Les couleurs Plan du chapitre : Transmission de la lumière Spectrophotométrie Psychométrie Les espaces colorimétriques GATF’s modern, well equipped color and appearance research laboratory is always available to help you with special problems, techniques, or just questions. Feel free to call, we would like to help you.

Transmission de la lumière Non-Métal opaque LUMIÈRE INCIDENTE RÉFLECTION SPÉCULAIRE DIFFUSE RÉFLECTION Color is seen in the diffuse reflection of a non-metallic object. Shininess or gloss is seen in the specular reflection which is most often less than 4% of the total reflected light.

Transmission de la lumière Métal RÉFLECTION SPÉCULAIRE LUMIÈRE INCIDENTE DIFFUSE RÉFLECTION Color is seen in the specular reflection of a metallic object. Diffuse reflection (if any) is associated with the smoothness of the surface. A highly polished, mirror-like surface would have no diffuse reflection.

Transmission de la lumière Matériel translucide LUMIÈRE INCIDENTE Color can be seen either by diffuse reflection or by diffuse transmission in a translucent object. The choice of instrumental measurement depends upon how a visual judgment is made. These materials can exist as solids or liquids. They are optically complex and require special measurement techniques. Many common materials can be considered translucent - plastics, paper, textiles, beverages (orange juice, milk) are a few of the many examples. When measuring the diffuse reflection of these materials, the thickness of the specimen and the color of the material behind the specimen during the measurement process can significantly affect the measurement data. Therefore, thickness and backing must always be specified and held constant when measurements are taken at different times or locations. DIFFUSE TRANSMISSION DIFFUSE RÉFLECTION RÉFLECTION SPÉCULAIRE

Transmission de la lumière Matériel transparent LUMIÈRE INCIDENTE DIFFUSE TRANSMISSION Color can be seen by regular transmission in transparent materials. These materials can exist as solids or liquids. Perfectly clear materials have no diffuse transmission. The presence of surface texture or internal particulate matter can cause a scatter of light which is generally seen as haze or “cloudiness”. Haze is the ratio of diffuse transmission relative to total transmission. Changes in the thickness of the material can significantly affect the measurement data. Therefore, thickness should be held constant for subsequent measurements. TRANSMISSION RÉGULIÈRE RÉFLECTION SPÉCULAIRE

Isaac Newton a découvert qu’il y a de la couleur dans le blanc Transmission de la lumière Composition de la lumière Isaac Newton a découvert qu’il y a de la couleur dans le blanc

Distribution d’énergie spectrale Transmission de la lumière Composition de la lumière X- RAYS Rayons Gamma UV MICRO- WAVES TV RADIO Énergie Électrique Rayons Cosmiques Infrarouge .00001nm .001nm 1nm 10nm .01cm .1 m 10 m 100m 106m ULTRAVIOLET Spectre visible Infrarouge 300 nm 450 550 650 1000 nm Lumière du jour Distribution d’énergie spectrale Énergie relative Visible light is a small part of the broad electromagnetic spectrum. Light can be specified by its wavelength, for which the nanometer (nm) is the prescribed unit of length.One nanometer equals 1 x 10-9 meters. Earlier reference books referred to this unit as a milli-micron (m). The light from any source can measured with a spectroradiometer and numerically be specified in terms of the relative power (or amount of light) emitted at each wavelength. Plotting this power as a function of the wavelength gives the spectral power distribution curve of the light source. For the purpose of Standardization, the International Commission on Illumination, also known as the C.I.E. (initials of the French words, “Commission Internationale de l’Eclairage”), established Standard sources and illuminants... Longueur d’ondes [nm]

Spectrophotométrie Courbe spectrophotométrique - Orange Reflected (or transmitted) light can be measured with an instrument called a Spectrophotometer -- an electro-optical device which measures the relative amount of light energy at each wavelength. This remains; however, a physical quantification, (how much energy is present at each wavelength) and has little meaning for the way humans actually perceive these light waves, which is called a Psychophysical analysis.

