The Principles of Chromatics 03/20/07 2 Light Electromagnetic radiation, that produces a sight perception when being hit directly in the eye The wavelength of visible light is 400-700 nm 1
03/20/07 3 Visible Light 03/20/07 4 The prism divides the light into its different wavelength components 2
03/20/07 5 Color Subjective impression Different wavelengths cause different color perceptions The short cause blue and the long cause red 400 700 nm 03/20/07 Group discussion 1 Which things have an effect to perceiving a color? 3
03/20/07 7 The Perception of Color You need three elements to perceive colors LIGHT wavelength intensity direction TARGET Selective reflection wavelength intensity direction PERCEIVER Color stimuli physiological color perception Psychological color perception 03/20/07 8 The Color of an Object The color effect caused by the light that the object emits Kuva:Creo 4
03/20/07 9 Target Color Stimulus The 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 10 History Newton, 1666 Realised that the sun light consists of the different colors of the spectre Laid the ground for the current chromatics and color reproduction Christoffel Leblon, 1722 Tri-color principle Maxwell, 1861 The first color photograph 5
03/20/07 11 The Eye's Color Vision Part of the light travels to the retina where light sensitive cells react to the light stimulus by transferring the stimuluslike signal from retina to the brain Retina has two kinds of cells that react to the light stimulus 03/20/07 12 Kuva:Agfa 6
03/20/07 13 Retina has two kinds of cells that react to the light stimulus ROD CELLS Distinguishes the differences in lightness RETINAL CONES - cones; different spectral sensitiveness Color vision 03/20/07 14 Color sensitive retinal cone 7
03/20/07 15 Kuva:Agfa 03/20/07 16 Spectral sensitivities of retinal cones 8
03/20/07 17 Contributing factors of Color perception Memory Background color and brightness Adaptation of the eyes Lighting diffusion/direct lighting Color surface area 03/20/07 18 Effects of background colors 9
03/20/07 19 03/20/07 20 10
03/20/07 21 Color temperature Light is characterized as color temperature The temperature of an ideal radiator radiating a specific colored light (black-body, Planck radiator) Presented as Kelvin-degrees (K) ; Kelvin = o C +273 03/20/07 22 - As the temperature changes the level of radiation energy and its spectral distribution (color) changes 11
03/20/07 23 Color Temperature The 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-degrees candlelight ~ 2000 o K blue sky 12 000-18 000 o K daylight ~ 5000 o K 03/20/07 24 Color temperatures of the CIE standard ligth sources A 2800 o K ( tungsten lamp) B 4900 o K ( sun) C 6700 o K ( northern sky) D 65 6500 o K ( northern sky + UV) D 50 5000 o K ( white light, gas lamp) 12
03/20/07 25 Spectral remission figures of standard light sources 03/20/07 26 Metameria Two colors, with different spectral remission curves may look similar Two colors may look similar in one lighting and totally different in another 13
03/20/07 27 Chromatic colors Colorful colors Colors with tone 03/20/07 28 Achromatic colors Black, white, gray Neutral colors No tone 14
03/20/07 29 The reflection spectre of color spectral sensitivity distribution of light reflected from a lighted surface 03/20/07 30 Color models, representations of color Visual color The technical representation of color additive color formation subtractive color formation Colorimetric color definition Indexed color representation Color maps 15
03/20/07 Group discussion 2 What color systems you know? 03/20/07 32 Visual color psychophysical, subjective impression The human eye senses the color of electromagnetic radiation depending on its wavelength Short wavelengths as blue, long as red 16
03/20/07 33 additive Additive Color Formation The desired color is generated by mixing lights of different colors The starting point is black; red, green and blue color is added to get white Primary colors R,G,B Secondary colors C,M,Y In TV-and computer monitors 03/20/07 34 The additive color mixing 17
03/20/07 35 Color formation in the monitor: -additive - R,G,B-phosphors Kuva : Agfa 03/20/07 36 Additive color specification in Photoshop 18
03/20/07 37 RGB-primary color numerical figures Red 255,0,0 Green 0,255,0 Blue 0,0,255 03/20/07 38 Subtractive Color Formation subtractive The starting point is white subtracting red,green, blue to get black Subtraction with filters that are printing ink layers Filtering is made with pigments which are the opposite colors of the filtered colors Primary colors cyan, magenta and yellow 19
