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Visual Evaluation Experiment on Chroma Saturation Effects (Preliminary)

Report for TC1-69, June 1, 2009, Budapest. Visual Evaluation Experiment on Chroma Saturation Effects (Preliminary). Yoshi Ohno NIST, USA. NIST Spectrally Tunable Lighting Facility for color rendering and vision science experiments. Specifications.

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Visual Evaluation Experiment on Chroma Saturation Effects (Preliminary)

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  1. Report for TC1-69, June 1, 2009, Budapest Visual Evaluation Experiment on Chroma Saturation Effects (Preliminary) Yoshi Ohno NIST, USA

  2. NIST Spectrally Tunable Lighting Facility for color rendering and vision science experiments

  3. Specifications • 22 color channels using 1800 high power LEDs/unit (to be expanded) • 17 narrow bands + 5 broad bands (phosphor LEDs) • Each color channel has 5 to 10 W optical power. • Full power total optical power ~200 W, luminous flux ~50,000 lm. • 500 to 800 lx illumination for most of simulated white Light spectra.

  4. “Color Quality Scale” Proposed by NIST • Fix the problems of CRI (based on color fidelity) 1) use 15 saturated reference color samples 2) use the latest color space (CIE LAB) 3) use the latest chromatic adaptation formula (CMCCAT2000) 4) 0 to 100 scale (CRI can have negative score.) 5) CCT factor based on gamut area of ref. Illuminant 6) RMS combining of color differences 7) Scale normalized for consistency with CRI for  fluorescent lamps • Saturation factor – Considers the effect of enhanced color contrast. Davis, W. and Ohno, Y. “Development of a Color Quality Scale (CQS),” Proc., Sixth International Lighting Research Symposium on Light and Color, Orlando, FL, February 2006.

  5. Ref Ref Test Test Saturation factor Score is not penalized for increase of chroma. (Score is decreased for hue and lightness shifts) Score is decreased for the full color difference

  6. Experiments Lights tested • CCT: 4000 K (800 lx) and 3000 K (300 lx), Duv=0.000 • 4000 K 3000 K • Reference: broadband CRI Ra=98 Ra=97 • 4 peak (RGBA) Desaturated-4 Ra=70 Ra=70 • 4 peak (RGBA) Desaturated-3 Ra=77 Ra=76 • 4 peak (RGBA) Desaturated-2 Ra=84 Ra=84 • 4 peak (RGBA) Desaturated-1 Ra=90 Ra=90 • 4 peak (RGBA) Neutral Ra=92 Ra=95 • 4 peak (RGBA) Saturated-1 Ra=87 Ra=88 • 4 peak (RGBA) Saturated-2 Ra=82 Ra=81 • 4 peak (RGBA) Saturated-3 Ra=74 Ra=74 • 4 peak (RGBA) Saturated-4 Ra=69 Ra=69 8 Subjects: 5 Caucasians, 3 Asians / 5 females, 3 males Observation: 1) Look at the objects in the room (do not look at hands/face) 2) Look at your hands and face

  7. 4000 K Broadband Reference

  8. 4000 K Desaturated-4

  9. 4000 K Desaturated-3

  10. 4000 K Desaturated-2

  11. 4000 K Desaturated-1

  12. 4000 K Neutral

  13. 4000 K Saturated-1

  14. 4000 K Saturated-2

  15. 4000 K Saturated-3

  16. 4000 K Saturated-4

  17. 3000 K Broadband (Reference)

  18. 3000 K Desaturated-4

  19. 3000 K Desaturated-3

  20. 3000 K Desaturated-2

  21. 3000 K Desaturated-1

  22. 3000 K Neutral

  23. 3000 K Saturated-1

  24. 3000 K Saturated-2

  25. 3000 K Saturated-3

  26. 3000 K Saturated-4

  27. Neodymium (for comparison)

  28. Results

  29. Results

  30. Additional indices (CQS 7.4) Qa: General Color Quality Scale Qf: Qa without saturation factor Qp: Qa with positive saturation factor Qd: Relative gamut area of 15 samples

  31. NIST Proposal • Color Quality Scale (CQS), Qa, for one number metric. • Additional metrics • 1) Color fidelity index (Qf or Ra) • 2) Color preference index (Qp)

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