Exploring the Concepts of Color and Gloss Jeralyn Camp BYK Gardner May 2-3, 2016 Color stimulates certain Feelings! Color stands for Identification! Color stands for Regulation and Authority! Color influences our Purchasing Decisions! Uniform Color : Multi-component Products Visual Assessment • Color perception is subjective - Age, gender, mood • We cannot communicate nor remember colors - Only names or numbers • Color is dependent on surrounding light • Color is dependent on background Page 8, BYK-Gardner USA, Color Measurement Page 9, BYK-Gardner USA, Color Measurement Colors seem more dramatic against black Colors seem more subdued against white Color Perception Light Source Observer Object Measurement Report illuminant D65 / 10° spectro-guide 45/0 Color Scale Standard Sample Differences L* 36.84 37.77 0.93 a* -24.10 -24.59 -0.49 b* 12.00 11.88 -0.12 dE* = 1.05 Spectrum of Visible Light object White light is a mixture of many colors UV IR Wavelength l (nm) 1 nm = 10-9 m Standard illuminants D65 A F2 E l E l E l 400 500 600 700 400 500 600 700 400 500 600 700 Wavelength [nm] Wavelength [nm] Wavelength [nm] North Sky Daylight Tungsten Fluorescent Ojects look different under different illuminants Measurement Report observer D65 / 10° spectro-guide 45/0 Color Scale Standard Sample Differences L* 36.84 37.77 0.93 a* -24.10 -24.59 -0.49 b* 12.00 11.88 -0.12 dE* = 1.05 Eye Detectors Rods Cones Cones Cones Retina Rod cells Cone cells Lightness detectors at night Color detectors Young/Helmholtz Color Theory Primary wavelengths: 700 nm (red) 546 nm (green) 435 nm (blue) Wright / Guild Experiment Masking Screen Black Partition Observer The Eye and Fields of View 2° observer (1931) • Small area of the retina • Does not agree with color viewing 10° observer (1964) 10° • Large area of the retina • Corresponds with color viewing Standard Observer 2° Observer (1931) 10° Observer (1964) Energy Relative 400 500 600 700 Wavelength (nm) Ishihara`s Test for color deficiency •Dichromacy: only 2 cones are functioning • Red blindness (approx. 1% of male) • Green blindness (approx. 1% of male) • Blue blindness (very seldom: 1-2 in 100,000) •Anomalous Trichromacy: 3 cones – 1 cone is altered • Most popular case (approx. 5.9 % male) e.g. red-green deficiency Color Perception Light Source Observer Object Opaque Samples Incident Light Diffused Reflection Specular Reflection (= Gloss) Opaque Samples: Absorption and Diffusion of Light Specular Reflection Diffused Reflection (= Gloss) Incident light Object Color Spectral Reflectance Curves blue red green yellow The Building Blocks of Color Illuminant Object Observer A 2° A E l × × 400 500 600 700 Wavelength [nm] Color Scales: X Y Z L*a*b*, .... Opponent Color Theory Blue detectors Blue - Yellow Signal B Green detectors Black - White R Signal A I N Red - Green Signal Red detectors Page 29, BYK-Gardner GmbH, Color Measurement Page 30, BYK-Gardner GmbH, Color Measurement CIE L*a*b*-System L* Lightness a* green / red b* blue/yellow L* Lightness C* Chroma (saturation) h° hue angle CIELab - System L* = 100 +b* Yellow L* = + 58,12 -a* a* = + 36,26 Green b* = + 30,41 +a* Red L* = + 58,12 C* = + 47,32 -b* Blue