Spectrophotométrie Courbe spectrophotométrique - Vert

Spectrophotométrie Courbe spectrophotométrique - Bleu

Couleur est une sensation… Psychométrie Couleur est une sensation… Et chaque personne les perçoivent différemment.

Psychométrie Psychométrie : prise en compte du sensible, de l’émotion. Dépend de la culture. Rouge : Amour, force, enthousiasme ... Danger, violence Jaune : luminosité, tonique associé au soleil et or Orange : chaleur, lumière ... Vert : apaisement, détente, repos, printemps ... Bleu : Calme et fraîcheur : ciel, mer, espace ... Dépression : le "blues" Violet : rêverie, utopie, mysticisme. . .

Mélange temporel http://home.sharpdots.com/resources/color.cfm?HDID=GP

L’œil Illusions d’optique

Les espaces colorimétriques TSL : teinte – saturation - luminosité Teinte (hue) Saturation (saturation) Luminosité (value)

Les espaces colorimétriques Munsell (HVC) Teinte (hue) Saturation (chroma) Luminosité (value) The neutral chips can be logically arranged in a series from black to white in terms of a single varying quality, lightness, or sometimes referred to as value. The colored chips offer a more complicated situation because they differ from one another in several ways, other than by simple differences in lightness. One way to further organize the chips would be by their hue: red, green, yellow, blue, etc. Noticing that there is a group of reds that are distinctly different from one another, one might discover that there is a third quality of color related to how much color, or saturation or chroma they contain. Thus one might discover that there are three quantities, or color coordinates, that must be specified to describe color.

Les espaces colorimétriques Munsell (HVC) The Munsell Color System was created by the artist Albert H. Munsell in the year 1905. It has been used extensively by artists and designers. In this system, hue is arranged around a vertical axis of neutral colors with the more saturated colors at the outer edges. Disadvantages: The specification of color in the Munsell system is subjective. The description of color in the Munsell system does not necessarily describe the appearance, The Munsell system is not a continuous scale - specification of a color between 2 chips is difficult. Advantages: The 3 dimensions of the Munsell system - lightness, chroma and hue - match the word descriptors people often use to communicate color. Visually uniform - the difference in color between any 2 adjacent chips remains constant. The Munsell color chips can be specified in a numerical form. The color chips provide a physical reference of a color for use as a product standard. The Munsell color chips are available in books, sheets or fan decks with a matte or glossy finish. Many artists and designers still use this system today. They determine which chip is closest in color to their desired color. The specification is then given to another person who may then look at their own book to see the actual color being described.

Les espaces colorimétriques Munsell (HVC) 8 7 6 5 4 3 2 7.5 YR 7/16 7.5 YR 7/16 The specification of color in the Munsell system is unfortunately a subjective specification. The specification of an orange in the Munsell system might be: 7.5 YR 7/16 7.5 YR is the hue; in this case yellow-red 7 indicates the value of lightness level 16 indicates the chroma or saturation level While 3 attributes must be specified to describe color, this does not completely describe the appearance of objects. Let’s now see how it is possible to quantify these 3 attributes. Valeur 2 4 8 12 16 Chroma

Les espaces colorimétriques NCS

Les espaces colorimétriques Stimulus de couleurs Sous des conditions bien spécifiées, la perception des couleurs est reproductible Environnement neutre Oeil reposé. Luminances dans le domaine de fonctionnement optimal des cônes. champ angulaire de 2° (fovea). Mode fenêtre. On parle alors de Stimulus l [S] Le(l) Courbe spectrale Stimulus de couleur

Les espaces colorimétriques Synthèse additive Différentes courbes spectrales peuvent produire le même stimulus (classe d’équivalence). On sait définir une égalité des stimuli [S] = [S’] La superposition des lumières (synthèse additive) passe au quotient Le(l) = L(1)e(l) + L(2)e(l)  [S] = [S1] + [S2] La multiplication scalaire passe au quotient Le(l) = k L(1)e(l)  [S] = k [S1] Ça semble parfaitement évident, mais en fait ça ne l’est pas : c’est faux pour la « synthèse soustractive » (filtres) c’est faux si on sort du domaine de fonctionnement de l’œil (éblouissement)

