The Principles of Chromatics

LightElectromagnetic radiation, that produces a sight perception when being hit directly in the eyeThe wavelength of visible light is 400 - 700 nm03/20/07*

Visible Light03/20/07*

03/20/07*The prism divides the light into its different wavelength components

ColorSubjective impressionDifferent wavelengths cause different color perceptions The short cause blue and the long cause red03/20/07*400700 nm

Group discussion 1Which things have an effect to perceiving a color?03/20/07

The Perception of Color LIGHTwavelengthintensitydirectionTARGETSelective reflectionwavelengthintensitydirection03/20/07*You need three elements to perceive colorsPERCEIVERColor stimuliphysiological color perceptionPsychological color perception

The color effect caused by the light that the object emits03/20/07*The Color of an ObjectKuva:Creo

Target Color StimulusThe color is determined by the stimulus that is directed to the eye that depends on the light source's spectral power peak S ( ) and the target's reflection spectre R ( )03/20/07*

HistoryNewton, 1666Realised that the sun light consists of the different colors of the spectreLaid the ground for the current chromatics and color reproductionChristoffel Leblon, 1722Tri-color principleMaxwell, 1861The first color photograph03/20/07*

The Eye's Color VisionPart of the light travels to the retina where light sensitive cells react to the light stimulus by transferring the stimulus-like signal from retina to the brainRetina has two kinds of cells that react to the light stimulus03/20/07*

03/20/07*Kuva:Agfa

Retina has two kinds of cells that react to the light stimulus

ROD CELLSDistinguishes the differences in lightness

RETINAL CONES- cones; different spectral sensitivenessColor vision

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03/20/07*Color sensitive retinal cone

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Spectral sensitivities of retinal cones03/20/07*

Contributing factors of Color perceptionMemoryBackground color and brightnessAdaptation of the eyesLightingdiffusion/direct lightingColor surface area03/20/07*

Effects of background colors03/20/07*

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Color temperatureLight is characterized as color temperatureThe temperature of an ideal radiator radiating a specific colored light (black-body, Planck radiator)Presented as Kelvin-degrees (K) ; Kelvin = oC +273

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03/20/07* As the temperature changes the level of radiation energy and its spectral distribution (color) changes

Color TemperatureThe color temperature describes the color of the light emitted by the source The color temperature represents the temperature of the emitting black body in K-degreescandlelight ~ 2000 oKblue sky 12 000-18 000 oKdaylight ~ 5000 oK 03/20/07*

Color temperatures of the CIE standard ligth sourcesA 2800 oK ( tungsten lamp)B 4900 oK ( sun)C 6700 oK ( northern sky)D 65 6500 oK ( northern sky + UV)D 50 5000 oK ( white light, gas lamp)03/20/07*

Spectral remission figures of standard light sources 03/20/07*

MetameriaTwo colors, with different spectral remission curves may look similarTwo colors may look similar in one lighting and totally different in another03/20/07*

Chromatic colorsColorful colorsColors with tone03/20/07*

Achromatic colorsBlack, white, grayNeutral colorsNo tone03/20/07*

The reflection spectre of colorspectral sensitivity distribution of light reflected from a lighted surface03/20/07*

Color models, representations of colorVisual colorThe technical representation of coloradditive color formationsubtractive color formationColorimetric color definitionIndexed color representationColor maps03/20/07*

Group discussion 2What color systems you know?03/20/07

Visual colorpsychophysical, subjective impressionThe human eye senses the color of electromagnetic radiation depending on its wavelengthShort wavelengths as blue, long as red03/20/07*

Additive Color FormationadditiveThe desired color is generated by mixing lights of different colors The starting point is black; red, green and blue color is added to get whitePrimary colors R,G,BSecondary colors C,M,YIn TV-and computer monitors03/20/07*

03/20/07*The additive color mixing

03/20/07*Kuva : AgfaColor formation in the monitor:-additive- R,G,B-phosphors

03/20/07*Additive color specification in Photoshop

RGB-primary color numerical figures03/20/07*

Subtractive Color FormationsubtractiveThe starting point is whitesubtracting red,green, blue to get blackSubtraction with filters that are printing ink layersFiltering is made with pigments which are the opposite colors of the filtered colorsPrimary colors cyan, magenta and yellow03/20/07*

The starting point in substractive color formation is white03/20/07*

03/20/07*Kuva:Creo

Group discussion 3What wavelength has to be absorbed in order to produce-yellow?-cyan?

