Abstract
本研究的目的是在近似均勻的色彩空間中，探討目標物與背景間色彩對比與人眼視覺清晰度之關係，並根據此關係來建立色彩對比之尺標。視覺清晰度定義為 50 % 恰可辨識率所導致的最小可分辨視角，而色彩對比是用恰可分辨差異的倍數來度量兩顏色間之差異程度，而在近似均勻的色彩空間中，兩顏色座標間之距離與恰可分辨差異的數目成相當一致的線性關係，可作為色彩對比量化的依據。在所有的色彩空間中，我們選用均勻度與實用性都廣為肯定的 CIELAB 及 OSA 兩色彩空間作為本研究的基礎空間，在這兩空間中，分別探討色彩對比對視覺清晰度之影響。本論文共分為五章。第一章陳述本研究的背景、動機、以及目的。第二章則探討一些關於色彩對比與視覺清晰度的背景原理與相關文獻。第三章與第四章是本論文之重點，分別以 CIELAB 及 OSA 兩色彩空間來構建色彩對比之尺標。第五章則將這兩個研究之結果加以總結，並對未來之研究提出建議。在第三章裡，我們採用彩色絹印的藍多爾圈視力檢查表來量測受試者之最小可分辨視角。研究結果發現，最小可分辨視角與色彩對比成指數反比的關係。然而，大變異量顯示 CIELAB 1976 色差公式對於估計色彩對比仍有不適之處。而在逐步調高明度對比之係數為 2.75 倍後，新的色彩空間顯示能構建出一套更符合人眼主觀感覺的色彩對比尺標。第四章則用相同的方法的方法在 OSA 色彩空間中構建色彩對比尺標。其研究結果顯示，最小可分辨視角與色彩對比成一指數反比關係，而且明度對比對視覺清晰度之影響要比色度對比要大。實驗結果也顯示，明度對比與色度對比間具有加成性的交互作用。根據這些結果，我們證實 OSA色彩空間及其色差公式確能精確地將色彩量化，並進而估算彩色印刷文字或標誌的尺寸。The purpose of the study is to investigate the relationshipbetween visual acuity and color contrast, and use thisrelationship to construct a color contrast scale. Visual acuityis characterized by 50% minimal separable visual angle usingLandolt-C. The color contrast is characterized by the distancebetween two colors in approximate unifrom color space. Thedissertation of this study is presented as five chapters.Chapter 1 states the backgrounds, motivation, and objectives ofthis research. Chapter 2 describes some related backgroundknowledge in color contrast and visual acuity, and reviews somerelated studies. Chapter 3 and 4 which are the major parts ofthis study are presented as two independent papers. These twopapers using different color spaces, CIELAB and OSA, toconstruct color scales based on visual acuity. In the lastchapter, Chapter 5, some results of these two papers aresummarized and some recommendations for future study are given.Chapter 3 reports the relationship between CIELAB colorcontrast and human visual acuity. In this study, anexperimental measure of visual acuity is made under 342 colorLandolt-C test sheets. The results shows that minimal separablevisual angle (MSVA) is inverse log-linear with CIELAB colorcontrast. However, the great variance reveals that CIELAB colorspace remains fallacious in evaluating the relationship betweenVA and color contrast. By stepwisely raising coefficient ofluminance contrast in CIELAB difference formula up to 2.75, thenew color space appears to be more suitable for constructing acolor contrast scale that human perceived. Chapter 4 uses thesame experimental method based on OSA color space. The resultsshow that MSVA is inverse log-linearly related to OSA colorcontrast, and luminance contrast is more salient than chromaticcontrast. There is also evidence of an additive interactionbetween chromatic contrast and luminance contrast.