Let‘s talk about Colorimety

Let‘s talk about Colorimetric Basics

Textile Effects Electro-Magnetic Waves

visible light

Textile Effects Different technics of color mixtures

Additive color mixture e.g. used for TV or computer screens or paper graphics

Subtractive color mixture e.g. used for textile dyeing or printing

Textile Effects Relation between reflectance and absorbance

light source human eye

textile sample

The light is either reflected or absorbed by the sample

Textile Effects Reflectance

Reflectance Reflectance factor beta in % I   r %R  100 I0

The reflectance factor is the ratio of the reflected light Ir to the illuminating light I0

Textile Effects Absorbance

Absorbance Absorbance factor in % A  1   %A  1   100

The absorbance factor is the difference between the total, illumuninating light and the reflected light

Both, reflectance and absorbance, are relative factors and independant from the energy distribution of the illuminant

Textile Effects Reflectance Curves/1

Reflectance curce of a yellow shade Reflectance curve of a red shade 1 1

0.9 absorbed light

0.8 0.8

0.7

0.6 0.6

0.5 absorbed light reflected light

0.4 0.4

Reflectancebeta factor Reflectancebeta factor

0.3

reflected 0.2 0.2 light

0.1

0 0 400 500 600 700 400 500 600 700 Wavelength [nm] Wavelength [nm]

Textile Effects Reflectance Curves/2

Reflectance curve of a blue shade Reflectance Curve of a Green Color 0.6 0.6

0.5 0.5

0.4 absorbed light 0.4 absorbed light

0.3 0.3

Reflectancebetafactor Reflectancebeta factor 0.2 0.2

0.1 0.1

reflected light reflected light

0 0 400 500 600 700 400 500 600 700 Wavelength [nm] Wavelength [nm]

Textile Effects Commission International de l‘Éclairage (CIE)

The CIE has defined several standard illuminants: D65 = Average daylight (6500 K) A = Tungsten (incandescent) light (2854 K)

But also fluorescent lamps like: F2 = Cool White Fluorescent CWF (4200 K) F11 = Fluorescent light Philips TL84 (4000K)

The illuminants are defined by its color temperature and the relative spectral energy distribution.

Textile Effects CIE Standard Illuminant D65 Daylight (6500 K)

150

100

50 Relative spectral energyspectralRelative distribution

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects CIE Standard Illuminant A Incandescent light (2854 K)

250

200

150

100

50 Relative spectral energy distribution energy Relative spectral

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects CIE Illuminant F2 Cool White Fluorescent (4200 K)

50

40

30

20

10 Relative spectral energy distribution energy Relative spectral

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects CIE Illuminant F11 Fluorescent light Philips TL84 (4000 K)

100

80

60

40

20 Relative spectral energy distribution energy spectral Relative

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects Human Eye

Cross section of the human Cross section of the retina eye

Textile Effects Human Eye/2

In the retina there are two different types of optical sensors:

Rods for light/dark sensation Cones for color sensation

Cones are sensitive to red or green or blue. CIE has defined the sensitivity of the cones as standard observers for:

10° (large field) 2° (small field)

Textile Effects CIE Standard Observer 10°

2.5 _ z

2.0

1.5 _ _ x y

1.0 Tristimulus values illuminant E illuminant values Tristimulus

0.5

0.0 350 450 550 650 750 Wavelength in nm

Textile Effects The color vision process

CIE Standard Illuminant D65 Reflectance curce of a yellow

(Daylight) 1 shade 150

absorbed light

0.8 textile sample 100

0.6

reflected light

0.4 Reflectancebeta factor

50 Relative spectral energy distribution energy spectral Relative

0.2

0 0 350 400 450 500 550 600 650 700 750 400 500 600 700 Wavelength in nm Wavelength [nm]

light source Reflectance curve

CIE Standard Observer Red CIE Standard Observer Green CIE Standard Observer Blue

1.5 1.5 2.5

_ _ z

x 2.0 _ y

1.0 1.0

1.5

1.0

Tristimulus values Tristimulus

Tristimulus values Tristimulus Tristimulus values Tristimulus

0.5 0.5

0.5

0.0 0.0 380 430 480 530 580 630 680 730 0.0 380 430 480 530 580 630 680 730 380 430 480 530 580 630 680 730 Wavelength in nm Wavelength in nm Wavelength in nm eye sensors

