ISO 13655
The ISO standard ISO 13655 describes the “spectral measurement and colorimetric calculation for graphic objects” for the printing industry. The current edition was published in August 2017 after the standard, which was significantly expanded in 2009 and revised in 2013, had been updated in some details between December 2014 and June 2017.
In Germany, which was standard ISO 13655: 1996 as DIN standard DIN published ISO 13655, but this was withdrawn in August 2010 without replacement.
Most important requirements
The following requirements are set for the measurement:
- The measuring instrument ( spectrophotometer , Spektraldensitometer ) should be calibrated and the wavelength range 380 to 780 nm in 10-nm increments covering, which is to cover a wavelength range 400 to 700 nm and at least in 10-nm increments measure needs .
- The measurement geometry 45 °: 0 ° or 0 °: 45 ° is to be designed with circular (from at least three directions), better annular (ring-shaped) illumination or detection due to the fact that the measurement is not directional.
- The color values are calculated on the basis of CIE light type D50 ( standard light ) and CIE standard valence system 1931 with a 2 ° standard observer.
The 2009 edition was of fundamental importance for the further development of the measuring devices. Because the gas-filled incandescent lamp with tungsten filament previously used as measuring light , the emission spectrum of which largely corresponds to standard illuminant A (mode M0) , i.e. only a low UV component but a high infrared component, was completely unsuitable for the physical simulation now required by the CIE -Light type D50 (mode M1) . Konica Minolta , Barbieri electronic and Techkon were the first manufacturers of measuring devices to replace incandescent lamps with LEDs , which, in their interaction with one another and in cooperation with the spectral sensitivity of the sensors (fulfillment of the Luther requirement ), can display the spectral radiation distribution including the UV component. The expanded or renewed definition of the measurement modes was necessary in order to better evaluate the increasing use of optical brighteners in paper and cardboard and to better predict their effect in the printing process.
Overview of the measurement modes defined in 2009 - practical interpretation of Chapter 4.2.2 Illumination requirements and measurement conditions :
| mode | Applications | Settings of the measuring device | Spectral range | UV component |
|---|---|---|---|---|
| M0 , "A" | Conventional color measurement : printed and colored surfaces, process control in prepress and pressroom, creation of ICC output profiles | Spectral remission factor without polarizing filter under a gas-filled tungsten incandescent lamp , which generates approximately standard illuminant A (incandescent lamp light with the most similar color temperature 2856 K ± 100 K) to simulate other types of light | from 380 nm (mandatory from 400 nm) to at least 700 nm | can be supplemented mathematically if necessary |
| M1 , "D50" | Physically correct color measurement : printed and solid-colored surfaces, process control in prepress and pressroom, creation of high-quality ICC profiles for digital proofs and printing processes | Spectral reflectance without a polarizing filter under a light source that physically simulates the standard light type D50 (artificial daylight, closest color temperature 5003 K ± 100 K) with the correct UV component | Excitation from approx. 300 nm, measurement from 380 nm (mandatory from 400 nm) to at least 700 nm | Connection of a UV source required; Transition of the D50 radiation distribution from UV to visible as CIE- compliant as possible between 300 nm and 500 nm |
| M2 , "UV-Cut" | Color measurement by hiding the UV component in the measuring light | Spectral reflectance without a polarizing filter under a light source that generates or simulates any type of standard light without a UV component or, if necessary, excludes the UV component with a UV blocking filter | from 380 nm (mandatory from 400 nm) to at least 700 nm | suppressed or switched off |
| M1 - M2 | physically correct color measurement to show the effect of optical brighteners (quantitative in%, qualitative as difference spectrum): creation of high-quality ICC paper profiles, evaluation of fluorescent printing inks | one after the other M1 and M2 (see there); Comparison made internally in the measuring device or externally in software of M1 (D50 with UV component in the measuring light) and M2 (here also D50 because of the comparability, but without UV component in the measuring light) | see M1 and M2 | isolated evaluation of the UV effect |
| M3 , "polarizing filter" | Densitometry : optical density (blackening), color density (process printing inks), spectral density (special colors); Color measurement : intensive scales, effect pigment colors, printing ink formulation | selective degree of absorption (under RGB + V vis filter set) or spectral degree of absorption (with spectral measuring head), each with a polarization filter pair (in the incident and in the reflected light, crossed with each other) under a light source that simulates any type of standard light | from a maximum of 420 nm to at least 700 nm | suppressed or switched off |
The 2017 edition redefines the properties of the white measurement base. Their values are now for transparent samples, for example clear transparent packaging films. In principle, either the white or the black base is to be used (the selection criteria are mainly defined in the parts of ISO 12647 and can also be found in the print media standard ). The "self backing", that means placing several sheets of the sample paper underneath to eliminate the influence of the measurement underlay, is only permitted in the paper industry. Furthermore, the requirements for the technical implementation of the M1 measurement mode have been made more precise, and unnecessarily large bandpass intervals and the outdated zero adjustment method for the reflection factor of fluorescent samples have been banned.