利用同色異譜開發白光LED色彩品質檢測導具

Development of Color Quality Inspection Guide for White-light LED Based on Metamerism

油墨配方和光源是影響印刷色彩表現的重要兩項因素，目前已發展出基於多色網點面積率的數學模型來預測油墨配方的色彩再現性，例如，諾克伯光譜模型為基於原色油墨的光譜反射率及其網點面積率建立的半色調印刷色彩預測模型，但僅以簡單的線性方程式來描述原色光譜反射率及網點面積率之間的關係是不夠精確的。另外，印刷工業使用的推薦標準光源為色溫5000 K高演色性光源，目前市面上有照明指示貼紙可以用來檢測彩色打樣用光源是否接近CIE標準光源，其設計原理即是利用條件等色性，當照明環境越符合指示貼紙所指示的日光光源時，貼紙上的兩個色塊所呈現的顏色越接近。LED因為其壽命長、節能、高發光效率等等優勢，逐漸取代傳統光源，由於目前作為主流的藍／黃二色型白光LED光譜能量分布與CIE D50日光光源的光譜能量分布差異非常大，導致照明指示貼紙在5000 K白光LED下無法發揮功能。本研究根據上述背景設計了以下三項實驗，分別為：（1）實驗一「優化諾克伯印刷色彩預測模型」，在印刷油墨的控制上，針對諾克伯印刷色彩預測模型進行優化並評估優化後模型的色彩預測能力；（2）實驗二「設計同色異譜對光譜：考量LED與日光」，為利用同色異譜設計照明檢測導具，目的在於區分5000 K白光LED照明與CIE D50日光照明；（3）實驗三「設計同色異譜對光譜：考量高／低演色性LED」，同樣利用同色異譜設計可實際應用於印刷現場的照明檢測導具，目的在於區分高演色性5000 K白光LED低演色性5000 K白光LED照明。實驗一結果顯示，優化後的色彩預測模型以修正網點面積率與諾克伯光譜模型的預測色彩能力最佳。實驗二成功產生「在5000K白光LED下無色差，在標準D50環境下有色差」同色異譜對之光譜反射率。實驗三結果成功產生「在低演色性白光LED下無色差，在高演色性白光LED下有色差」及「在高演色性白光LED下無色差，在低演色性白光LED下有色差」同色異譜對之光譜反射率。本研究提出之光譜預測法及篩選條件，可有效模擬在指定白光LED光源下達到等色之同色異譜對。

Printing ink and illumination are two important factors that affect color appearances of printing media. Color prediction model is one of the attractive researches in the field of printing color reproduction for a long time. Several mathematical models have been developed to predict color performances of halftone colors, such as the spectral Neugebauer model, which was developed for predicting printing color based on the reflectance spectra and dot area of the Neugebauer primary colors. The basic spectral Neugubauer model which described the relationship between CMY ink amounts and reflection spectra using a linear equation was completely inaccurate. In addition, Metamerism is a phenomenon that two objects or colors with different spectra show similar colors under a particular light source, while showing different colors under the other sources. There are several types of paper-based lighting indicators which make use of metamerism property are released for detecting standard illuminants currently. However, it has been found that the D50 lighting indicator cannot work well for general white-light LEDs. Based on the above motivation, this study designed three experiments as follows: (1) Experiment 1 named ''Optimized the Neugebauer color prediction model'' is designed to optimize the CMY dot areas, several Neugebauer-based color prediction models were assessed; (2) Experiment 2 named ''Spectral design of metamer in terms of LED and daylight''. It designed a novel color quality inspection guide for distinguishing between white-light LED and CIE daylight based on metamerism; (3) Experiment 3 named ''Spectral design of metamer in terms of high and low color rendering index (CRI) LEDs''. It designed a novel color quality inspection guide for distinguishing between the white-light LED with low CRI and the white-light LED with high CRI. In Experiment 1, the optimized m-DSN model with the best ability to predict printing colors was confirmed. In Experiment 2, we successfully developed the metameric color pairs which have the capabilities of showing similar color under 5000 K white-light LED. In Experiment 3, we also successfully developed two kinds of metameric color pairs, one pair have the capability of showing similar color under white-light LED with low CRI, while showing different colors under white-light LED with high CRI. The other pair has the capability of showing similar color under white-light LED with high CRI, while showing different colors under white-light LED with low CRI. Consequently, the experimental results showed that the proposed spectrum prediction method can effectively simulate the metameric pairs under a specified light source.