h° = 50° L* = 0 Measurement Report scales D65 / 10° spectro-guide 45/0 Color Scale Standard Sample Differences L* 36.84 37.77 0.93 a* -24.10 -24.59 -0.49 b* 12.00 11.88 -0.12 dE* = 1.05 Metamerism – 2 samples: pigments with different reflectance D65 Daylight % Reflectance match A Tungsten mismatch Metamerism Index MI < 1 (spectrum needed) Instrument´s Display of Metamerism D65/10° A/10° F11/10° dL* = 0,10 dL* = 0,08 dL* = 0,06 da* = 0,05 da* = -1,04 da* = -1,62 db* = 0,05 db* = 0,10 db* = 0,06 dE* = 0,12 dE* = 1,04 dE* = 1,62 Metamerism Index D65/10° - A/10° 1,06 D65/10° - F11/10° 1,64 F11/10° - A/10° 0,57 Limitations of CIELab System E* = (L*)2 + (a*)2 + (b*)2 Sample 1 2 2 2 Standard E * = 0.57 0.57 0.57 = 1 E * = 0.02 1.02 0.02 = 1 Sample 2 Limitations of CIELab System Measured values do not correlate with visual impression All colors within one ellipse are perceived as the same color. • Visual acceptability is based on ellipses not circles: Tolerances for hue are tighter than for chroma • Chromatic colors have larger tolerances than pastels or near neutrals • Size and shape of ellipse change dependent on the hue: Acceptable color differences vary from color to color Green has larger tolerances than dark blue Rectangular versus Elliptical Tolerances ± b* Product Standard Acceptable Match Visually Rejected Match ± a* Improvements of CIELab System •Goal: • Better agreement with visual color perception • One tolerance for all colors = uniform color space dE* dE*CMC 94 DIN99 dE00 ECMC – Color Measurement Committee of The Society of Dyers and Colorists (UK): 1988 • Based on visual evaluation of textile samples • Currently specified in the following standards: - British Standard BS6923 - American AATCC Test Method 173 - ISO International Standard 105-J03 • Based on elliptical (not rectangular) spacing and L*C*H* • Corrects for chroma, hue and lightness dependent perception ECMC – Color Difference Formula lSL 2 2 2 1 2 L * C* H* = ab ab ECMCl:c ÷ ÷ ÷ lSL cSC SH • 3-dimensional ellipsoid with axes corresponding to cSc hue, chroma and lightness SH • Weighting factors (= semi-axis) SL, SC and SH are dependent on color of standard • Application factors l and c to modify the lengths of semi-axes ECMC – Color Difference Formula 2 2 2 dL* dC*ab dH*ab + + dECMC (l:c) = ( lSL ) ( cSC ) ( SH ) Where SL = 0.040975 L1 Sc = 0.0638 C1 + 0.638 1 + 0.01765 L1 1 + 0.0121 C1 Unless L1 < 16 when SL = 0.511 4 1/2 And SH = SC (Tf + 1- f) where f = (C1) (C )4 + 1900 ( 1 ) T = 0.36 + 0.4*cos( h1 + 35) unless h1 is between 164 and 345 when: T = 0.56 + 0.2*cos( h1 + 168) where L1, C1 and h1 relate to the standard ECMC – Color Difference Formula Better correlation to visual perception: Brilliant Yellow with Chroma / ΔHue L* a* b* dL* da* db* dC* dH* dE* dECMC Standard Yellow 84.25 5.74 96.00 Yellow -H 84.46 8.88 96.49 0.22 3.14 0.49 0.73 3.18 1.64 Yellow -C 84.52 5.75 93.09 0.27 0.01 -2.91 -0.19 2.92 0.88 Yellow +C 84.37 5.86 99.42 0.12 0.12 3.43 0.08 3.43 1.02 Color Difference: dE* dL*=1, dC*=1.3, dH*=0.65 Color Difference: dECMC +db* 45° +dL* 2 4 4 Standard; STANDARD 07 L*=84.25; a*=5.74; b*=96 3 3 45° +db* 1 +dL* 2 2 4 4 3 3 1 1 Chromatic colors have