03/20/07 39 The starting point in substractive color formation is white 03/20/07 40 Kuva:Creo 20
03/20/07 Group discussion 3 What 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 42 Subtractive color formation cyan magenta yellow black 21
03/20/07 43 Subtractive color mixing 03/20/07 44 Subtractive color specification in Photoshop 22
03/20/07 45 The Numerical Values of CMYK- Primary Colors RGB CMYK 0,255,255 100,0,0,0 255,0,255 0,100,0,0 255,255,0 0,0,100,0 0,0,0 0,0,0,100 03/20/07 46 Colorimetric color definition Tries to define the color as the eye perceives it components HUE SATURATION LIGHTNESS 23
03/20/07 47 The Colorimetric components of Color HUE impression of color the name of color SATURATION the intensity of color purity 0 on gray, white and black LIGHTNESS total reflection high with white and yellow colors low with black 03/20/07 48 Visual scales of Hue, Saturation and Luminance - components of color Hue Saturation Luminance 24
03/20/07 49 Selecting colors using the HSL color model in Adobe Photoshop Munsell's color system 1915 (brightness) 5 primary tones: red (R),yellow (Y), green (G),blue (B), purple (P) Complementary tones: YR,GY,BG,PB,RP 03/20/07 Each tone has a numerical value 10-100, lightness (value) 10-100 % 50 Pure color saturation (chroma) 10-15, with acromatic colors 0 25
03/20/07 51 CIE-color definition International standard 1931,1964 Mathematical way to define the colorimetrical components The goal is a device-independent color definition CIEXYZ Is measured with tristimuli filters that match the eye's color sensitivity Reflection values X,Y,Z Counting color coordinates x,y 03/20/07 52 CIEXYZ color model Looking for corresponding reference color R,G,Blight mixes Color mix curves Primary stimuli R,G,B is replaced with X, Y, Z virtual stimuli (> color mix curves give positive figures) 26
03/20/07 53 Standard Observer 2 o viewing angle (in the definition from 1934) 10 o viewing angle (from 1964) 03/20/07 54 CIE chromaticity diagram X,Y,Z: standard tristimuli values Counting the color coordinates x,y,z x= X/(X+Y+Z) y=y/(x+y+z) z=z/(x+y+z) 27
03/20/07 55 CIE Chromaticity diagram x=y=0.333= neutral, achromatical point Colour tone is read from the sphere of the cross-section figure = dominating wavelength Saturation = stimulus purity ( the relative distance from the neutral point) Y=lightness 03/20/07 56 28
03/20/07 57 The colorimetrical parameters in a CIEXYZ-diagram Color tone Saturation Lightness Dominating wavelength, nm Stimulus purity % Y-value Kuva : Agfa 03/20/07 58 29
03/20/07 59 Kuva : Agfa 03/20/07 60 CIELab Mathematical conversion from CIEXYZ parameters L = lightness a = chromaticity in red-green-axis b = chromaticity in yellow-blue- axis 30
03/20/07 61 CIELab L = 116 (Y/Y 0 ) 1/2-16 a* = 500 ((X/X0) 1/3 - (Y/Y0)) 1/3 b* = 200 ((Y/Y 0 ) 1/3 -(Z/Z 0 )) 1/3 X 0,Y 0,Z 0 = tristimulus values of white light 03/20/07 62 31
03/20/07 63 Lightness Saturation Hue 03/20/07 64 Color hue ( hue angle ) and saturation ( chroma) in CIELab-coordinate 32
03/20/07 65 CIELab-color system's a- and b- coordinates' placing in x,ycoordinates 03/20/07 66 Lab Color specification in Photoshop 33
03/20/07 67 Color difference E Color difference: E = ( a*) 2 + ( b*) 2 + ( L* ) 2 03/20/07 68 The Difference Between Color hues Color difference: E = ( a*) 2 + ( b*) 2 + ( L* ) 2 E < 1 E = 2 E > 3 The difference isn't noticeable in viewing conditions The difference is noticeable to an experienced observer Clear difference 34
03/20/07 69 IFRA Quality Club L*a*b* - specifications for newspapers L* a* b* cyan 57.00-23.00-27.00 magenta 53.00 48.00 0.00 yellow 79.00-5.00 58.00 red 52.00 41.00 25.00 green 53.00-34.00 18.00 blue 41.00 7.00-22.00 color gamut 4334 03/20/07 70 35
03/20/07 71 Exercise: 03/20/07 72 CIELuv-color presentation Derivative from the CIEXYZ-system The intention is to get the distances in the coordinate to match the color differences that the eye sees parameters L,u,v L = luminance, lightness u,v = chromaticity, coloricity The use in additive color systems (e.g TV) 36
03/20/07 73 CIELuv u = 4x /-2x-12y-3 v = 6y /-2x-12y-3 03/20/07 74 YCC color model A color format developed by Kodak to illustrate color in TV- and computer monitors Is used in Kodak's Photo CD-system Luminance component Y Chromaticity components C 1, C 2 37
03/20/07 75 Indexed color presentation The colors are presented with predefined color palette's colors 03/20/07 76 Indexed color specification in Photoshop 38
03/20/07 77 Color Maps The colors are presented with the help of reference map's model colors e.g. PANTONE; Focoltone 03/20/07 78 Pantone Color specification in Photoshop 39