Which pigments have to be combined in order to produce red color?03/20/07

Subtractive color formation03/20/07*

03/20/07*Subtractive color mixing

03/20/07*Subtractive color specification in Photoshop

The Numerical Values of CMYK-Primary Colors03/20/07*RGBCMYK

Colorimetric color definitionTries to define the color as the eye perceives itcomponentsHUESATURATIONLIGHTNESS03/20/07*

The Colorimetric components of ColorHUEimpression of colorthe name of colorSATURATIONthe intensity of colorpurity0 on gray, white and black

LIGHTNESStotal reflectionhigh with white and yellow colorslow with black03/20/07*

03/20/07*Visual scales of Hue, Saturation and Luminance - components of color

03/20/07*Selecting colors using the HSL color model in Adobe Photoshop

03/20/07*Munsell's color system 19155 primary tones: red (R),yellow (Y), green (G),blue (B), purple (P)Complementary tones: YR,GY,BG,PB,RPEach tone has a numerical value 10-100, lightness (value) 10-100 %Pure color saturation (chroma) 10-15, with acromatic colors 0

CIE-color definitionInternational standard 1931,1964Mathematical way to define the colorimetrical componentsThe goal is a device-independent color definition CIEXYZIs measured with tristimuli filters that match the eye's color sensitivity Reflection values X,Y,ZCounting color coordinates x,y03/20/07*

Looking for corresponding reference color R,G,B-light mixesColor mix curvesPrimary stimuli R,G,B is replaced with X, Y, Z virtual stimuli (> color mix curves give positive figures)03/20/07*CIEXYZ color model

Standard Observer2o viewing angle(in the definition from 1934)10o viewing angle (from 1964)

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CIE chromaticity diagram X,Y,Z: standard tristimuli valuesCounting the color coordinates x,y,z x= X/(X+Y+Z)y=Y/(X+Y+Z)z=Z/(X+Y+Z)03/20/07*

x=y=0.333= neutral, achromatical pointColour tone is read from the sphere of the cross-section figure = dominating wavelengthSaturation = stimulus purity ( the relative distance from the neutral point)Y=lightness03/20/07*CIE Chromaticity diagram

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03/20/07*Color toneSaturationLightnessThe colorimetrical parameters in a CIEXYZ-diagramKuva : AgfaDominating wavelength, nmStimulus purity %

Y-value

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03/20/07*Kuva : Agfa

CIELabMathematical conversion from CIEXYZparametersL = lightnessa = chromaticity in red-green-axisb = chromaticity in yellow-blue- axis03/20/07*

CIELabL = 116 (Y/Y0)1/2 -16a* = 500 ((X/X0)1/3 - (Y/Y0))1/3b* = 200 ((Y/Y0)1/3-(Z/Z0))1/3

X0,Y0,Z0 = tristimulus values of white light03/20/07*

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Lightness

Hue

Saturation

03/20/07*Color hue ( hue angle ) and saturation ( chroma) in CIELab-coordinate

03/20/07*CIELab-color system's a- and b-coordinates' placing in x,y-coordinates

03/20/07*Lab Color specification in Photoshop

03/20/07*Color difference EColor difference:E = (a*) 2 + ( b*) 2 + ( L* ) 2

The Difference Between Color hues03/20/07*Color difference:E = (a*) 2 + ( b*) 2 + ( L* ) 2

E < 1 The difference isn't noticeable in viewing conditions

E = 2The difference is noticeable to an experienced observer

E > 3Clear difference

03/20/07*IFRA Quality Club L*a*b* - specifications for newspapersL* a* b*cyan57.00 -23.00 -27.00magenta 53.00 48.00 0.00yellow79.00 - 5.0058.00red 52.00 41.0025.00green53.00 -34.0018.00blue41.00 7.00 -22.00

color gamut 4334

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Color gamut

a

-a

b

-b

03/20/07*Exercise:

CIELuv-color presentationDerivative from the CIEXYZ-systemThe intention is to get the distances in the coordinate to match the color differences that the eye sees parameters L,u,vL = luminance, lightnessu,v = chromaticity, coloricityThe use in additive color systems (e.g TV)

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CIELuv u = 4x /-2x-12y-3 v = 6y /-2x-12y-303/20/07*

03/20/07*YCC color modelA color format developed by Kodak to illustrate color in TV- and computer monitorsIs used in Kodak's Photo CD-systemLuminance component YChromaticity components C1 , C2

Indexed color presentationThe colors are presented with predefined color palette's colors03/20/07*

03/20/07*Indexed color specification in Photoshop

Color MapsThe colors are presented with the help of reference map's model colors e.g. PANTONE; Focoltone03/20/07*

03/20/07*Pantone Color specification in Photoshop

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