Les espaces colorimétriques Triplet RGB Trois couleurs de base (primaires) [R], [G], [B] permettent de reproduire l’ensemble des couleurs observables. Par égalisation on définit le triplet (RGB) : [S] = R [R] + G [G] +B [B] Possibilité de composantes négatives ! Choix usuel des primaires (CIE 1930) [R] , [G] , [B] : [R] monochromatique l = 700 nm [G] monochromatique l = 546.1 nm [B] monochromatique l = 435.8 nm Intensités telles que [E] = [R] + [G] + [B] Où [E] est le stimulus associé au blanc de spectre énergétique constant

Les espaces colorimétriques Triplet RGB Le triplet RGB ainsi construit constitue la « mesure » du stimulus [S] Remarque : Les luminances visuelles de primaires RGB sont très différentes. Lv(G) = 4,5907 Lv(R) Lv(B) = 0,0601 Lv(R) Ainsi la luminance visuelle totale d’ un stimulus [S] est donnée par : Lv(S) = Lv(R) ( 1. R + 4.5907 G + 0.0601 B )

Les espaces colorimétriques Triplet RGB [B] [G] [R] [S] G R B Espace des couleurs (R,G,B) Esp. Vectoriel 3 dimensionnel, base ([R],[G],[B]) Pas de métrique, pas de produit scalaire !! La luminance est une forme linéaire La synthèse additive est la somme vectorielle Les stimuli « physiques » forment un sous-ensemble convexe dont le bord correspond aux stimuli monochromatiques (spectrum locus) : tout stimulus est en effet synthèse additive de lumières monochromatiques.

Les espaces colorimétriques Diagrammes de chromaticité (Maxwell 1855) [B] [G] r b g s Diagramme de Chromaticité [B] [G] [R] [S] Diagramme de chromaticité e [E] s

Les espaces colorimétriques Diagrammes de chromaticité (Maxwell 1855) Fonctions colorimétriques : coordonnées des stimuli monochromatiques l dLe = Le(l) dl Le(l)  … après un long travail sur une vingtaine de sujets, Guild obtient les « Matching functions » de l’observateur standard

…ce qui permet de tracer le diagramme RGB de l’ensemble des couleurs : Les espaces colorimétriques Diagramme RGB …ce qui permet de tracer le diagramme RGB de l’ensemble des couleurs :

Les espaces colorimétriques Diagramme CIE XYZ (1931) Un changement de base ([R],[G],[B])  ([X],[Y],[Z]) permet de situer l’ensemble des stimuli physiques dans le « premier quadrant » : X = 2,7689 R + 1,7518 G + 1,1301 B Y = 1,0000 R + 4,5907 G + 0,0601 B Z = 0,0000 R + 0,0565 G + 5,5943 B La transformation est de plus choisie pour que : -   l’espace soit le plus homogène possible , Y représente directement la luminance visuelle , Une grande partie du SL corresponde à Z=0 . Toutes les structures vues en RGB se retrouvent dans le système XYZ …

les coordonnées chromatiques Les espaces colorimétriques Diagramme CIE XYZ (1931) les coordonnées chromatiques … en particulier : Les fonctions colorimétriques , coordonnées du Spectrum Locus

Valeurs ‘Tristimulus’ pour Orange Les espaces colorimétriques Diagramme CIE XYZ (1931) Valeurs ‘Tristimulus’ pour Orange X = 41.73 Y = 33.77 Z = 2.34 Tristimulus values calculated for CIE Illuminant D65 and the 10º standard observer. (Note these numbers will change for different illuminant/observer combinations). If the orange was not directly next to these numbers, would you be able to imagine what color the numbers represented? Probably not, most people can't. While the Y correlates with the perception of lightness (Zero for black and 100 for white), X and Z by themselves do not correlate with hue, saturation, redness-greenness or any other visually meaningful attribute of object color appearance. One way to possibly help understand what the X, Y, and Z numbers mean is to think of the values as amounts of red, green and blue lights being mixed together on a white background.

