ISO 24585-2:2023

Graphic technology — Multispectral imaging measurement and colorimetric computation for graphic arts and industrial application — Part 2: Requirements for decorative surfaces

This document specifies requirements for multispectral imaging devices to measure and compare the decorative surfaces. Based on spatially resolved spectral measurement of reflecting surfaces, tristimulus images are computed. A metric is provided that reflects the visual closeness between a reference surface and a comparison surface using a single index called SIM_PDE. Recommendations are provided with regard to laboratory sample preparation. This document is not applicable to functional surfaces.

Technologie graphique — Mesure multispectrale et calcul colorimétrique pour les arts graphiques et les applications industrielles — Partie 2: Exigences pour les surfaces décoratives

General Information

• Status: Published
• Publication Date: 24-Sep-2023
• ICS: 37.100.01 - Graphic technology in general
• Technical Committee: ISO/TC 130 - Graphic technology
• Drafting Committee: ISO/TC 130 - Graphic technology
• Current Stage: 6060 - International Standard published
• Start Date: 25-Sep-2023
• Due Date: 13-Dec-2024
• Completion Date: 25-Sep-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 24585-2
First edition
2023-09
Graphic technology — Multispectral
imaging measurement and
colorimetric computation for graphic
arts and industrial application —
Part 2:
Requirements for decorative surfaces
Reference number
© ISO 2023
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Multispectral measurement requirements . 2
4.1 Instrument standardization and adjustment . 2
4.2 Illumination requirements . 2
4.2.1 Wavelength range . . 2
4.2.2 Measurement conditions . 2
4.3 Specimen preparation and backing requirements . 3
4.4 Light capturing requirements . 3
4.4.1 Spatial resolution . 3
4.4.2 Wavelength range, wavelength interval and bandwidth . 3
4.5 Multispectral image storage . 4
4.6 Tristimulus image computation requirements. 4
4.7 Requirements for comparing multispectral images . 4
4.8 Requirements for comparing tristimulus images derived from multispectral
images. 4
4.8.1 General . 4
4.8.2 Comparison method . 4
5 Data reporting requirements.6
6 Conformance . 7
Annex A (informative) Checklist for specimen preparation . 8
Bibliography .10
iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 130, Graphic technology.
A list of all parts in the ISO 24585 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
In the wood products industry, wood-based panels, for use as furniture or flooring components, are
prepared by impregnating a printed base paper with an artificial resin, and then laminating it to a
chipboard or fibreboard base by curing the resin using high temperature and pressure. In the decorative
printing industry, the base papers are often printed with a simulation like a woodgrain or other natural
material.
The assessment of the appearance of such prints during the make-ready and for re-prints have long
been done using trial and error. It is common to take a master pattern provided by a customer and
to reproduce it. The visual agreement between the master and the reproduction is normally carried
out by experienced personnel who visually compare the target and the production, under controlled
illumination conditions, using either D65- or D50-like illumination. The necessary changes to improve
[1]
the visual match were manual recipe updates in the ink kitchen in case of rotogravure printing or
manual adjustment of image artwork on calibrated monitors in case of digital printing.
Conventional point measurement devices are occasionally used to objectify the assessment, but their
field of view was too large to resolve fine detail and repositioning was also challenging. Such manual
and subjective methods gave satisfactory results for the production, but it has the following problems:
— it requires specially trained personnel requiring a long training phase;
— the results of the judgments change over time due to observer fatigue;
— the master aim changes its colours over time for many reasons; and
— the subjective assessment gives rise for debates in cases of dispute.
Multispectral imaging devices were introduced to wood lamination production around the year
[2] [3],[4]
2010 to improve both process control and quality assurance . First, the spatial resolved inline
capturing allowed for a pixel-by-pixel comparison between the master and the pertinent reproduction.
Given an appropriate image registration and spectral accuracy multispectral imaging systems allowed
for an objective evaluation of the image differences including aspects such as local contrast. Such a
comparison typically leads to two different outcomes. On the one hand, a single number index is
condensed to uniquely define the visual closeness, which eases communication with customer and the
agreement of tolerance schemas. On the other hand, the comparison of tristimulus images leads to a
plethora of individual colour difference vectors that can be adapted to the individual press technology
to provide guidance for process control and the ink formulation. In both cases, it reduces scads of
measurement data (spectra of each pixel in a revolution as measured over a full press run) down to a
digestible amount of human and process control information. A single point measurement system is not
[5]
able to provide this information . This objective assessment can be used for both conventional and
digital production of the final panels.
For digital printing presses, which are increasingly used in that industry, the spatial colour difference
can be used to alter the image data in the RIP while printing. This improves the visual closeness
noticeably and is sometimes called colour looping.
This document defines the requirements for multispectral imaging systems which are needed for the