Textile Effects The color vision process/2

3 color signals from a Yellow color

Red Signal of a Yellow Color Green Signal of a Yellow Color Blue Signal of a Yellow Color

100 100 100

80 80 80

60 60 60

40 Y 40

40 X

Tristimulus values Tristimulus D65/10

Tristimulus values Tristimulus D65/10 Tristimulus values Tristimulus D65/10

Z 20 20 20

0 0 0 400 500 600 700 400 500 600 700 400 500 600 700 Wavelength in nm Wavelength in nm Wavelength in nm

Textile Effects CIE Color Coordinates

Calculation of CIE Calculation of CIE Tristimulus Values chromaticity coordiantes

700 _ X X  k   S  x   x  400 X  Y  Z 700 _ Y y  Y  k   S  y   X  Y  Z 400 _ Z 700 z  Z  k   S  z   X  Y  Z 400

S = illuminant e.g D65  The sum of x+y+z x,y,z = CIE standard observer is always 1.  = reflectance factor k = normalization factor

Textile Effects CIE 1931 chromaticity diagram

Textile Effects Let‘s talk about Color difference and tolerances

Textile Effects MacAdam Ellipses

The MacAdam ellipses define the visible color difference perceptibilty within the CIE diagram. They show, that the CIE x,y,Y color space is not equidistant to our visual perception.

Textile Effects Uniform Color Spaces

To improve the non-uniformity of the CIE 1964 color space, several transformation from x,y,Y color space to systems with better uniformity have been developed, e.g. :

Hunter : L, a, b Adams-Nickerson : ANLAB CIE 1976 : L*, a*, b*

Textile Effects CIE 1976 Color Space

Lightness L* L* 116 Y*16

Red-Green axis a* a* 500(X*Y*)

Yellow-Blue axis b* b* 200(Y*Z*)

2 2 1/2 Chroma C*ab Cab*  (a * b * )

Hue h b * ab hab  arctan( ) a *

Textile Effects Calculation of CIELab difference

dL* = L*sample - L*standard Lightness + = lighter - = darker difference:

da* = a*sample - a*standard Red - Green difference : + = redder - = greener

Yellow-Blue difference: db* = b*sample - b*standard + = yellower - = bluer

2 2 2 1/2 Total colour difference:: dEab*  ((dL*)  (da*)  (db*) )

approximate perceptibility = 0.2 - 0.5

Textile Effects Calculation of CIELCH difference

dL* = L*sample - L*standard Lightness difference : + = lighter - = darker

dCab* = Cab*sample - Cab*standard Chroma difference : + = brighter - = duller

2 2 1/2 Hue difference : dH*  ((dEab * (dL*)  (dC*) )

Red + = yellower - = bluer The interpretation is Yellow + = greener - = redder depending on the hue, Green + = bluer - = yellower e.g. : Blue + = redder - = greener

Textile Effects Production Control - Color tolerances

The CIE-Lab color space is, like the CIE-x,y,Y color space, visually not equidistant. The uniformity has been improved, but is not yet perfect. Therefore tolerances have to be defined for each color. Also the different visual sensitivity of lightness- chroma- or hue-differences has to be considered. To define tolerance limits, sufficient and reliable visual jugements are necessary. Around each standard color up to 50 trials should be distributed evenly and a minimum of 20 to 30 colorists should assess the differences - this means a total of 1000 visual assessments for each colour.

Textile Effects Production Control - Pass/fail formulas

To avoid the huge effort of defining tolerances for each color, the CIELab color space has been modified by weighting the lightness- chroma- and hue difference in the formula, using large data sets from the industry. Some of this modified formulas are: JPC79 (J.P.Coats) CMC (l:c) (Colour Measurement Committee, UK) BFD (l:c) (Bradford university, UK) (l:c is the ratio of lightness and chroma, recommended is 2:1) M&S89 (Marks & Spencer) Datacolor

ISO recommends the CMC (l:c) formula for small color differences (ISO/DP 105-J01).The CMC (l:c) formula has some disadvantages in the blue range of the color space. This has been improved with the BDF(l:c) formula, but there is not enough experience to tell if BDF is generally better than CMC.

Textile Effects CIE-Lab Tolerancing

CIE-Lab defines a cubic color space, which does not always correlate with our visual perception

Textile Effects CIE-LCH Tolerancing

CIE-LCH coordinates define a cylindrical color space. The correlation with our visual perception is much better.

