Quality Control: Measure it, Control it!
The value in quantifying printing variables, beginning in prepress, can be seen in consistent, repeatable color reproduction.
September 2006 by Jean Marie Hershey
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The roles of quality control (QC) equipment and systems in the pressroom and in the prepress area are related, but distinct. By the same token, color management and color process control are related, but are separate concepts. While color management means managing your devices such that you output color accurately and consistently, quality control or color process control ensures that the color will be consistent across processes and substrates. QC clearly represents a very specific challenge in packaging, given the variety of different substrates and disciplines commonly applied to a given brand.
Nevertheless, color process control has had a tough row to hoe for packaging printers, who initially failed to understand the need for robust, reliable instrumentation designed to verify and calibrate the output of their computer-to-plate systems. This month, packagePRINTING speaks with several instrument suppliers to clarify some of the issues surrounding the role of color process control in enhancing reproduction quality, color control, and productivity.
Risky business
According to Larry Goldberg, director of engineering for Beta Industries, for the many thousands of pieces of output created every hour in the pressroom, a variety of simple or sophisticated QC measures can be applied. These include statistical sampling or visual inspection and density spot checks or full sheet scans, depending on the customer’s expectations and the capabilities of the pressroom, where it is generally accepted that some waste and spoilage will occur. In contrast, materials created in the prepress department carry a much higher risk. “For example,” Goldberg says, “a bad plate can idle a press chargeable at hundreds of dollars per hour. Even when a plate appears usable, precious time is often wasted tweaking it on press, even adjusting inks or anilox rolls.”
To alleviate these risks, different instruments, including densitometers, colorimeters, spectrophotometers, and plate analyzers, were developed to detect and measure color changes at various stages in the workflow. Densitometers determine the strength of a color from its density, usually derived from ink film thickness. Colorimeters, such as X-Rite’s 528 handheld unit, break down color into its numeric value using the CIE XYZ color space or one of its derivatives, such as CIE L*a*b or CIE L*u*v. Spectrophotometers measure spectral data, which form a complex set of data on the spectral curve. Spectrophotometers gather the most complete color data and provide the most accurate and useful color information.
Nevertheless, color process control has had a tough row to hoe for packaging printers, who initially failed to understand the need for robust, reliable instrumentation designed to verify and calibrate the output of their computer-to-plate systems. This month, packagePRINTING speaks with several instrument suppliers to clarify some of the issues surrounding the role of color process control in enhancing reproduction quality, color control, and productivity.
Risky business
According to Larry Goldberg, director of engineering for Beta Industries, for the many thousands of pieces of output created every hour in the pressroom, a variety of simple or sophisticated QC measures can be applied. These include statistical sampling or visual inspection and density spot checks or full sheet scans, depending on the customer’s expectations and the capabilities of the pressroom, where it is generally accepted that some waste and spoilage will occur. In contrast, materials created in the prepress department carry a much higher risk. “For example,” Goldberg says, “a bad plate can idle a press chargeable at hundreds of dollars per hour. Even when a plate appears usable, precious time is often wasted tweaking it on press, even adjusting inks or anilox rolls.”
To alleviate these risks, different instruments, including densitometers, colorimeters, spectrophotometers, and plate analyzers, were developed to detect and measure color changes at various stages in the workflow. Densitometers determine the strength of a color from its density, usually derived from ink film thickness. Colorimeters, such as X-Rite’s 528 handheld unit, break down color into its numeric value using the CIE XYZ color space or one of its derivatives, such as CIE L*a*b or CIE L*u*v. Spectrophotometers measure spectral data, which form a complex set of data on the spectral curve. Spectrophotometers gather the most complete color data and provide the most accurate and useful color information.
Companies Mentioned:
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Color Management Handbook: A Practical Guide
Nine Steps to Effective and Efficient Press OKs