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Quality-control DOs and DON'Ts

Jul 1, 2003 12:00 AM


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Printers may have little control over the manufacturing quality of pressroom materials, such as paper, blankets, inks, plates and rollers. And few can afford to spend the time and money to conduct extensive in-house testing on these materials. GATF's (Sewickley, PA) experts offer the following dos and don'ts to minimize problems before a job is on press.

Scan and snap right

Don't scan images without proper scaling and reproduction characteristics | “Scanning an image without knowing the exact scaling and line screen of the final print can lead to improper usage of the image in the page layout, ultimately leading to printing problems,” says Greg Bassinger, GATF technical consultant.

Bassinger explains that if you were to scan an image with a total ink limit set to 380 percent coverage and have the image appear in a newspaper, the result would be a serious over-inking problem for the press crew. Other problems can come from improper resolution in the scanned digital image — such as moiré of patterns — if the image is to be scaled in a page-layout program.

Bassinger suggests scanning the image using a neutral carbon-gray wedge to optimize the color-sensing capabilities of the scanning device. He also suggests that you scan with enough resolution to support the line screen and printing technique. Setting proper contrast levels during the scan ensures the best possible reproduction.

Don't use the camera software to correct for bad lighting and exposure | Bassinger, who also teaches a workshop on digital photography for print at GATF, notes that it has become easy to “correct” for difficult lighting conditions and exposures, since the digital camera's software can allow for tone manipulation and compression during the capturing process. In reality, he says, the digital information is being altered to fit what is thought to be a better-looking shot, often one on a monitor. Proper lighting and exposure should therefore be used to solve image-related problems before capturing the image.

GATF suggests you should always capture images with the proper gray balance in the photograph. The use of a grayscale or gray card is essential for gray balance. Even if the reference cannot be included in the scene and passed along to the next step, it should be used to neutralize the scene being photographed, before capture. The information should then be passed along through the workflow to ensure proper handling of the file, rather than have someone else decide the image's color balance.

Standards for quality

Do set standards for accepting digital files, and do educate your clients | Digital files intended for eventual print production are supplied in a dizzying array of formats, from native-application files to PostScript, PDF, TIFF/IT or DCS/EPS files.

Interestingly, in a time when some publishers are requiring very specific files for digital ad submission, such as TIFF/IT or PDF/ X-1a, many general commercial printers seem to have adopted a “we'll take anything to get the job in the door” approach.

“If we look at incoming digital files as a raw material in a production process, then allowing them to come into your shop incorrect is akin to accepting flawed paper or ink in the pressroom,” says Julie Shaffer, director of the Robert Howard Center for Imaging Excellence at GATF. To take control of the files supplied to you, she suggests that you supply customers with the tools they need to create quality files for submission. This can be as simple as providing custom Acrobat Distiller job options for the creation of PDF files based on your production requirements.

Along with the job options, you must supply the correct driver, printer-description file and instructions on the best way to use them to create print-quality PDF files. There are tools available that also allow a means to preflight and even correct a project at the same time that the PDF file is created. When printing PDFs created by Enfocus Software's (San Mateo, CA) Instant PDF to a desktop printer, for example, the project is run through a preflight check based on Enfocus Pitstop profiles as a part of the process. Based on the profile settings, this process can include fixes like automatically converting RGB images to CMYK, or the creation of a PDF/X-1a standard PDF file.

PDFs and proof viewing

Do invest in new technologies to alleviate time-consuming and costly problems | Many prepress professionals complain that, even when instructions on how to create files properly are provided along with tools like Distiller job options, clients sometimes don't use them. In response, Adobe Systems Inc.'s (San Jose, CA) PDFTransit and Global Graphics' (Waltham, MA) PDFCourier leverage the ubiquity of the Internet to literally control how the designer creates and delivers content to the output provider. “Using these tools, the designer simply prints to a supplied virtual printer, which in turn checks, corrects, compresses and sends the job to the printer — all in one neat package,” explains Schaffer, who is co-author of GATF's The PDF Print Production Guide.

Don't view proofs under your desk light | Communicating the phenomenon called color is difficult. In order to reduce variables in the color-communication process, you must view color under consistent conditions: a color-viewing booth.

Joe Marin, co-author of The PDF Print Production Guide, says that North America uses American National Standards Institute viewing conditions. The lighting is 5,000° Kelvin and the surround color is Munsell N-8 gray, a neutral shade taken from the Munsell Color Tree. This is important because the surrounding environment in which you view proofs will dramatically affect the color perceived on the proof.

The temperature of the light source is also extremely important in determining what color the viewer sees. The same proof will look very different under different lighting conditions. Experts suggest 5,000° Kelvin lighting because it emits an equal (neutral) mix of red, green and blue wavelengths of light. GATF's RHEM light indicator can be used to verify if lighting is 5,000° Kelvin — when placed directly on the proof, the device will appear solid when the lighting conditions are 5,000° Kelvin, and will show stripes when the lighting is not.

Perfect proofs, plates

Do make sure each proof is correct | Marin explains, “Color proofing works when it is consistent and repeatable. But you must measure it to verify these factors.” Using targets for the initial calibration of a proofing system is only part of the process; a measurable target must be on every proof to ensure its accuracy.

Specifications for Web Offset Publications (SWOP) recommends that a GATF/SWOP Proofing Bar and/or GATF/GCA Proof Comparator appear on every off-press proof to be SWOP-certified. These targets are ideal for evaluating the accuracy and consistency of color proofs. They are available in digital format so that they can easily be placed within a standard layout or imposition template.

The GATF/GCA Proof Comparator, for example, allows for the measurement of dot gain, gray balance, trap, highlight and shadow dots, and many other conditions, all within a compact target. In addition to these measurable print attributes, there are also components within the target that can be used to assess color visually. By placing a target on every proof and measuring these print attributes, you and your customers can be assured that the color is accurate.

Do make sure you obtain accurate film percentages | Dan Remaley, a GATF process-controls expert, reminds printers to use a transmission densitometer to measure the dot percent value of film output or tonal areas within a separation or screen tint. “Measurable and repeatable values are imperative,” he says. The values are actual printing dot percentages. The imagesetter films should be linear in value — a 50 percent value in a digital file should equal 50 percent on film. For example, Pantone Inc.'s (Carlstadt, NJ) “Solid to Process” Color Guide uses screen builds based on percentages of CMYK to approximate the Pantone PMS Colors. These values, when printed correctly, will match the Pantone book.

Don't overexpose a plate to emphasize highlight dots | Printers tend to overexpose a plate because they are concerned that the tiny highlight dot won't hold up in the printing process. “This may help the highlight (one percent to two percent) dot, but at the sacrifice of the midtone (50 percent) dot, which is more sensitive,” Remaley warns. “The measurement of midtone dot gain is one of the most important numbers to record and evaluate. It determines the print characteristics of the press and its relationship to the proof, or any SWOP or General Requirements for Application in Offset Lithography (GRACoL) requirement.” At an optimum exposure of six to eight microns (for most plate products), a 50 percent dot will become 54 percent when measured on the plate. An overexposed plate will measure 58 percent to 60 percent in the 50 percent target area. This overexposure will cause excessive dot gain on press and will make images appear darker than on the proof. GATF offers printers its Plate Control Target or a UGRA Plate Wedge to properly measure exposure.

Control equals consistency

All of GATF's experts agree that without controls in every department of the plant, you won't have an accurate idea of how the final product will look. If you don't specify, measure and control, the final product will be unpredictable. When the printing manufacturing process is controlled, the resulting printed products are not only consistent, but you will also see positive effects on customer satisfaction, productivity, quality and cost.