COLOR CATEGORIES IN VARIOUS COLOR SPACES Hirohisa Yaguchi Dept. of Information and Image Sciences Chiba University The 9th CIC (Nov. 8, 2001) Scottsdale, AZ

CONTENTS Importance of color name Review of development of color spaces Experiment on categorical color naming Application; Categorical color rendering index

Importance of Color Name To communicate color information in every day life. To categorize objects and recognize them. Color names do not depend on viewing condition.

Berlin and Kay’s basic color

Eleven basic color names in OSA color space (Boynton and Olson, 1987)

What Color Space Should We Map Color Name? Object color space; OSA, Munsell System Color stimulus space; XYZ Nonlinear scale + complete chromatic adaptation space, CIELAB Viewing condition independent color space: NCS, CIECAM97s

Human color vision and advance of colorimetry

Basic colorimetric system LMS (Physiological system) RGB (Physical system) XYZ (Mathematical system)

LMS (Physiological colorimetry)

RGB (Physical colorimetry)

XYZ (Mathematical colorimetry)

CIELAB(CIE1976L*a*b*) Color adaptation – White is always white Non-linearity – Physical unit to psychological unit Color opponency – Luminance and chromaticness

CIELAB color space

Hunt94 Hunt91 RLAB96RLAB93 Nayatani97 Nayatani94 (CIE ) CIECAM97s CIECAM97c Bradford-Hunt96S Bradford-Hunt96C LLAB96bLLAB Luo Nayatani Fairchild Hunt CIE Others CIELAB （ uniform color space,CIE 1976) CIELUV (uniform color space,CIE 1976) von Kries (chromatic adaptation transform, von Kries1902 von Kries (chromatic adaptation transform, von Kries1902) ZLAB ATD (color perception and visual adaptation, Guth 1995) History of Color Appearance Models

CIE Color Appearance Model (CIECAM97s)

CIECAM97s Color Space

What Color Space Should We Map Color Name? Object color space; Munsell System Color stimulus space; XYZ Nonlinear scale + complete chromatic adaptation color space, CIELAB Viewing condition independent color space: CIECAM97s

EXPERIMENT

Light Sources

Spectral Power Distributions of Light Sources (1)

Spectral Power Distributions of Light Sources (2) ILNXNH MHLH HF

Color Samples Named Basic Color in the Munsell Color System (1)

Color Samples Named Basic Color in the Munsell Color System (2)

Color Samples Named Basic Color in the Munsell Color System (3)

Results in the Munsell Hue Circle

Color samples consistently sorted into the same category of color name for typical three illuminants: D65, IL and H

Color name regions in the CIE 1931(x, y) diagram (D65, IL, H)

Color name regions in the CIE 1976 (a*, b*) plane (D65, IL, H)

Color name regions in the CIECAM97s hue circle (D65, IL, H)

Color name region determined by the OR-region for all illuminants

Color name regions in the CIECAM97s hue circle (All illuminants)

White, Gray and Black in the (C, J) Plane

Red and Pink in the (C, J) Plane

Orange and Brown in the (C, J) Plane

Blue and Green in the (h,J) Plane

Specification of color name regions in the CIECAM97s space Hmin Hmax Cmin Cmax

Color name regions in the CIECAM97s space 75<J55<J<75 35<J<55J<35

Application of Color Name Map Color name reproduction in imaging technology Gamut mapping keeping color name constant Color rendering index of light sources based on categorical color rather than color difference

Color Chips under Different Illuminant

How to calculate ● CCRI for each test sample ● Averaged CCRI Categorical color rendering index (CCRI) × × × × Boundary of color samples under the test light source “St” Boundary of color samples under D65 × × × × Cmax HminHma x Cmin Chroma Hue angle Boundary of Color name “Si”

Relation between CCRI and R a

Conclusions Eleven basic color name regions are clearly separated in the CIECAM97s color space The CIECAM97s provides a good prediction of basic color name under various light sources Color name map in CIECAM97s can be applied to many fields including imaging technology

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