larger visual 2 2 -da* +da* 0 0 1 1 -4 -3 -2 -1 0 1 2 3 4 tolerances in chroma than in hue -da* +da* -1 -1 0 0 -4 -3 -2 -1 0 1 2 3 4 -1 -1 -2 -2 -2 -2 -3 -3 -3 -3 -4 -4 -4 -4 -dL* -db* -db* -dL* ECMC – Color Difference Formula Better correlation to visual perception: Brilliant Red with C* vs. Brown (Less chromatic Red) with C* L* a* b* dL* da* db* dC* dH* dE* dECMC Std Brilliant Red 38.64 64.26 52.16 Brilliant Red -C 38.59 62.06 51.11 -0.05 -2.20 -1.05 0.58 2.44 0.84 L* a* b* dL* da* db* dC* dH* dE* dECMC Std Brown 38.83 33.35 26.67 Brown -C 38.69 31.14 25.21 -0.14 -2.21 -1.46 0.24 2.65 1.13 Color Difference: dE CMC Color Difference: dECMC Standard; STANDARD 08 L*=38.64; a*=64.26; b*=52.16 Standard; STANDARD 09 L*=38.83; a*=33.35; b*=26.67 45° Chromatic colors have +db* 1 +dL* 45° +db* 1 4 4 +dL* 4 2 larger visual tolerance 3 3 3 1.5 2 2 than achromatic 2 1 1 1 1 0.5 colors. -da* +da* -da* +da* 0 0 0 0 -4 -3 -2 -1 0 1 2 3 4 -4 -3 -2 -1 0 1 2 3 4 -1 -1 -1 -0.5 -2 -2 -2 -1 -3 -3 -3 -1.5 -2 -4 -4 -4 -db* -dL* -db* -dL* ECMC – Color Difference Formula; Influence of ratio l : c • Ratio l:c allows for a weighting of lightness to chroma L* • Most common ratio: 2:1 Variation in lightness can be double compared to chroma variations L* C* C* H* H* ratio 2:1 ratio 1:1 ECMC – Color Difference Formula Influence of Commercial Factor: cf • Commercial Factor (cf) determines the overall size of the ellipse • cf sets the color tolerance: ECMC < cf PASS E > cf FAIL L* CMC L* C* C* H* H* cf=1.0 cf=0.5 ECMC – Color Difference Formula Influence of Commercial Factor: cf Standard; STANDARD 01 Standard; STANDARD 01 Standard; STANDARD 01 L*=61,62; C*=3,47; h°=263,97 L*=61,62; C*=3,47; h°=263,97 L*=61,62; C*=3,47; h°=263,97 +db* +db* +db* 45° 2 +dL* 45° 2 +dL* 45° 2 +dL* 4 4 2 2 2 2 1,5 1,5 1,5 3 1,5 3 1 1 1 2 1 2 0,5 0,5 0,5 1 0,5 1 -da* +da* -da* +da* -da* +da* 0 0 0 0 0 0 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 -2 -1,5 -1 -0,5 0 0,5 1 1,5 2 -0,5 -0,5 -0,5 -1 -0,5 -1 -1 -1 -1 -2 -1 -2 -1,5 -1,5 -1,5 -3 -1,5 -3 -2 -2 -2 -4 -2 -4 -dL* -db* -dL* -dL* -db* -db* cf = 0.5 cf = 1.0 cf = 1.5 ECMC – Color Difference Formula Summary • One tolerance for all colors: cf = size of the tolerance ellipse • Tolerance is based on elliptical spacing Size and shape of tolerance ellipse is calculated based on Standard location in the color space ECMC - Typical Tolerances l c cf 45° 2 1 0.5 Solids E00 (CIEDE2000) - Color Difference Formula:2001 • Based on several already existing data sets • Currently published in the following CIE recommendation: - CIE Technical Report 142: Improvement to industrial colour difference evaluation • Based on elliptical spacing and L*C*H* • Corrects for lightness, chroma and hue dependent perception ECMC – Color Difference Formula Summary • Better correlation to visual perception: • Chromatic Colors: Larger visual tolerance ellipse ECMC smaller for chromatic colors than for achromatic colors (C* and H* are weighted less) compared to E* • Light Colors: Larger visual tolerance ellipse for lightness ECMC smaller for light colors than for dark colors (L* is weighted less) compared to E* • Visual acceptability most sensitive to 1.