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ABSTRACT LIN, JUAN. Factors Affecting the Perception and Measurement of Optically Brightened White Textiles. (Under the Directio

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ABSTRACT LIN, JUAN. Factors Affecting the Perception and Measurement of Optically Brightened White Textiles. (Under the direction of Prof. Renzo Shamey). Whites comprise approximately 3% of the total volume of CIELAB color space, but their relative importance is much larger than the small volume of the color solid that they occupy. Textile products commonly contain many different textures and patterns. Variations in surface roughness can significantly affect the colorimetric attributes of textile substrates. In addition to texture, other influential factors include background color, luminance in the viewing field, physical size of samples, and sample presentation mode. Moreover, surface texture's effect on the perception and measurement of white substrates, including those containing fluorescent brightening agents (FBAs) is not fully understood. It is well established that surface roughness influences color perception. A number of recommended color difference formulae, e.g., CMC (l:c), CIE94 and CIEDE2000, include adjustment factors to account for varying interaction of light with different surfaces. More than 100 whiteness indices were also developed. Main factors influencing these equations include: 1. the visual experimental data developed; 2. accuracy and precision of the spectrophotometers used in measurement of optically brightened materials; 3. accuracy of the correlation model between measured and visual data; and 4. the uniformity of the SPD of the light sources used for visual assessments in viewing booths. A number of studies have reported unsatisfactory correlations between visual responses and CIE whiteness models especially for tinted white samples. The unsatisfactory performance is not solely due to errors in the formula, but may be due to one or more critical variables that currently are not adequately controlled. These variables include: 1. Differences in geometry and light sources between spectrophotometers used for measurement of fluorescent materials; 2. Unknown or non-standardized UV emission of lamps used in standard viewing booths. The objective of this research is to investigate several factors affecting the perception and measurement of optically brightened white textiles with a view to determine whether the performance of the whiteness index can be improved. Several approaches were examined to achieve this objective: 1. Preparation of textile sample sets with various textures to be used in visual and instrumental evaluation of whiteness; 2. Visual/instrumental evaluation of the effect of texture on lightness and whiteness under sources simulating illuminant D65; 3. Visual/instrumental evaluation of the effect of texture on perceived whiteness under sources simulating illuminant D75; 4. Visual/instrumental evaluation of the effect of texture on perceived whiteness under light source/illuminant A and source U30; 5. Examination of the role of UV content in viewing booths simulating illuminants D65 and D75 and determination of the effect of UV on visual assessment and instrumental measurement of fluorescent white samples; 6. Assessment of the uniformity of a monitor and examination of the uniformity boundary of the screen for display of white textile samples; 7. Development of software incorporating color management system to generate a patch incorporating simulated textures; 8. Generating images of the textured substrates with similar lightness and whiteness properties using linear transformation methods; 9. Designing a visual assessment protocol to evaluate perceived whiteness, conduct visual assessment using reference anchors based on forced ranking method; 10. Examination of the effect of background on perception of simulated white textiles on the monitor; 11. Analysis of the whiteness perception results based on texture variation; 12. Correlation of responses from perceived whiteness of knitted textures to perceived whiteness of simulated textures; and 13. Modification and examination of the whiteness index by incorporating the effect of texture. © Copyright 2013 by Juan Lin All Rights Reserved Factors Affecting the Perception and Measurement of Optically Brightened White Textiles by Juan Lin A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Fiber and Polymer Science Raleigh, North Carolina 2013 APPROVED BY: _______________________________ ______________________________ Dr. Renzo Shamey Dr. David Hinks Committee Chair ________________________________ ________________________________ Dr. Henry Joel Trussell Dr. Douglas Gillan DEDICATION To my whole family, my mother, father and sister, for without their help and support, graduate school would have been surely impossible. To my boyfriend, who has been accompanying and helping me throughout this long journey. ii BIOGRAPHY Juan Lin grew up in Shanghai, China. She finished her undergraduate studies at the Information Engineering University, China, in 2006 and then received an MS in image processing in 2009. Her main research interests include color science, image processing, color measurement and color management. iii ACKNOWLEDGMENTS The author would like to thank Prof. Renzo Shamey, for his advice, support, patience, guidance and financial support throughout this research; and Prof. Joel Trussell, member of the advisory committee, for his great contribution to the author's development of image processing skills. Their continuous input and encouragement provided immeasurable support for the author. Also, the author would like to extend her gratitude to Prof. David Hinks and Prof. Douglas Gillan, members of the advisory committee, for their valuable suggestions and encouragement. In addition, the author thanks all observers who willingly participated in the visual assessments related to this work. The author is very grateful to Mr. Jeff Krauss for the help received in bleaching and brightening fabric samples and Mr. Brian Davis for the help in setting up the machinery which enabled the author to prepare knitted samples with various textures. Thanks are also due to Dr. Yuzheng Lu and Mr. Renbo Cao, for their help and suggestions during experiments. Finally, the author would like to thank Ms. Wenwen Zhang, Mr. Nanshan Zhang, Ms. Ting He and Mr. Xiaofeng Qin for their continued love, support, help and encouragement throughout this study. iv TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................................. xiii LIST OF TABLES ............................................................................................................................. xxii TERMS AND NOMENCLATURE ................................................................................................. xxvii I. Introduction ......................................................................................................................................... 1 II. Literature Review .............................................................................................................................. 2 1. Color Vision and Factors Affecting Color Perception ....................................................................... 2 1.1 Perception of Color....................................................................................................................... 2 1.1.1 Structure of the Eye ............................................................................................................... 2 1.1.2 Theories of Color Vision ....................................................................................................... 8 1.1.2.1 Trichromatic Theory ........................................................................................................... 8 1.1.2.2 Opponent Color Vision Theory .......................................................................................... 9 1.1.2.3 Zone Theory ..................................................................................................................... 11 1.1.3 Color Constancy .................................................................................................................. 13 1.1.3.1 Color Contrast .................................................................................................................. 14 1.1.3.2 Lightness Crispening ........................................................................................................ 20 1.2 White and Whiteness .................................................................................................................. 21 1.3 Illuminants and Light Sources .................................................................................................... 27 1.3.1 Color Temperature ............................................................................................................... 29 v 1.3.2 Light Sources ....................................................................................................................... 31 1.3.3 CIE Standard Illuminants .................................................................................................... 33 1.3.4 Fluorescent Lamps and Tubes ............................................................................................. 37 1.3.5 LEDs .................................................................................................................................... 39 1.4 Texture Analysis ........................................................................................................................
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