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Assessing Colour Differences of Lighting Stimuli Using a Visual Display Maria Georgoula Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Design November, 2015 - 2 - The candidate confirms that the work submitted is his/her own, except where work which has formed part of jointly authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Parts of this thesis have been published at the CIE 2016 conference paper entitled “Specification for the Chromaticity of White and Coloured Light Sources” authored by Georgoula Maria, Cui Guihua, Pointer R Michael, and Luo M Ronnier. Summary of the experimental procedure from Chapter 3, notable ellipse parameters from Chapter 4, and average performance of colour difference metrics from Chapter 6 were included in the paper. The author, Maria Georgoula, collected all the data, conducted data analysis and wrote the paper. Guihua Cui assisted with the data analysis by providing advice and checking the results. Michael Pointer provided comments and proof reading of the paper. Ronnier Luo defined the initial structure and reviewed the paper. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Maria Georgoula to be identified as Author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988. © 2015 The University of Leeds and Maria Georgoula - 3 - Acknowledgements This research has been carried out under the direction and supervision of Professor M. Ronnier Luo and Dr. Vien Cheung; to whom I am most grateful for their tireless support and guidance throughout my studies. Special acknowledgements are given to the State Scholarships Foundation of Greece (IKY), which sponsored the first years of my Ph.D. studies in the University of Leeds. This work would not have been possible without the support of the Foundation. Moreover, I would like to give special thanks to Dr. Guihua Cui, Dr. Peter Rhodes, Dr. R. Michael Pointer and Dr. Phil Green for the discussions and assistance whenever the opportunity arose. I would also like to thank Professor Bryan Rigg and Professor Stephen Westland for their expert advice in support of improving my thesis, and the great discussions through the viva examination. Many thanks due to every observer for voluntarily participating at the psychophysical experiments, and every other colleague for their assistance in so many ways. Last but not least, I am indebted and thankful to my friends and family for their wonderful encouragement, support and understanding. I am blessed to have you in my life. - 4 - Abstract A large scale experiment was carried out to accumulate colour difference discrimination data for lighting stimuli which were simulated on a display. Twenty six colour centres were selected and twenty one pairs of chromaticity difference were prepared surrounding each colour centre. Each pair was assessed using ratio method against a grey and a black background by a group of 20 normal colour vision observers. Both white and coloured lighting stimuli were used; corresponding to specifications for the solid state white lighting products and part of the MacAdam colour centres respectively. The latter defined the fundamental research for visual sensitivities known as just noticeable difference (JND). The results were used to test colour spaces and chromaticity diagrams as well as to evaluate colour difference predictions of various colour difference formulae and colour appearance models. It was found that u'v' chromaticity diagram can represent colour discrimination data for lighting colour stimuli more uniformly. Moreover, CIELUV colour difference formula performed better in predicting colour differences for lighting stimuli; especially when using black background. It performed better than CIEDE2000 and CAM02- UCS formulae, which were derived based on surface colours, even though it has been shown in the previous studies that these perform well when simulating surface colours on display. These points also support that the experimental arrangement could potentially be used to simulate light sources (luminaires) in order to evaluate them as lighting stimuli. Furthermore, the visual results obtained against the black background can mostly be predicted better by the models than those against the grey background for lightning stimuli. - 5 - Table of Contents Acknowledgements ..................................................................................... 3 Abstract ........................................................................................................ 4 Table of Contents ........................................................................................ 5 List of Tables ............................................................................................... 9 List of Figures ........................................................................................... 11 List of Equations ....................................................................................... 15 Chapter 1. Introduction ....................................................................... 17 1.1. Background ................................................................................. 17 1.2. Aims of Thesis ............................................................................. 17 1.3. Thesis Overview .......................................................................... 19 Chapter 2. Literature Review .............................................................. 21 2.1. Colour Fundamentals .................................................................. 21 2.1.1. CIE Colorimetry ........................................................... 22 2.1.1.1. Standard Illuminants and Sources ....................... 22 2.1.1.2. Standards of Reflectance ..................................... 23 2.1.1.3. Geometric Conditions .......................................... 24 2.1.1.4. Standard Colorimetric Observers ......................... 25 2.1.1.5. Tristimulus Values and Chromaticity Coordinates ................................................................. 25 2.1.1.6. Luminance Factor ................................................ 27 2.1.1.7. Uniform Colour Spaces ........................................ 27 2.1.2. Colour Difference Formulae ........................................ 28 2.1.2.1. CIELAB and CIELUV Formulae ........................... 28 2.1.2.2. CIEDE2000 Formula ............................................ 30 2.1.3. Colour Difference Datasets ......................................... 31 2.1.4. Colour Appearance Overview ..................................... 34 2.1.4.1. Viewing Field ........................................................ 34 2.1.4.2. Colour Appearance Attributes .............................. 35 2.1.4.3. Colour Appearance Phenomena .......................... 36 2.1.4.4. Parametric Effects ................................................ 38 2.1.5. Colour Appearance Models ......................................... 39 2.1.5.1. CIECAM02 Model ................................................ 40 - 6 - 2.1.5.2. CAM02-SCD, CAM02-LCD and CAM02-UCS Colour Spaces............................................................. 43 2.2. Colour Management .................................................................... 45 2.2.1. Colour Management Overview .................................... 45 2.2.2. Colour Management Steps ......................................... 47 2.2.3. Colour Management Paradigms.................................. 50 2.2.4. Device Characterisation .............................................. 50 2.2.4.1. Display Characterisation ...................................... 51 2.3. Visual Psychophysics .................................................................. 53 2.3.1. Introduction to Psychophysics ..................................... 53 2.3.2. Psychophysical Methods ............................................. 55 2.3.2.1. Ratio Scaling ........................................................ 55 2.4. Colour Discrimination Ellipses ..................................................... 57 2.4.1. Geometrical Properties of Ellipses .............................. 57 2.4.2. The MacAdam Experiments on Visual Sensitivities .... 58 2.4.3. Parameters of Ellipses ................................................ 61 2.4.4. Aperture Mode Studies on the Precision of Colour Matching ............................................................................. 62 2.4.5. Fitting of Ellipses ......................................................... 63 2.5. Lighting Standards ...................................................................... 65 2.6. Statistical Methods and Measures of Fit ..................................... 67 2.6.1. General Statistics ........................................................ 67 2.6.2. Standardized Residual Sum of Squares (STRESS) .... 68 2.6.3. Colour Uncertainties .................................................... 70 2.7. Conclusion .................................................................................. 71 Chapter 3. Experimental ...................................................................... 72 3.1. Measuring Instrumentation
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