色外貌模式在彩色包裝印刷應用之研究

在彩色包裝印刷業常發生一種現象，當客戶的企業識別色分別印刷於不同相對背景亮度上，利用分光光譜儀所測量色塊顯示的色差非常小，但人眼所接受到的刺激差異量確是非常大，造成業者與客戶間產生糾紛，為進一步解決此問題，所以有必要針對此一問題進行深入探討。所以，當跨不同觀測環境／條件時，就必須應用色外貌模式，以求出另一觀測環境下色彩的外貌屬性，也就是求得所謂的“對等色”﹝Corresponding color，或稱為“對應色”﹞〉－亦即是在找出在某相對背景亮度Y(下标 b)下觀測與另一個相對背景亮度Y(下标 b)觀測經過人眼適應後所產生對於人眼視覺觀測上會有相同的視覺感受的顏色。本研究乃利用CIECAM02色外貌模式進行模擬對等色實驗並進行分析比較，在無彩度相對背景亮度改變下，對不同色相色彩或不同明度色彩是否產生不同差異，因此在色塊色外貌變化評估方面，試著改變相對背景亮度Y(下标 b)，並固定環境光照度、光源色溫等以利實驗進行，探討相對背景亮度Y(下标 b)對色塊色外貌的影響，分析在CIECAM02模式中，將多項人眼知覺屬性參數的設定下，進而描述對等色的情況，透過標準sRGB顯示器進行模擬表現，同時進行心理物理實驗驗證CIECAM02模式所推導出的色彩要素：明度(Lightness)、彩度(Chroma)及色相(Hue)的評估結果是否可以穩合，也就是驗證CIECAM02是否可以直接應用彩色包裝印刷上，解決在無彩度相對背景亮度對企業識別色的色外貌變化情況。

關鍵字

相對背景亮度Y(下标 b) ； CIECAM02 ；色外貌模式；包裝印刷；對等色； CIECAM02 ； sRGB

並列摘要

Often It happens in package printing industry that the same spot colors, printed against different backgrounds (including various relative luminances, background-colors) visually mismatch to each other. Therefore it is needed to have a better solution than only just colorimetrically using measuring instruments such as spectro-colorimeters/spectrophotometers to decide the acceptability standards or quantization data. In this research, as considered in the application of package printing, the CIECAM02 color appearance model was used to approximate corresponding colors, for different hue angles and lightness, among various relative luminaces of gray backgrounds (i.e. Yb values).. A set of psychophysical experiments, using a paired-comparison method, was conducted to evaluate the performance of CIECAM02 model. An sRGB format of LCD was used as a soft-proof for displaying those simulated images/colors tested. Simultaneously, observers were instructed to respectively adjust three color bars of RGB channels to produce every corresponding color under a test background which would match the color appearance of its corresponding reference color under the reference viewing condition/ gray-background considered for each color.