Textile Effects CMC Tolerancing

CMC uses tolerance ellipsoids, which have different shapes within the color space. They have been adapted to visual color perception

Textile Effects Let‘s talk about Metamerism and Color Constancy

Textile Effects Metamerism

Same colors under Different colors under daylight illumination shop illumination

Textile Effects Metameric colors under D65

Brown 1 Brown 2

Textile Effects Metameric colors under TL84

Brown 1 Brown 2

Textile Effects Metamerism

If a pair of samples looks identical under a particular illuminant, but different under another light source, the samples are described as metameric. They have different reflectance curves and produce different sets of color co-ordinates under different light sources. In colorimetry, metamerism is defined using a metamerism index.

Textile Effects Reflectance Curves of metameric Colors

0.8

Brown No. 1

0.6 Brown No. 2

0.4 Reflectancebetafactor

0.2

0 400 450 500 550 600 650 700 Wavelength [nm]

Textile Effects Metamerism Index

lluminant Co-ordinates Brown 1 Brown 2

D65/10 L* 35.1I 34.4

a* 5.8 4.3

b* 10.0 8.8

CIELab difference dE Standard 2.0

A/10 L* 51.9 52.0

a* 7.8 15.8

b* 7.0 5.5

Metamerism Index dE Standard 6.5

TL84/10 L* 51.6 50.2

a* 9.0 15.0

b* 4.0 2.9

Metamerism Index dE Standard 10.1

Textile Effects Color Constancy

Same colors under Same colors incandescent under daylight lamp, but different illumination from daylight

Textile Effects Color Inconstancy of a green color

Green color under Beige color under illuminant D65 illuminant A

Textile Effects Color Constancy

If one sample changes color appearance when it is illuminated using a different light source, we talk about good or inadequate color constancy of the sample. The different spectral energy distribution of the light source in combination with the reflectance curve of the sample results in a change in color appearance. In colorimetry, color constancy is defîned by a color inconstancy index.

Textile Effects Color Constancy/2

Reflectance curve of a green shade 1

0.8

0.6

0.4 Reflectance factor beta

0.2

0 400 500 600 700 Wavelength [nm]

Textile Effects CIE Standard Illuminant D65 Daylight (6500 K)

150

100

50 Relative spectral energyspectralRelative distribution

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects CIE Standard Illuminant A Incandescent light (2854 K)

250

200

150

100

50 Relative spectral energy distribution energy Relative spectral

0 350 400 450 500 550 600 650 700 750 Wavelength in nm

Textile Effects Color Constancy Index

Reflectance data

Color Co-ordinates Color Co-ordinates reference illuminant test illuminant

Lr, ar, br Lt, at, bt

Color Chromatic difference adaptation

Color Co-ordinates Inconstancy chromatic adapted Index dE Lc, ac, bc

Textile Effects Color Constancy Index/2

D65/10 A/10 Color reference Color test illuminant Color Chromatic Coordinates illuminant Coordinates Coordinates adapted

L*r 56.6 L*t 56.8 L*c 56.6

a*r -4.6 a*t 3.5 a*c 2.3

b*r 9.3 b*t 7.4 b*c 6.7

Difference

dL* 0.0

da* 6.9

db* -2.6

Inconstancy Index

dE 7.3

Textile Effects Main source of metamerism problems (between standard sample and actual dyehouse dyeing)

Designers chose shades from substrates different from intended textile, colored with very different trichromies

Examples :

From a PANTONE color selector, in which case the color has been obtained by printing on paper, with a trichromy of: => greenish yellow („Yellow“) => pinkish red („Magenta“) => turquoise („ Cyan“)

This is much different from a typical textile trichromy , usually based upon: => golden yellow => bluish red => reddish or neutral blue or navy

Other supports of designer inspiration: plastic, wood, foliage, photos ...

Textile Effects Main source of metamerism problems (between standard sample and actual dyehouse dyeing)

Designers chose shades from substrates different from intended textile, colored with very different trichromies

This „original“may have good- or poor color constancy. Along the communication line, the shade samples are matched as non- metameric compared to this original sample .

