A letter from the Editor
This issue of the Journal is being created right before the joint conferences of iarigai and IC, two important international print and media associations, involving academic, research and educational organizations, as well as industrial enterprises and institutes. Expectations are optimistic, as the organizers announced the participation of numerous recognized researchers and experts who will present their latest results and achievements.
The results of previous research, partly already presented at the conferences, are also published in this third 2018 issue of the Journal. Two research papers are the work of the same authors, but they cover quite different topics, although both of them are related to the quality of color reproduction in the print proces. The first paper deals with the new spectral trapping model in halftoning, which represents an improvement of well-known and widely used halftoning in prepress workflow, based on the improved Demichel and Neugebauer mathematical models. Considering trapping given as a color difference in halftoned patches of secondary and tertiary colors, a model with a potential for improving the quality of four-color reproduction in the press is shown.
The second paper deals with an improved automated CtP calibration model for offset printing. With the proposed enhancement, it is possible to correct the rendering of the printing forms in view of the changes in the materials used for printing and in the printing machine settings. Based on the spectrophotometric measurements of a relatively small number of control patches, sufficient data are obtained to make changes in the settings of RIP, which is an integral part of the CtP Workflow system, to achieve the optimal rendering of the printing plates under given print conditions.
The third research article shows the process of optimizing the production of printed chipless RFID tag, as a necessary condition for the implementation of this modern coding system in wide use, potentially even as a replacement or upgrade of established barcodes and 2D codes. The emphasis is on sintering methods that, under normal conditions of use (wireless communication quality, speed, price), can help to achieve technically appropriate and also market-acceptable production of RFID tags, and the results presented are promising.
This time the Topicalities bring an overview of the latest standards adopted by ISO TC 130 – Graphic technology and news on international research activities and the new Master of Engineering degree in Printed Intelligence. The review of new books covers the fields of image quality and typography as well as materials, photovoltaics, and packaging. A new edition of the book Introduction to Graphic Communication is presented, which also gives an interactive experience to the reader, however, with some initial issues. Associate editor Markéta Držková (email@example.com), who edited and composed the Topicalities, also chose three interesting doctoral dissertations, even from the universities less known in our research community. At TU Darmstadt, IDD, Maximillian Klammer defended the thesis on the use of CCD line camera as a measuring device for color and stereoscopic measurement. David Joseph Finn successfully defended the thesis in the field of inkjet printing of nanomaterials on flexible temperature sensitive substrates at Trinity College, Dublin. The third presented doctoral thesis by Nouran Yehia Adly, defended at RWTH Aachen University, is also based on a research on inkjet printing, this time for the production of electrochemical devices for bioelectronics.
The overview of conferences and symposia in the autumn period begins with already mentioned 45th International iarigai Conference and the 50th International Circle Conference, which both take place in Warsaw, where the Department of Printing Technology of the Warsaw University of Technology celebrates the 50th anniversary. We could expect a number of interesting new contributions and some of the authors already expressed their interest in publishing full, revised and extended papers in the Journal, after the Conferences.
During the course of the two conferences, activities will also be undertaken to improve the content and recognition of the Journal as one of the key channels for publishing the results of scientific and research work in the area it covers. The results should be visible in the forthcoming issues.
Ljubljana, September 2018
A novel spectral trapping model for color halftones
Sasan Gooran1and Shahram Hauck2
E-mails: firstname.lastname@example.org; email@example.com
1Dept. of Science and Technology, Linköping University, Campus Norrköping, 601 74 Norrköping, Sweden
2Dept. of Informatics and Media, Beuth University of Applied Sciences Berlin, Luxemburger Straße 10, 13353 Berlin, Germany
The amount of trapping has a great impact on the gray balance and color reproduction of printed products. The conventional trapping models are print density based and give percentage values to estimate the effect of trapping. In an earlier research, a spectral trapping model was proposed, that defines the trapping effect as the ∆E*abcolorimetric differences between the real ink overlap (measurements) and the ideal ink overlap. All the trapping models proposed so far, however, only calculate the trapping value for full-tone (solid) ink overlap. As the trapping value for full-tone ink overlap could be overestimating the actual ink trapping effect for halftones, it is important to be able to also approximate the trapping value of color halftones. Furthermore, for a detailed gray balance shift analysis, there is a need to estimate the trapping effect for specific color halftones. In the present paper, we propose a novel spectral trapping model that delivers the trapping value as ∆E*abcolor difference for color halftones taking into account secondary and tertiary ink overlap. The results of the experiments show that the trapping values for color halftones are much smaller than the corresponding trapping value at full tone. The trapping value of halftones, besides other common quality parameters, should still be considered if some quality inaccuracy, such as gray balance shift, occurs in a print production.
