This technical article Author: Raymond Cheydleur Rite global OEM technical manager Kevin O'Connor color consultant
Most modern printing and proofing papers contain optical brighteners (OBA). Such additives can increase brightness and improve appearance. Brighteners in modern paper pose challenges to successful color management. Therefore, the new standard is conducive to color management and communication of paper containing brighteners.
Introduction
Fluorescent brighteners work through fluorescence reactions. They absorbed invisible ultraviolet (UV) radiation with a wavelength below 400 nanometers, and released light waves through electrophysical changes. The wavelength was basically in the blue region of the visible spectrum between about 400 and 450 nm. Because under the illumination of a large amount of ultraviolet light, the observed light is the sum of reflected and emitted light, so this light has a whiter color than white after it is released from the paper containing the brightener. Such an effect can often be seen when illuminating paper containing whitening agents with ultraviolet light sources such as "black" light.
The paper printed on the base layer containing fluorescent whitening agent looks different in color, because it depends on whether the illumination light source used to view the printed matter contains ultraviolet light.
Early printing measurement standards (in addition to density standards) specified the illumination light source as D50. It is assumed that the substrates are all measured with D50, regardless of the composition of the optical brightener. In fact, under the actual observation conditions containing ultraviolet light, the colors seen are often not consistent and cannot meet the requirements. These deviations pose a major challenge to people trying to measure and manage color consistency in different workflows.
New technologies, new paper and new standards
New lighting sources, including light-emitting diodes (LEDs), allow portable color measuring instruments to use their well-defined and controlled UV light components for measurement. To ensure consistency, new light sources and new substrates require new instruments and new standards to define and measure UV light content, as well as the fluorescence of the fluorescent whitening agent contained in the substrate. It is very important to define and control the UV luminescence composition of the light source of the measuring equipment in order to define a standard method to measure and manage the color of the printed matter containing the fluorescent whitening agent substrate.
X-Rite has always actively promoted and committed to the forefront of design standards, and has always advocated the concept of "standard-based printing". Factors driving change include technological improvements, continuous dissemination of information from different media, and the need for printing suppliers and supply chain partners to increase efficiency, output, and profit.
A defined series of new measurement conditions
As part of ISO 13655-2009: Spectral measurement and chromaticity calculation of printed images, measurement of lighting conditions. The new measurement standard M series was stipulated by the International Standards Organization (ISO) and developed lighting conditions suitable for substrates containing different brightener standard.
The M series further improves the color management of substrates containing optical brighteners. Under different lighting sources, the color of materials containing fluorescent whitening agents will change, and the M series came into being.
The above chart shows the effect of three different lighting conditions on paper with and without optical brightener. As shown in Figure 2 below, the amount of change of the three lighting sources on the paper containing brighteners has led to a mismatch in most workflows and the inability to meet the requirements of customers in the printing industry.
In order to reduce this change and provide a communication method for measuring light sources, ISO13655 uses a new method of measuring light source conditions, which defines four different measurement lighting conditions. This representation method can also represent other measurement parameters such as polarized light. The M standard, as named, considers the conditions listed below.
Measurement condition M0
In the printing industry, most spectrophotometers and densitometers use incandescent lamps, whose spectrum is close to the International Lighting Association (CIE) standard lighting source A, and the color temperature is 2856K ± 100K. This is the expected condition of M0. M0 is limited to the concept, that is, the measurement lighting conditions are not fully defined, and the ultraviolet content of the light source is not determined. Because M0 also has a broader definition, including all instruments that are not applicable to other M conditions. For example, X-Rite and the former GretagMacbeth instruments have close consistency in the color temperature of the lighting source in the product line, which has been recognized and maintains good continuity with the lighting source A.
The measurement lighting condition M0 does not define the content of ultraviolet light. Therefore, when the measured paper contains fluorescence and the measurement data exchange between instruments is required, M0 is not recommended according to the provisions of ISO13655. The standard states that when there is no instrument that can meet M1, but the relative data is sufficient for process control or other data exchange applications, an instrument model like M0 can be used as an alternative. This clause ensures that existing instruments will not cause problems immediately and continue to be used in the workflow. At present, M0 instruments are very popular.
Measuring lighting conditions M1
The measurement lighting condition M1 is defined to reduce the difference in measurement results between different instruments due to fluorescence, which is caused by the fluorescent whitening agent of the paper, or the fluorescence in the imaging color or the proof color. M1 (Part 1) determines that the spectral power distribution of the measured sample illumination source should match the CIE illumination source D50. M1 also specifies a second method to meet the requirements of M1. (Part 2) This requirement only applies to the measurement of fluorescent whitening paper, not to the measurement of ink or fluorescent toner. This historical reason is because it is difficult to have a real D50 lighting source in portable instruments. The second definition only requires the use of compensating methods when adjusting the number of parts (spectral region below 400nm). This establishes a connection for the observation conditions of ISO 3664: 2009 and the defined D50 lighting conditions. The second method must be closely related to the observation conditions in accordance with ISO 3664: 2009, so use this method with caution and recommend testing to achieve agreement.
Measuring lighting conditions M2
For the first time, the ISO standard defines excluded UVs (known as UV-Cut, No UV, UV-Filtered) that should be included in measurement tools. M2 also provides tests that meet this standard. When customers require instruments that do not contain ultraviolet light, instrument manufacturers now have a clear method to reach agreement. We can measure paper containing fluorescent whitening agents and communicate color data more accurately and consistently. In the process of promoting XRGA, X-Rite has ensured that all new UV-Cut products meet this standard.