Les espaces colorimétriques Diagramme CIE XYZ (1931) L’espace ainsi obtenu n’est toujours pas pourvu d’une métrique homogène, comme le montre le diagramme des seuils de perception. y x

Les espaces colorimétriques Diagramme CIELAB (1976) Après plusieurs tentatives une transformation non linéaire est couramment adoptée : Qui redonne une forme de « solide des couleurs » à peu près satisfaisante

Les espaces colorimétriques Diagramme CIELAB (1976) Ce système est conçu pour caractériser la couleur des objets observés en réflexion (mode objet) sous un illuminant standard. Par construction on a LI* = 100 aI* = 0 bI* = 0 pour tenir compte des effets d’adaptation. On définit la chroma : C* = (a* 2 + b* 2) 1/2 et l’angle de teinte : h = arctan(b* / a*) la métrique correspond mieux aux distances colorimétriques perçues par l’œil (Munsell). est couramment adopté par les professionnels de la couleur.

Sources lumineuses ‘Illuminants’ CIE Light Sources and Illuminants Light sources can be either man-made (lamps, etc.) or naturally occurring (sun, electro or chemical luminescence, etc.). An Illuminant is defined by a specific spectral power distribution, and it may or may not be possible to make a source that represents it. Illuminants A, and F2 are both sources and illuminants. However, CIE Illuminant D65 has a defined spectral power distribution representing the average of natural daylight measurements from around the world, yet no artificial source has been found to exactly duplicate the definition. We have now quantified and standardized light, the first of the three elements of visual observation. Let’s now examine what happens when light interacts with the second element, the Object… We have shown how the CIE has standardized various light sources as illuminants. The next component in the Human Visual Observation is the object .

‘Illuminants’ communs • A represents an incandescent tungsten light source having correlated color temperature (CCT ) of 2856K. • C represents an older version of daylight with a CCT of 6774K. • D65 is the most commonly used daylight illuminant with a CCT of 6504K. • D50 is a more spectrally balanced daylight illuminant with a CCT of 5000K used by the graphic arts industry for viewing colored transparencies and prints. • D55 represents daylight having a CCT of 5500K. • D75 represents daylight having a CCT of 7500K. • F2 (Fcw, CWF, F) is one of a series of 12 CIE fluorescent illuminants. It represents the spectral quality of the most common fluorescent lamp, cool white fluorescent with a CCT of 4200K. • TL84 is a custom tri-phosphor illuminant representing a Philips fluorescent lamp with a CCT of 4100k found in Marks & Spencer stores in Europe. • Ultralume 30U is a custom tri-phosphor illuminant for a Philips fluorescent lamp with a CCT of 3000K found in Sears stores in the United States. The illuminants that are most often used are A, C, D50, D65, and F2. Of these five, D65 is in greatest use in the majority of industrial applications except for the graphic arts industry which has standardized on the Illuminant D50.

Système de coordonnées L* a* b* Système de coordonnées de couleurs L = 100 +b JAUNE -a VERT +a ROUGE L, a, b Values A three axis opponent colors scale system based on the theory that color Is perceived by black or white (L), red or green (a), and yellow or blue (b) sensations. -b BLEU L = 0

L = 58.12 a = + 30.41 b = + 36.26 100 CLARTÉ BLANC JAUNE VERT ROUGE -20 -60 -40 +20 +40 +60 VERT +60 +40 +20 Orange color values plotted in three-dimensional L,a,b color space. Notice the similarity to the original Munsell system: Hue - rotating around the "a", "b" axes Chroma or Saturation - out any one single axis Value or Lightness - up or down the "L" axis. ROUGE -20 -40 -60 CLARTÉ BLEU NOIR