Keywords: ink trapping, halftoning, gray balance, color difference (∆E*ab), printing quality
JPMTR 110 | 1811 Research paper
Automated CtP calibration system in an offset printing workflow
Although offset printing has been and still is the most common printing technology for color print productions, its print productions are subject to variations due to environmental and process parameters. Therefore, it is very important to frequently control the print production quality criteria in order to make the process predictable, reproducible and stable. One of the most important parts in a modern industrial offset printing process is Computer to Plate (CtP), used for printing plate production. One of the most important quality criteria for printing is to control the dot gain level. It is crucial to have the dot gain level within an acceptable range, defined by ISO 12647-2:2013. This is done by dot gain compensation methods in the Raster Image Processor (RIP). Dot gain compensation, which is also referred to as CtP calibration is, however, a complicated task in offset printing because of the huge number of parameters affecting dot gain. The conventional CtP calibration methods for an offset printing process, which are very time and resource demanding and hence expensive, mostly use one to five dot gain correction curves as the maximum. The proposed CtP calibration method in this paper calibrates the dot gain according to ISO 12647-2:2013 recommendations fully automatically parallel to the print production. Besides that, there is no limitation of the number of the needed dot gain correction curves. This automated CtP calibration method, which is much more efficient and economically beneficial compared to conventional CtP calibration methods, also makes the printing production very accurate in terms of dot gain value.
Keywords: workflow control system, printing process variables, ISO 12647-2:2013, dot gain compensation, raster image processor
JPMTR 111 | 1808 Research paper
Effect of printing parameters on microwave performance of printed chipless RFID tags
Sika Shrestha and Nemai Chandra Karmakar
E-mails: firstname.lastname@example.org; email@example.com
Department of Electrical and Computer System Engineering, Monash University, Australia
The chipless Radio Frequency Identification system (RFID) will revolutionize the identification market due to its low-cost tagging methods. The printed version of the chipless tag is able to reduce the cost to few cents per tag. The microwave performance of the printed chipless tag is suffered due to the practical limitations of the overall fabrication procedure through printing. The bandwidth broadening is unavoidable for the printed tag, which directly hits on the data capacity. Similarly, the strength of the microwave signal is also degraded for printed RFID tag, which affects the reading distance of the tag. The fabrication of chipless RFID tag via printing involves several parameters such as the conductive ink processing condition, the substrate parameters and the geometrical dimension of the printed tag. We need to understand the relationship between these printing parameters with the microwave response of the printed tag, to analyze the key parameters affecting the response of the printed tag. A comprehensive experimental investigation is performed in this paper to evaluate the relationship between the printing parameters and microwave response of the printed tag. The printing parameters include conductive ink sintering type and sintering conditions and deposited ink thickness. A high-speed photonic sintering process is adopted for the first time to sinter chipless RFID tag so that chipless RFID tag can be manufactured using fast roll-to-roll printing process. Optimum conditions for the photon-sintering process are deduced through experimental analysis for conductive inks of various viscosity. The effect of the geometrical dimensions of the printed strip and the printing accuracy is also analyzed to understand the limitations of the printing technique in terms of tag size. The issues seen in the printed RFID tag, their reason and the solution is then deduced in the final section so that the printed chipless tag can accommodate the real world limitations to make viable commercial outcome.
Keywords: RFID communication, screen-printing technology, conductive ink, oven sintering, photon sintering
JPMTR 112 | 1812 Research paper