How Modern Displays Push Conventional Colorimetry to Its Limit

1. How Modern Displays Push Conventional Colorimetry to Its Limit Abhijit Sarkar*,**, Laurent Blondé*, Patrick Le Callet**, Florent Autrusseau**, Patrick Morvan*, Jürgen Stauder* *Technicolor Research & Innovation , France **IRRCCyN-IVC, University of Nantes, France CREATE 2010, Gjøvik, Norway June 8, 2010

2. About Me… • B.E. Electrical Engineering, Jadavpur University, India, ‘00 • M.S. Architectural Engineering (Lighting), Penn State University, Pennsylvania, ‘05 • MS Color Science, Munsell Color Science Lab, RIT, Rochester, ’08 • Currently: PhD Student at • Technicolor Research & Innovation, Rennes, France (Advisors: Laurent Blondé, Jürgen Stauder) • University of Nantes , France(Advisors:Patrick Le Callet & Florent Autrusseau) • Current Research Topic: • Observer variability issue in modern display colorimetry

3. What is Color? How Do We Measure It? Color is a perception that depends on the response of the human visual system to light, and the interaction of light with objects (also called color stimulus) 0.1547 0.7029 0.1424 Tristimulus Values Spectral Sensitivity of Photoreceptors Spectral Power Distribution

4. Quantitative Representation of Color : Spectral power distribution of a CIE illuminant (e.g. D65) : Spectral reflectance factor of the object : CIE standard observer 2° or 10° color-matching functions Similar for y and z Common representation: xyY

5. In colorimetry, there is a provision for changing the illuminant and the object, but not the observer! Average Observer

6. Observer Metamerism: The color is in your eyes! Two color stimuli with very different spectral power distributions can be a match for one observer and mismatch for the other The more different the spectral power distributions are, the more prominent the effect of metamerism is!

7. Observer Metamerism on a CRT and an LCD: Simulation XYZ (10° SO and D65) M-1CRT/LCD (10°) • dcCRT/LCD(10°) MCRT/LCD (obs2) MCRT/LCD (obs1) • XYZCRT/LCD(obs2) • XYZCRT/LCD(obs1) M-1CRT (obs1) M-1CRT (obs2) • dcCRT/LCD_obs1 • (CRT equiv.) • dcCRT/LCD_obs2 • (CRT equiv.)

8. LCD CRT Obs. 1 (cat. 5) Obs. 2 (cat. 6)

9. LCD CRT Obs. 1 (cat. 5) Obs. 2 (cat. 6)

10. A Color Matching Experiment Using Two Displays • Displays: a narrow-band LCD with LED backlight and a broad-band studio CRT • Observers asked to adjust the color on the left half of the bipartite field (matching field) to match the color on the right half (test field)

11. Preliminary Results from the Color Matching Experiment • Standard observer-predicted color differences (∆E*00) of individual observer color matches found to be significant for some observers

12. Conclusions • In highly color-critical applications using modern displays, employing an average observer model in colorimetry can possibly lead to unacceptable color matches for many color-normal expert observers • Objective of this work: • To develop an observer-dependent color imaging method, where color workflow in a display device can potentially be tuned to one of several observer classes, leading to novel industrial applications

13. Thank you! Acknowledgments • Jean-Jacques Sacré for his help and guidance in preparing the experimental setup • Following colleagues for being the observers in the color matching experiments: • Laurent Blondé • Patrick Morvan • Jürgen Stauder • Arno Schubert • Pascal Bourdon • Séverine Baudry • Emmanuel Jolly • Catherine Serre • Jean-Jacques Sacré

14. Hypotheses: Solution Lies in the Problem Itself… • Color vision of observers can be classified into a small number of categories • A practical experimental setup can be built to classify observers • Color processing in an industrial application can be tuned to one of these categories, leading to a better agreement between real observer perceptions and colorimetry

15. Work-in-Progress: A Novel Experimental Method for Observer Classification Seven Observer Categories (sets of CMFs) + CIE 10° observer Rate categories for many colors: unacceptable, acceptable and satisfactory Determine observer category

16. Observer Categories Through Statistical Analysis of Color-Matching Dataset 4 x- functions 3 y- functions 3 z- functions

17. Results: Observer Classification • For eleven observers, the CIE 10° standard observer (category 1) was not among the two most preferred categories • For three observers, category 1 was rejected as an unacceptable match for all fifteen test colors

18. Conclusions • In highly color-critical applications using modern displays, employing an average observer model in colorimetry can possibly lead to unacceptable color matches for many color-normal expert observers • Real, color-normal observers can be classified into a small number of categories by means of a practical experimental setup suitable for industrial applications • Objective of this work: • To develop an observer-dependent color imaging method, where color workflow in a display device can potentially be tuned to one of several observer classes, leading to novel industrial applications

19. Thank you! Acknowledgments • Jean-Jacques Sacré for his help and guidance in preparing the experimental setup • Following colleagues for being the observers in the color matching experiments: • Laurent Blondé • Patrick Morvan • Jürgen Stauder • Arno Schubert • Pascal Bourdon • Séverine Baudry • Emmanuel Jolly • Catherine Serre • Jean-Jacques Sacré

20. Appendix: Modern Displays and Observer Metamerism CRT LCD CRT LCD Obs. 1 (cat. 5) Obs. 1 (cat. 5) Obs. 2 (cat. 6) Obs. 2 (cat. 6) All colors refer to CRT