應用Yule-Nielsen公式測量光碟網點面積之適當「n」參數值－－以無水平版為版式，UV油墨為印墨

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

身處二十一世紀的資訊時代，光碟已成為日常生活中普遍且不可或缺的用品，美國市場調查公司IRD之報告指出，光碟將有極快速之市場成長，其中，軟體、影音等光碟產品通常以開發全球市場為主，國內光碟印刷廠商若能提升品質，不僅可獲得國內市場的支持，更能進一步拓展國際市場。在印刷品質控制的過程中，網點面積之測量是不可或缺的一項重要作業。使用濃度計測量網點面積時，設定適當之〝n〞參數值十分重要，帶入適當〝n〞參數值之Yule-Nielsen公式在網點面積測量上較Murray-Davies公式更為有效且準確。因此，本研究主要目的在找出應用Yule-Nielsen公式測量無水平版光碟印刷表面之網點面積時適當之〝n〞參數值，期望經由實驗驗證所估計出來的「n參數值」能作為業者在控制或提升光碟印刷品品質之參考依據。本研究以實驗為方法，在原稿上設計25%到56%網點共32個階調，以此原稿印製100片的光碟，經系統隨機抽樣方式抽取50片樣本。將50片樣本交由專家觀測者，使用印刷專用放大鏡（loupe）以肉眼判斷方式來界定此原稿之專家認為的真正50%網點，接著使用光學影像擷取系統（Optical Image Capture System, OICS）來擷取專家所建議之真正50%網點的影像，並採用WIPLab軟體和Photoshop影像處理軟體來計算網點面積，該網點面積值即作為相關性分析時之標準對照值。本研究並使用X-Rite530分光密度儀，設定10個不同的〝n〞參數值（範圍介於1.1~2.0之間），將測得之網點面積輸入統計軟體以進行分析，本研究之重要結果如下：1.以WIPLab軟體計算50%網點面積所建議之最佳「n參數值」為1.16，最佳n值範圍介於1.11~1.16之間。2.以Photoshop軟體計算50%網點面積所建議之最佳「n參數值」則為1.12，最佳n值範圍亦介於1.11~1.16之間。3.WIPLab為真實色彩影像處理與分析之軟體，應用於醫學影像、生化分析、工業檢視等方面；Photoshop軟體則為專門應用在印刷影像處理之軟體，兩種套裝軟體均可分析不規則影像之面積。本研究顯示，Photoshop軟體在光碟印刷上網點面積之分析可得較精確且穩定的結果。

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.