Yung-Cheng Hsieh, Hui-Wen Cheng

Department of Graphic Communication Arts, National Taiwan University of Arts
59, Section 1, Ta-Kuang Rd., Pan-Chiao City
Taipei County, Taiwan R.O.C.
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Abstract
This study investigates the use of AM/FM hybrid screening in conjunction with computer to plate (CTP) technology in order to obtain an optimum hybrid screening combination for the flexography printing process. The study employs the true experimental method to design 11 different hybrid (FM-AM-FM) screening combinations in accordance with Kodak/Creo's Maxtone hybrid screening technology. Hybrid screening and CTP technologies were used in flexography to print a specially-designed test form on PVC substrate. Differences in print attributes between PVC substrates printed via the 11 hybrid screening combinations were measured, and statistical analyses were used to identify a combination with an optimal FM-AM-FM tone percentage. It is hoped that the results of this study can help flexography printers to better understand the characteristics of various screening techniques, allowing them to improve printing quality and achieve the highest customer satisfaction. The best hybrid screening combination of FM-AM-FM (highlight-midtone-shadow) found in this study is provided to printers as a reference enabling them to improve production effectiveness and quality, while reducing printing costs and waste, enabling the quality of flexography in Taiwan to progress.

Keywords: AM screening, flexography, FM screening, hybrid screening, print attributes

Miha Lazar, Aleš Hladnik

Faculty of Natural Sciences and Engineering, University of Ljubljana
Snežniška 5, SI-1000 Ljubljana
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Abstract
Segmentation of a digital image whose histogram does not allow for clear and easy differentiation between the features of interest and the background pixels, requires the use of an advanced thresholding algorithm. In our study two local, i.e. adaptive, thresholding procedures with various sizes of small picture regions (windows) were implemented on an image of a lab handsheet made of repulped coloured prints in order to accurately identify the location and the number of residual toner particles. One of the applied algorithms was based on the information maximization of the thresholded image while the other was a modified Niblack's method. Results of the study suggest that the latter method outperforms the former one when using a large window size. Information maximization algorithm typically fails to detect some lighter and coloured areas of objects of interest.

Keywords: Algorithms, image binarization, image processing, local thresholding