The prefered, often most robust-, fast- and economical trichromies used in dyehouses do not always allow a non-metameric shade compared to such standards

Textile Effects Main source of metamerism problems (between standard sample and actual dyehouse dyeing)

Metamery caused by the initial choice by designers of a colored original which coloration is not based on a textile dyers logic

is causing problems all along the textile logistical chain => technically- or economically sub-optimal dyeing recipes => waste of time and high cost

Textile Effects Let‘s talk about Spectrophotometer settings and sample preparation

Textile Effects Spectrophotometer settings and sample preparation

To guarantee exact color measurements, the settings of the spectrophotometer and the preparation of the samples have to be defined clearly. The following parameters can have a large influence on the measurement:

• Specular component included or excluded • UV component included, calibrated or excluded • Aperture size • Number of sample layers • Number of readings per sample • Conditioning of the sample

Textile Effects Influence of specular component

0.6 0.6

Blue 24 specular included Blue 24.2 specular excluded

Blue 24.2 specular included 0.5 Blue 24 specular excluded 0.5

Substrate: Acetate Woven Satin Substrate: Acetate Woven Satin

0.4 0.4

0.3 0.3

Reflectancebetafactor Reflectancebetafactor

0.2 0.2

0.1 0.1

0 0 400 450 500 550 600 650 700 400 450 500 550 600 650 700 Wavelength [nm] Wavelength [nm]

Textile Effects Influence of specular component/2

Standard: Blue 24 specular excluded ---- Illuminant/Observer ---- Sample: Blue 24 specular included D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.62 0.63 0.64

Standard: Blue 24.2 specular excluded ---- Illuminant/Observer ---- Sample: Blue 24.2 specular included D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.63 0.64 0.64

Textile Effects Influence of specular component/3

Standard: Blue 24 specular excluded ---- Illuminant/Observer ---- Sample: Blue 24.2 specular excluded D65/10 CWF/10 A/10

CMC(2:1) dE CMC 1.79 1.87 1.84

Standard: Blue 24 specular included ---- Illuminant/Observer ---- Sample: Blue 24.2 specular included D65/10 CWF/10 A/10

CMC(2:1) dE CMC 1.79 1.87 1.84

Textile Effects Influence of specular component/4

Standard: Blue 24 specular excluded ---- Illuminant/Observer ---- Sample: Blue 24.2 specular included D65/10 CWF/10 A/10

CMC(2:1) dE CMC 2.43 2.53 2.51

Textile Effects Influence of UV component

1.5 1.2

Blue 2BR with full UV Red 4BS with full UV Blue 2BR with UV calibrator Red 4BS with UV calibrator Blue 2BR with cutoff FL 400 1.25 1 Red 4BS with cutoff FL 400

Substrate: PES Jersey with FWA Substrate: PES Jersey with FWA

1 0.8

0.75

0.6 Reflectance/Emissionfactor

0.5 Reflectance/Emissionfactor 0.4

0.25 0.2

0 380 430 480 530 580 630 680 0 380 430 480 530 580 630 680 Wavelength [nm] Wavelength [nm]

Textile Effects Influence of UV component/2

Standard: Blue 2BR with full UV ---- Illuminant/Observer ---- Sample: Blue 2BR with UV calibrator D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 2.67 2.56 2.13

Standard: Blue 2BR with full UV ---- Illuminant/Observer ---- Sample: Blue 2BR with cutoff FL 400 D65/10 CWF/10 A/10

CMC(2:1) dE CMC 11.50 10.56 8.46

Textile Effects Influence of UV component/3

Standard: Red 4BS with full UV ---- Illuminant/Observer ---- Sample: Red 4BS with UV calibrator D65/10 CWF/10 A/10

CMC(2:1) dE CMC 1.93 2.33 2.17

Standard: Red 4BS with full UV ---- Illuminant/Observer ---- Sample: Red 4BS with cutoff FL 400 D65/10 CWF/10 A/10

CMC(2:1) dE CMC 7.96 9.82 8.56

Textile Effects Influence of sample layers

1 1

Blue 1 layer / white 0.9 0.9 Blue 1 layer / black Blue 2 layers / white Blue 2 layers / black 0.8 0.8 Blue 4 layers / white Blue 4 layers / black

0.7 0.7 Substrate: PES Micro woven

0.6 0.6

0.5 0.5

Yellow 1 layer / white

0.4 Yellow 1 layer / black 0.4

Reflectancebetafactor Reflectancebetafactor Yellow 2 layers / white Yellow 2 layers / black 0.3 0.3 Yellow 4 layers / white Yellow 4 layers / black Yellow 8 layers / white 0.2 0.2 Yellow 8 layers / black

