Rochester Institute of Technology RIT Scholar Works Theses 4-1-1991 An Analytical model for the colorimetric characterization of color CRTs Ricardo J. Motta Follow this and additional works at: https://scholarworks.rit.edu/theses Recommended Citation Motta, Ricardo J., "An Analytical model for the colorimetric characterization of color CRTs" (1991). Thesis. Rochester Institute of Technology. Accessed from This Thesis is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. An Analytical Model for the Colorimetric Characterization of Color CRTs by Ricardo J. Motta A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Degree in the Center for Imaging Science in the College of Graphic Arts and Photography of the Rochester Institute of Technology April 1991 Signature of the Author ~ _ Ricardo J. Motta Accepted by _.:..:.M:..:e:..:.,:h:..=d.:...iV.:....:a:.:e:..:;z....:.-I.:..;ra~v.::.an:...:.;i:..- _ Coordinator, M.S. Degree Program College of Graphic Arts and Photography Rochester Institute of Technology Rochester, New York CERTIFICATE OF APPROVAL M.S. DEGREE THESIS The M.S. Degree Thesis of Ricardo J. Motta has been examined and approved by the thesis committee as satisfactory for the thesis requirement for the Master of Science Degree Dr. Roy S. Berns, Thesis Advisor Ms. Paula Alessi Mr. Leroy DeMarsh 11 IIIII(III~ III~ IIIIII~III~~ II111 (IIII~II ~IIII~IIIIIIIIII RDDD6D4D867 THESIS RELEASE PERMISSION FORM Rochester Institute of Technology College of Graphic Arts and Photography Title of Thesis: An Analytical Model for the Colorimetric Characterization of Color CRTs I, Ricardo J. Motta, hereby grant permission to the Wallace Memorial Library of R. 1. T. to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit. Date: ill An Analytical Model for the Colorimetric Characterization of Color CRTs by Ricardo J. Motta A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Degree in the Center for Imaging Science in the College of Graphic Arts and Photography of the Rochester Institute of Technology Abstract To be a viable instrument for color appearance research, the color Cathode Ray Tube has to be very well calibrated and characterized. The purpose of this research was to develop the techniques and methods used to carry out such characterization, and also to evaluate to what degree of precision and accuracy can such a characterization be performed. A new model for predicting the CRT behavior is presented along with the experimental results that validate it. IV Acknowledgements I wish to express my gratitude to a number of individuals and institutions that made this work possible. Dr. Roy Berns has guided me with a generous and firm hand. Through his enthusiasm and his teachings I have learned the fundamentals of color science and found myself engaged in this field. I also want to thank my board of advisors, Leroy DeMarsh and Paula Alessi, for their good advise and patience. Their suggestions and support were crucial for the success of this work. At the Center for Imaging Science I have found generous help and friendship. I especially wish to thank Tim Gallagher and Dick Norman for technical support, and Peter Engeldrum, Mark Fairchild, Mark Gorzynski and Dennis Daoust for the many long and enlighting conversations. I have especially fond memories of the late Dr. Ronald Francis. His guidance and example through my early years at CIS had a lasting impact on my character and intellectual horizons. The Xerox Corporation has provided me with help in the form of a stipend and equip ment. This crucial help is sincerely appreciated. Key contributions in form of equipment Photo- and good advise were also provided by the Eastman Kodak Co., Minolta Corp., the Research division of Kollmorgen Corp., and Tektronix Corp. I also want to gratefully acknowledge the Brazilian Government for a two year scholarship (CNPq.202070.84). Finally, I wish to thank my parents. It was through their love and generosity that I found the means to grow. Para Marcia, com amor. g^A^b\>*^- finish it?" "Finish it? Why would I want to Contents 1 INTRODUCTION 1 1.1 Research Objectives 7 2 THEORETICAL MODEL 10 2.1 Introduction 10 2.1.1 A Simple Model 12 2.1.2 Failures of the Simple Model 12 2.2 Predicting the CRT RGB Tristimulus Values 14 2.2.1 Digital Image Data 16 2.2.2 Look-Up-Table 16 2.2.3 Video Generator 17 2.2.4 Video Amplifier 18 2.2.5 Electron Gun . 18 2.2.6 Phosphors . 