Optimal〝n〞Values for Yule-Nielsen Equation to Measure Dot Areas on Compact Discs

Author: Yung-Cheng Hsieh(Graduate School of Applied Media Arts of National Taiwan University of Arts)

Vol.&No.：Vol. 46, No. 1&2
Date：October 2001
Pages：29-50
DOI：10.6301/JNTNU.2001.46.04

Abstract：

In this information age, compact disc decorating has become an area of extreme interest for printers due to the increasing need of the digital market. One of the most exciting developments in compact disc printing over the past two years has been the use of UV waterless offset printing. The main consideration of adopting UV waterless offset decorating is for "magazine" quality. Recently, CD printers put much emphasis on dot area measurements in order to monitor and assess their dot reproduction quality. Fortunately, there is a growing range of densitometers that can accurately check the output of almost all media from film and plate, to conventional litho and digitally printed matter. For most densitometers, Murray-Davies (MD) and Yule-Nielsen (YN) are the two equations used to compute the halftone dot areas of printed matters. Many literatures agree with that YN equation with an optimal n factor is a better method to measure printed dot areas, but the question is "what the optimal n factor should be?" The purpose of the study was to find out the optimal n-factor value (range) for the compact discs printed using the waterless offset process. The original contains 32 patches from 25% to 56% tints. One hundred CDs were printed and 50 of them were systematically randomly selected for analyses. An expert observer was carefully selected to identify the true 50% tint, and then, the true 50% tint was captured by a specially-purchased optical image capture system (OICS) in combination with WIPLab and Photoshop software to analyze and compute dot areas for the CDs. A X-Rite 530 spectrodensitometer was used to read the sampled CDs using 10 different n-factor values ranged from 1.1 to 2.0. Finally, the correlation analyses were performed to investigate the correlation between the OICS_WIPLab and densitometric readings, and the correlation between the OICS_Photoshop and densitometric readings. The major findings are as followings. (1) Based on the OICS_WIPLab analysis, the best n-factor value for densitometers is 1.16 and its optimal range is 1.11 ~ 1.16. (2) Based on the OICS_Photoshop analysis, the best n-factor value for densitometers is 1.12 and its optimal range is also 1.11 ~ 1.16. (3) Photoshop is a commonly used image processing software in the printing industry, whereas, WIPLab is a specially purchased image analysis software in this study, which is originally developed by the biochemical industry. Both are reliable software to analyze irregular shape areas. However, this study shows that Photoshop is a better method to compute irregular printed dot areas on CDs in terms of the consistency and accuracy of measurement.

Keywords：compact disc decorating, dot areas, "n" factor, Yule-Nielsen equation, waterless offset printing

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