Comparaison entre Hunter L,a,b et CIE L*a*b Comparison of Color Values Both examples were evaluated for 10o Observer/Illuminant D65. Notice the similarity of the "L's" and the "a's". Notice the large difference in the "b's" --- this illustrates the "overexpansion" of CIELAB in the yellow region of color space. Always remember that L,a,b values have no meaning whatsoever unless the following are IDENTIFIED: 1. Scale - CIELAB or Hunter 2. Illuminant (A, C, D50, D65, D75, TL84, U30, or ??) 3. Observer (2º or 10º) 4. Instrument Geometry (0º/45º D/8º sphere specular include or exclude or ??) 5. Specific measurement procedure - number of readings, averaging, thickness, backing, temperature, humidity, orientation, etc. L = 58.12 a = +30.41 b = +36.26 L* = 64.79 a* = +32.21 b* = +83.43

COLOR DIFFERENCE Let’s now begin to use these color scales in a more practical manner for communicating color differences, acceptability decisions, commercial tolerances, etc.

The Calculation of Color Difference Always Sample - (Minus) Standard Différence totale de la couleur dans les coordonnées rectangulaires L* a* b* Échantillon Standard Différence de couleur The Calculation of Color Difference Always Sample - (Minus) Standard The resulting color differences, often referred to as Deltas, (’s) may have descriptive words added to help in their understanding : If L* is +, then sample is lighter If L* is -, then sample is darker If a* is +, then sample is redder (or less green) If a* is -, then sample is greener (or less red) If b* is +, then sample is yellower (or less blue) If b* is -, then sample is bluer (or less yellow) Always remember, the descriptions are primarily used to indicate the direction of change in CIELAB color space and may or may not be discernable. L* = 75.7 a* = +4.1 b* = +87.6 L* = 71.6 a* = +6.9 b* = +78.7

Différence totale des couleurs dans les coordonnées rectangulaires Échantillon De couleur Échantillon De couleur One Number Intended to Work for Pass/Fail Type Decisions An example of why DE*(or the older DE) is not always reliable. The first example illustrates a case where the particular standard/sample pair is judged to be acceptable. Couleur standard Couleur standard The second example illustrates a hypothetical case where the product was rejected because the color difference was concentrated in the “a” value instead of being spread out evenly over all three components in the previous case . Although some of the earlier methods for specification of total color difference, such as the Judd-Hunter (NBS), based on maximum acceptable color differences, and the McAdam and FMC, or FMCII based on minimum perceptible color differences, neither are even mentioned in the current CIE recommendation. (CIE Publication 15.2, 1986).

Problèmes potentiels avec E*

Gamme typique de tolérance industrielle Interprétation des différences de couleur 10 5.0 2.0 CIE LAB Unitès Gamme typique de tolérance industrielle 1.0 0.5 What is the meaning of the color difference numbers? Approximately 0.2 - 0.3 is the threshold of human perception of a just barely noticeable difference. This varies widely, however, with the level of sample lightness, person making the judgment, lighting/viewing conditions, etc. Notice the wide range of industrial tolerances. These depend heavily upon the physical characteristics of the specimens involved (surface smoothness, color, uniformity, texture, etc.) and the end-use requirements. As a general rule, the more smooth the surface and the more uniform the color (such as many paints and plastics), the industrial tolerances are usually at the lower end of the indicated range. When the surface has texture and the color is somewhat naturally non-uniform (such as floor carpet, some building materials and many food products) the tolerances are generally much larger. The size of the samples also play a significant role in the magnitude of allowable differences. In most cases the smaller the samples being compared, the larger the tolerance becomes. Limite visuelle approximative 0.2 0.01 Limite instrumentale

L* = 64.79 a* = 32.21 b* = 83.43 L* = 64.78 C*ab = 89.43 hab = 68.89º L*Blanc Jaune +b* Vert -a* C*ab hab Rouge +a* CIE L* C* h is a polar representation of the CIE L*a*b* rectangular coordinate scale. The CIE L*C*h scale uses CIE L*a*b* to calculate chroma (C*ab) and the hue angle (hab) as follows: For the orange sample, the 10º Observer/D65 CIE L*C*h values are: Bleu -b* L* Noir

