Absolute Color Measurement: Intelligent Systems Afford Seamless Quality Control

Competition in the printing industry is increasing and demands are growing constantly.

As such, precise inspection of the print image is a prerequisite for defect-free products and satisfied customers. In the packaging sector, high levels of color consistency in printing are required. Continuous color measurements and inspections are vital.

Whether for flexible packaging, personal care products or labels, brand owners only have minimal color tolerances, as perfect packaging and color uniformity are a firm part of the brand promise. Unfortunately, conventional measurement methods for absolute colors using a spectrophotometer have some disadvantages:

• The press has to be stopped each time, resulting in increased costs
• Very long measurement gaps prevent significant color deviations to be ruled out
• Print shops are faced with an incalculable risk—one that can cost large amounts of money, and damage their reputation with the customer

More challenging color designs are placing growing demands on process control and putting pressure on tight budgets. Today, a unique color management concept enables measurements to be made and repeated—at any point in the process and at any time.

An Intelligent Color Management Solution

Collection of absolute color measurement data, like that afforded by ISRA Vision’s ColorStar module for its standard inspection system, enables continuous monitoring of the color accuracy of printed products on presses without interrupting production.

Credit facilitation of data collection to the combination of a precise inline color line scan camera with a spectrophotometer, enabling continuous measurement and monitoring of absolute color values (L*a*b*). Measurements can be performed and repeated at any point in the process. As soon as printing commences, measured color values are continuously compared with the target specifications. Even the smallest deviations are detected in real time and corrected as quickly as possible.

Meanwhile, color trackers enable unlimited numbers of measurements to be performed per repeat. This intelligent concept allows print shops to observe and monitor color deviations while the web is in operation. As a result, automatic documentation of color measurement for every printed roll improves the printing process as a whole.

The new solution helps generate more value and serves to alleviate the challenge of the rapidly changing order structure in print shops. As jobs become smaller and smaller, makeready times are having a disproportionate impact. More effective preparation allows more jobs to be included in production planning, while the increased number of urgent jobs can be processed more efficiently thanks to the time gained.

Time & Waste Saver

The operator can adjust color without having to stop the press. As such, real-time measurements, enabled by perfect color measurement technology, reduce makeready times by up to 60 percent, thus lowering costs and reducing the amount of work involved.

The intelligent inspection system guarantees color consistency throughout the entire print batch in line with the brand owner’s specifications. Any deviations that reach a fully adjustable limit value immediately trigger an alarm. Continuous monitoring efficiently reduces waste and helps make the production process more sustainable and cost-efficient.

This inspection solution, used at any printing speed, is suitable for all substrates—even transparent, thin and stretchable ones. It automatically and continuously tracks measurement positions without any additional equipment. The solution uses specific algorithms for tracking and continuously recognizing preset measuring points.

As many brand owners require documented color consistency, the ColorSTAR inspection module guarantees complete and automatic documentation of every roll, while deviations between target and measured values are recorded and clearly displayed in an L*a*b* diagram. Moreover, the entire system has been designed to increase ease of operation: Thanks to the easy-to-understand Touch & Inspect GUI and self-calibrating spectrophotometer with adjustable calibration intervals, system operators do not require extensive training when installing the inspection system on site in the print shop.

Quick Makeready

The advantages of combining color line scan camera technology and a spectrophotometer are obvious. Absolute color measurement begins as early as the makeready process and improves workflow throughout production.

• The line cameras perform relative color measurements based on RGB values
• RGB values are then automatically converted to L*a*b* values in combination with a self-calibrating spectrophotometer
• A possible Delta E deviation from the target value is recognized during every repeat
• The operator can set the color during the makeready process without having to stop the press
• Makeready times and costs are effectively reduced

Digital Processing

The combination of line scan camera technology and spectrophotometers is the future of absolute color measurement. Integrated tools for data collection and reporting for production analyses are important components for achieving ideal print quality.

Decision makers can use the data collected by the quality assurance systems during optical inspections to gain valuable information on the quality and productivity of the production process. In doing so, they can also analyze the process using the EPROMI data mining software in order to continuously optimize production.

Real-time, perfect color measurements—everywhere and at all times—reduce makeready times and material costs.

About the Authors

Amir Dekel is vice president and business unit manager, Print Inspection at ISRA Vision GmbH. He has long been involved in supporting the print industry, with past experience at HP Indigo, Advanced Vision Technology, Pegasus Technologies and others.

Danilo Maugeri is product manager, print inspection and former vision expert. His career at ISRA Vision spans seven years. Earlier experience, dating back to 2004, includes stints as a production manager and printer, both at Bartsch International. That German firm specializes in security and continuous printing, as well as RFID technology.

Luciano Menk, sales manager for the Americas, is based in Atlanta, GA. With more than 15 years of experience in inspection solutions for the manufacturing and converting industries, his customers rely on his expertise for process and quality improvement through surface inspection. He has served ISRA Vision in different roles for approximately 10 years.Working alongside ISRA, researchers, they recently developed the ColorSTAR module that provides the firm’s standard inspection system, PrintSTAR, with absolute color measurement data. It combines the special benefits of spectrophotometric measurements with those from color line scan camera technology.