Measuring lighting conditions M3
M3 defines the polarization effect. In essence, M3 requires the UV-limiting properties of M2 and adds the definition of polarized light. Polarized light is used in some measuring instruments that eliminate or reduce specular reflection. Frequently, by selecting the polarization function or adding a manufacturer-specific polarization filter, the polarization standard is met. In the process of promoting XRGA (see below), X-Rite guarantees that the instrument that provides the M3 mode (polarization filter) can meet the new standard UV level.
Application of M0, M1, M2 and M3
• Theoretically, the use of each measurement lighting condition is relatively clear. • M0 is suitable for the case where neither the substrate nor the imaging colorant contains optical brighteners.
• M1, Part 1, is suitable for substrates, imaging colorants, or both containing optical brighteners.
• M1, part two, is suitable for substrates that contain fluorescence. The fluorescence characteristics need to be collected, and you can be sure that the imaging colorant does not contain fluorescence. (If in doubt, it is recommended to consult the ink manufacturer.)
• M2 is used for paper fluorescence, but it also hopes to eliminate the impact of data.
• M3 is used for special purposes, that is, it should reduce the reflection of the first surface, including the use of polarized light.
In practical applications, the boundaries of these use cases are not clear. Today, with the help of M0 instruments, all standard printing conditions in the industry have been established. According to the continuous use of substrates and inks with added optical brighteners, ISO is also examining this issue, but currently M0 has become the de facto standard measurement lighting condition in the printing industry.
Important factors to consider
To get the standard value, "print based on data", or meet the value provided by the customer, it is necessary to understand the source of the value. The density is less affected by the lighting source conditions, but when measuring paper and non-solid colors, it will cause a difference in density. Different state (T, E) response methods and / or the use of polarized light filters can make a big difference. When exchanging data, recording measurement lighting conditions (M0, M1, M2, M3) and chromaticity calculation methods (eg, D50 / 2, D65 / 10) are as important as recording density status.
X-Rite is working with ISO to define a more complete method, using the Color Exchange Format (CxF) for measurement data exchange. Our customers can trust X-Rite to provide a way to switch from traditional instruments to XRGA instruments. This includes all the measurement lighting requirements and conditions specified in ISO13655. However, before we started this event, X-Rite decided to help customers better manage the color data from our product family series. This commitment has recently been partially unfolded in XRGA and CxF. These technologies are designed to help reduce differences between X-Rite instruments and standardize file formats for digital color data exchange. Products that already include these technologies will help customers use the new ISO to measure lighting conditions (M0-M3) for better measurements.
X-Rite Printing Standard [XRGA]
X-Rite and the former GretagMacbeth have fully considered the historical status of the two and provided tools that meet the needs of their customers and meet ISO standards. Since the merger of X-Rite and GretagMacbeth, the new X-Rite has recognized the difference in measurement standards in the old product lines of the two companies. Both companies have traceable standards and procedures. X-Rite noticed that these differences are a problem for customers, especially those who use multiple measuring instruments or need data exchange.
XRGA is a calibration standard developed by New X-Rite for printed measuring instruments. The standard includes new developments in color technology and changes to meet ISO-13655 requirements. The aim is to ensure that our preferred product portfolio allows all customers, regardless of whether the instrument is new or old, to enjoy high-quality data exchange in the workflow of different instruments.
X-Rite Printing Standard [XRGA]:
• Includes the best category method in measurement • Traceable to the National Institute of Standards and Technology (NIST)
• Compatible with existing ISO standard 13655 • Improve the inter-station agreement of existing instruments • Retain the agreement between former X-Rite and GretagMacbeth instruments • Provide a single standard for X-Rite measuring instruments
The new printed measuring instruments are compatible with XRGA, and existing instruments will also be compatible with XRGA when returning to X-Rite for annual verification.
CxF3
CxF3 specifies an XML (Extensible Markup Language) based on the color specification mechanism, which is comprehensive, flexible, and applicable to various industries where color and appearance data exchange is vital. CxF utilizes the openness and wide acceptance of XML, so it can be seamlessly integrated in any workflow. By using XML, CxF provides self-identifying color data and establishes a flexible communication mechanism. CxF can seamlessly integrate data obtained using other color communication methods, including ICC color profiles, density, CIE-Lab, XYZ, RGB, CMYK, PANTONE, RAL, NCS, Toyo, HKS, etc. CxF is currently a theme of the development process of the ISO standard, covered under a comprehensive topic: ISO17972 flat image technology-color technology exchange format (CxF / X)
in conclusion
X-Rite will continue to support the formulation and revision of new industry standards. To this end, we help customers and the entire industry to improve quality and promote prosperity to a new height. We are honored to work with outstanding talents in multiple workflows and look forward to continuing to support the industry with the world's best measurement tools in the printing industry.
About the author
Ray Cheydleur has worked in X-Rite for more than ten years, and has worked in the fields of imaging, printing and process control for more than 30 years. Ray is the chairman of the ANSI-approved Image Technology and Standards Committee (CGATS) and the chairman of CGATS SC3 for metrology and process control. Ray also participates in ISO printing and image standards as a representative of the United States.
Kevin O'Connor has been in the color industry for many years as a photographer, designer, product manager, speaker and educator. He blends Irish wisdom and love of language into his work enthusiasm, and conveys complex color concepts in an easy-to-understand way.
Professional noun list
CGATS: Graphic Arts Technologies Standards
CxF: Color Exchange Format
D50: Daylight 5000K Daylight 5000 Kelvin
ISO: International Organization Standards
LED: Light emitting diodes
M: Measurement Mode
Nm: Nanometers
UV: Ultraviolet
XML: eXtensible Markup Language
XRGA: X-Rite Graphic Arts Standards
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