use case of decorative lamination and includes the introduction of an image similarity index, termed
SIM_PDE.
Since the sample preparation has an impact on the final product, this document provides guidance
with respect to the laboratory preparation of samples, to allow interoperability in the development of
process automation in the assessment of the appearance of the print.
v
INTERNATIONAL STANDARD ISO 24585-2:2023(E)
Graphic technology — Multispectral imaging measurement
and colorimetric computation for graphic arts and
industrial application —
Part 2:
Requirements for decorative surfaces
1 Scope
This document specifies requirements for multispectral imaging devices to measure and compare
the decorative surfaces. Based on spatially resolved spectral measurement of reflecting surfaces,
tristimulus images are computed. A metric is provided that reflects the visual closeness between a
reference surface and a comparison surface using a single index called SIM_PDE. Recommendations are
provided with regard to laboratory sample preparation.
This document is not applicable to functional surfaces.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
ISO 24585-1, Graphic technology — Multispectral measurement and colorimetric computation for graphic
arts and industrial applications — Part 1 Parameters and measurement methods
ISO 28178, Graphic technology — Exchange format for colour and process control data using XML or ASCII
text
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 24585-1 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
decorative surfaces
base papers, printed with a simulation like a woodgrain or other design
Note 1 to entry: Decorative surfaces are usually created in the decorative printing industry. They show either
a uniform colour or a texture of some kind. Decorative surfaces are typically not showing a high level of
fluorescence.
3.2
specimen backing
material placed behind and in contact with the specimen during measurement
Note 1 to entry: This can be white, black or the same material as the specimen self.
3.3
SIM_PDE
index of similarity between a reference image and a test image based on the average colour difference
between two identically specified sets of patches
3.4
shading correction
method for adjusting intensity levels in a digital or electronic image, caused by non-uniformities in the
illuminating or detecting systems
[SOURCE: ISO 10934:2020, 3.2.44]
4 Multispectral measurement requirements
4.1 Instrument standardization and adjustment
The measurement device or system shall be standardized and possibly adjusted in accordance with its
manufacturer's instructions.
[6]
NOTE 1 ISO 15790 defines the use of a certified reference material (CRM) to check calibration of a
measurement system. It also provides additional information relating to the use of CRMs, the determination of
combined standard uncertainty and data reporting.
NOTE 2 Where multiple instruments are used for measurement, there can be differences in the resulting data
due to the individual characteristics of the instruments and variations in measurement conditions.
4.2 Illumination requirements
4.2.1 Wavelength range
The spectral power distribution shall have sufficient energy at all wavelengths in the range from
400 nm to 700 nm inclusive to make measurements with low noise.
4.2.2 Measurement conditions
The measurement area should be visually uniform. Within the reference plane the measurement area
shall be assessed at least at 100 equally spaced measurement positions. The illuminance or luminance
should be within 5 % of the average value and shall be within 25 % of the average value.
NOTE 1 The uniformity can be assessed by using an imaging luminance measurement device as described in
Reference [7].
NOTE 2 A shading correction is always applied to improve uniformity. In order to retain appropriate signal to
noise ratio, this compensation is restricted.
The spectral power distribution of the illumination shall be continuous across the visible range and
should exclude the radiant power at wavelengths below the visible spectrum. ISO 13655 describes one
way to achieve this by filtering the shorter wavelengths from a source that has radiant power at all
wavelengths in the range from 420 nm to at least 700 nm and is noted as M2, UV cut.
NOTE 3 Most specimens tested in this document do not show any significant amount of fluorescence, any
instrument source with low levels of light of shorter wavelengths will suffice, including incandescent sources and
LED sources that utilize only visible range LEDs and phosphors.
Departures from these nominal requirements shall be reported.
The measurement geometry of the imaging system shall be 45°:0° (influx: efflux). The efflux optics shall
be oriented along the normal to the surface of the substrate in the reference plane. The tolerances for
[8]
the efflux optics given in CIE 176 should be met at the centre of the field of view. Unidirectional or bi-
directional influx geometry may be used, though this is a departure from CIE 176.
While being measured the specimen shall lie on a flat surface in the reference plane, e.g., a roller for an
inline measurement system. The instrument reference plane and the specimen surface shall lie in the
same plane.
NOTE 4 Imaging systems inherently work with an area illuminated being larger than the measured area,
known as overfilling.
4.3 Specimen preparation and backing requirements
The specimen shall be backed by either a black or a white material that conforms to ISO 13655. Where
specimens being measured by reflection are not fully opaque, the backing used should be characterized
and the method shown in ISO 13655 or Reference [9] may be used to correct such measurements to a
white backing reference.
NOTE For guidance concerning which specimen backing material to use
...