Teintes de l’angle CIE (hab) h = arctan +b* 90º b* a* -a* 180º +a* 0º Hue Angle Calculated from to a*,b* Coordinates CIE 1976 a,b hue-angle hab = arctan (b*/a*) = tan-1 (b*/a*) -b* 270º

Amélioration de la tolérance avec les coordonnées  L*  C*  H* Most actual volumes of color match “acceptability” are not rectangular or “box” shaped, but rather are ellipsoid. The polar ∆L* C* H* color space represents a better fit to what are visually acceptable samples. However, notice there are still areas within the polar ∆L* C* H* color difference space where a visually unacceptable sample would fit within the volume and therefore pass the specification. Produits standards Comparaison acceptable

Phénomène par lequel une paire de produits Métamérisme Phénomène par lequel une paire de produits spectralement différents s'assortissent au-dessous d’un ensemble de conditions visuelles, mais pas sous d’autres.

Contraste simultané 1

Contraste simultané 2

Contraste simultané 3

Contraste de clarté simultané

Métamérisme

Qu’est-ce que le métamérisme Plaque standard Plaque standard Échantillon Échantillon 物体の色は、照明光源の違いによって、いろいろと変化して見えます。 例えば、「蛍光灯の室内で同じ色に見えていた２つの試料が、太陽の光の下で見ると違う色に見える」という場合があります。 このような現象をメタメリズム（条件等色）といい、着色剤の種類が異なると起りやすくなります。 Même couleur Couleur différente L'échantillon peut sembler différent de la norme sous une source lumineuse différente.

Illumination Ultra Violet Fluorescence Illumination du jour Illumination Ultra Violet

Fluorescence

Outdoor Exposure Test Site Here is an example of various Paints, coatings, and other products under-going natural weathering tests in South Florida. If you are a manufacturer of these products, and you want to guarantee that the products will not change over a prolonged period of time, testing is mandatory. This is one area where DE* is a typical unit of specification, although the DL* C* H* components would still provide the user with better and more complete information about the fade characteristics.

- Rayons UV - Condensation - Lumière du soleil - Jet de sel - Humidité Instruments pour mesurer les effets de la température et les effets des conditions climatiques Par exemple: - Rayons UV - Condensation - Lumière du soleil - Jet de sel - Humidité

Le choix du papier affecte la couleur de l’encre

Visually Evaluating Appearance under a Non-Standard Condition • North Facing Window • Specimens physically touching each other (no separation) • Uncluttered, neutral surround • Evaluating color - Eye must avoid the specular reflection One major problem - the source of light - is it constant? It will change with time of day and weather conditions. 45°/ 0°

Tests sur la vision des couleurs

Commercially available light inspection booths. • A more consistent source of light. Be sure to follow the manufacturers’ recommendation on lamp replacement after a specified number of hours. • Usually have simulated daylight (D65, D50 or D75) tungsten (A) and cool white fluorescent (F2). Some are also equipped with the custom commercial lamps like Philips TL84 and Ultralume 30U.

La cabine à lumière est un outil qui devrait être utilisé pour les mesures visuelles standardisées angle de l’illumination ? angle de vision ? qualité de lumière ? niveau d’illumination ? arrière-plan ? encadrement ? position du spécimen ?

incandescente & fluorescente. Les 3 sources de lumière les plus communes sont la lumière du jour, incandescente & fluorescente.

450 / 00 Géométrie Source De Lumière Détecteur Échantillon

Intégration de la sphère géométrique sphere Exclusion Du port spéculaire Spécimen au port de réflectivité À la sonde lamp

Instruments portables de contrôle de couleurs: Production

Spectrophotomètres Permets les mesures de métamérisme Contrôle de la composante UV Logiciel pour assortir les couleurs La grandeur du port pour la vision peut être ajusté