Substrate: CO knitwear 0.1 0.1

0 0 400 450 500 550 600 650 700 400 450 500 550 600 650 700 Wavelength [nm] Wavelength [nm]

Textile Effects Influence of sample layers/2

Standard: Yellow CO knit 1 layer/white ---- Illuminant/Observer ---- Sample: Yellow CO knit 1 layer/black D65/10 CWF/10 A/10

CMC(2:1) dE CMC 4.91 4.91 5.17

Standard: Yellow CO knit 2 layers/white ---- Illuminant/Observer ---- Sample: Yellow CO knit 2 layers/black D65/10 CWF/10 A/10

CMC(2:1) dE CMC 1.47 1.29 1.52

Textile Effects Influence of sample layers/3

Standard: Yellow CO knit 4 layers/white ---- Illuminant/Observer ---- Sample: Yellow CO knit 4 layers/black D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.12 0.09 0.13

Standard: Yellow CO knit 8 layers/white ---- Illuminant/Observer ---- Sample: Yellow CO knit 8 layers/black D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.10 0.10 0.10

Textile Effects Influence of sample layers/4

Standard: Blue PES micro 1 layer/white ---- Illuminant/Observer ---- Sample: Blue PES micro 1 layer/black D65/10 CWF/10 A/10 CMC(2:1) dE CMC 1.10 1.11 0.97

Standard: Blue PES micro 2 layers/white ---- Illuminant/Observer ---- Sample: Blue PES micro 2 layers/black D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.06 0.05 0.06

Standard: Blue PES micro 4 layers/white ---- Illuminant/Observer ---- Sample: Blue PES micro 4 layers/black D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.04 0.04 0.03

Textile Effects Influence of readings

Standard: Peach 1 reading/1 ---- Illuminant/Observer ---- Sample: Peach 1 reading/2 D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.07 0.07 0.07

Standard: Peach 2 readings/1 ---- Illuminant/Observer ---- Sample: Peach 2 readings/2 D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.04 0.04 0.04

Standard: Peach 3 readings/1 ---- Illuminant/Observer ---- Sample: Peach 3 readings/2 D65/10 CWF/10 A/10 CMC( 2:1) dE CMC 0.03 0.03 0.04

Textile Effects Influence of readings/2

Standard: Red 1 reading/1 ---- Illuminant/Observer ---- Sample: Red 1 reading/2 D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.05 0.05 0.05

Standard: Red 2 readings/1 ---- Illuminant/Observer ---- Sample: Red 2 readings/2 D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.04 0.04 0.04

Standard: Red 3 readings/1 ---- Illuminant/Observer ---- Sample: Red 3 readings/2 D65/10 CWF/10 A/10 CMC(2:1) dE CMC 0.01 0.01 0.01

Textile Effects Influence of light exposure (Photochromie)

Standard: Beige 1 ---- Illuminant/Observer ---- Sample: Beige 1 after 2h exposer D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.23 0.19 0.19

Standard: Beige 1 ---- Illuminant/Observer ---- Sample: Beige 1 after 4h exposer D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.25 0.20 0.20

Textile Effects Influence of light exposure/2 (Photochromie)

Standard: Beige 1 ---- Illuminant/Observer ---- Sample: Beige 1 after 6h exposer D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.24 0.17 0.18

Standard: Beige 1 ---- Illuminant/Observer ---- Sample: Beige 1 after 24h in the dark D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.06 0.08 0.06

Textile Effects Influence of light exposure/3 (Photochromie)

Standard: Beige 2 ---- Illuminant/Observer ---- Sample: Beige 2 after 2h exposer D65/10 CWF/10 A/10

CMC(2:1) dE CMC 0.09 0.08 0.07

Standard: Beige 2 ---- Illuminant/Observer ---- Sample: Beige 2 after 4h exposer D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.13 0.11 0.10

Textile Effects Influence of light exposure/4 (Photochromie)

Standard: Beige 2 ---- Illuminant/Observer ---- Sample: Beige 2 after 6h exposer D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.12 0.12 0.11

Standard: Beige 2 ---- Illuminant/Observer ---- Sample: Beige 2 after 24h in the dark D65/10 CWF/10 A/10

CMC( 2:1) dE CMC 0.11 0.13 0.14

Textile Effects