Type: Basic bills, statements, etc. Document Type: Enhanced bills, statements with targeted marketing
messages Document Type: Hardcover books, magazines Document Type: Annual reports Figure 1: Documents and Expectations How Good is Good Enough? Subjective and Objective Measures 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.
Subjective Measures: Halftone quality Subjective Measures: Text clarity, sharpness Subjective Measures: Paper brightness Subjective Measures: Paper weight Subjective Measures: Consistency Subjective Measures: Repeatability
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 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"? 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 <http://www.oce.com/en/default.htm>Oce Printing Systems and Noel Ward Want to join a discussion on this article? <http://www.dmia.org/sol_center/UBBbptr/Forum22/HTML/000001.html>Click here to go directly to the BPTR Discussion Bulletin Board.
<http://www.dmia.org/cgi-bin/UBBbptr/Ultimate.cgi?action=intro>The
BPTR Discussion Bulletin Board is an online, interactive forum where you can
post messages, read messages and reply to messages related to topics discussed
in the Business Printing Technologies Report. At the end of each article in the
BPTR, you will find a link to a related discussion. Just click on those links to
go directly to that particular discussion forum. Once there, you can also check
out the "FAQ" link to read more details on the different features of the BPTR
Discussion Bulletin Board. Here's how to register: 1. Click on the "register" link near the top right of the BPTR
Discussion page.
EDITORIAL STAFF: <mailto:jgordon@dmia.org>
ADVERTISE:
|