19 2.2.7 Screen Radiance 20 2.2.8 Ambient Light 21 2.2.9 Total Radiance 22 2.2.10 CRT Tristimulus Values 22 2.2.11 Normalizing the Transfer Function Equation 23 2.3 A Model for CRT Calibration 25 2.3.1 Evaluating Gamma 26 vii Vlll 2.3.2 Simplified Transfer Function Model 29 3 THE CALIBRATION OF A CRT 31 3.1 Characterization Method 31 3.1.1 Permanent Characteristics 32 CRT stability and latency time 32 Phosphor constancy 32 Gonio properties 33 Phosphor Chromaticities 33 3.1.2 Transitory characteristics 34 Setup 34 Viewing conditions 35 Screen uniformity 36 Load dependency 36 Transfer function and White point 36 3.2 Characterizing the Transfer Functions 37 3.2.1 Setup 37 3.2.2 Algorithm 38 3.2.3 Results 39 3.3 Estimating the Model Parameters 40 3.3.1 A Nonlinear Algorithm 40 3.3.2 Results 42 3.4 Verifying the Model 43 4 CONCLUSIONS 47 4.1 Recommendations 49 A DERIVATION 52 A.l Computer Image Formation 52 A.1.1 Digital Images 52 IX A.1.2 The LUT 55 A.1.3 The Video Generator 58 A.l.3.1 The RS-170 Signal 58 A.l.3.2 The Frame Rate 60 A.l.3.3 Voltage Levels 64 A.l.3.4 The Effect of the Modulation Transfer Function 66 A.1.4 The Video Equation 70 A.2 The Cathode Ray Tube Display 71 A.2.1 The Video Amplifier 73 A.2.2 The Cathode Ray Tube 75 A.2.3 The Electron Gun 78 A.2.4 Phosphor Screen 83 A.2.5 The Energy Conversion 84 A.2.6 Phosphor Efficiency 86 A.2.7 Deviations from Linearity 88 A.2.8 Phosphor Decay and Dwell Time 90 A.2.9 Flicker 94 A.2. 10 Composition of the Phosphors 96 A.2. 11 Screen Radiance 98 A.2.12 Phosphor Constancy 102 A.2.13 RGB CRT Tristimulus Values 104 A.3 The CRT Color 105 A.3.1 CRT Color Mosaic 106 A.3.1.1 Hexagonal array, circular phosphor dots 110 A.3.1.2 Linear array, striped phosphors Ill A.3.1.3 Hexagonal array, rectangular phosphor dots Ill A.3.2 Additive Color Synthesis 112 x B Experimental Techniques 122 B.l Introduction 122 B.2 Apparatus 123 B.2.1 Location 123 B.2.2 Computers 124 B.2.3 Software 124 B.2.4 Video Generator 124 B.2.5 CRTs 124 B.2.6 Detectors 125 B.2.7 Measurement Instruments 126 B.3 Procedures 126 B.3.1 CRT Areas 126 B.3.2 Data Collection 127 B.3.2.1 PR703A/PC 127 B.3.2.2 TV-2160 128 B.3.3 Placement of the TV-2160 Probe 129 C Tristimulus Measurements 130 C.l Introduction 130 C.l.l Precision 130 C.1.2 Accuracy 131 C.2 Repeatability 132 C.3 Integration Time, Area and Noise 132 C.3.1 Detection of single emissions 135 C.3.2 Integration of several emissions 137 C.3.2.1 Integration of noise 137 C.3.2.2 Synchronization of measurement 138 C.4 Minolta Repeatability 140 C.4.1 Experimental 141 XI C.4.2 Results 142 C.5 CRT Repeatability 144 C.5.1 Introduction 144 C.5.2 Long term stability 145 C.5.3 Short term repeatability 146 C.5.3.1 Experimental 146 C.5.4 Results 147 D Minolta Linearity Correction 151 D.l Photometric Scale 151 D.l.l Inverse Square Law 153 D.1.2 Experimental 155 D.1.3 Results 156 E Load Dependency 161 E.l Introduction 161 E.2 Additivity Failure 163 E.2.1 Measuring the additivity failure 164 E.2.1.1 Additivity of the phosphor screen 166 E.2. 1.2 Measuring vq\ 167 E.2.2 Modeling the Additivity Failure 169 E.3 Accounting for the Deviations 171 F Goniocolorimetric Properties 174 F.l Introduction 174 F.2 Experimental 177 F.3 Results 184 F.4 Conclusions 186 G Screen Uniformity 190 Xll G.l Introduction 190 G.2 Qualitative view 196 G.2.1 Experimental 196 G.2.2 Results 196 G.3 Quantitative view 201 G.3.1 Experimental ; 201 G.3.2 Estimating variance 202 G.3.3 Results 205 G.4 Discussion 208 H Uniformity Measurements 212 I Tables of Goniocolorimetric Properties 219 J Program crtCAL.c 224 K Program crtCALC.c 226 List of Figures 1.1 Typical 25 kV, 90o shadow mask color cathode ray tube 2 colorimeter" 1.2 Schematic of Robertson's "future visual 3 1.3 Diagram of CRT based color psychophysics laboratory at MCSL 8 2.1 Transfer function of a computer driven CRT monitor 11 2.2 The 7 obtained by a simple model is not always the same over the entire range of radiances 13 2.3 Block diagram of the CRT image formation process 15 2.4 Estimating gamma for fixed gain a and different offsets b 27 2.5 Estimating gamma for fixed offsets b and different gains a 28 3.1 Histogram of CRT model AE*b errors over entire CRT gamut 44 3.2 Histogram of AE*b color difference due to errors of 1 digital count 45 3.3 AE*b model errors for only the red and green channels 46 A.l Block diagram of the Number 9 512x32 graphics board 54 A.2 A LUT where 4 bits are mapped to 24 bits 56 A.3 Different features of the RS- 170 video signal 59 A.4 Interlaced path of scanning electron beam 61 A.5 Typical synchronization pulses 62 RS- A.6 Blanking and display periods of the 170 video signal 65 xiu XIV A.7 Downward and upward paths of the electron beam when scanning and inter laced image 66 A.8 Voltage values of a single line of the RS- 170 signal 67 A.9 Typical CRT circuit 72 A.