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Color Representation 1931 – the Commission International De L’Eclairage (CIE) Defined a Standard System for Color Representation

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Color Representation 1931 – the Commission International De L’Eclairage (CIE) Defined a Standard System for Color Representation Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. CIEXYZ Lecture 3 Color Coordinate System Color Representation 1931 – The Commission International de l’Eclairage (CIE) Defined a standard system for color representation. CIEXYZ Color Space CIE Chromaticity Space HSL,HSV,LUV,CIELab The CIE-XYZ Color Coordinate System. Y In this system, the XYZ Tristimulus values can describe any visible color. The XYZ system is based on the color matching experiments X Z Trichromatic Color Theory Calculating the CIEXYZ Color Coordinate System “tri”=three “chroma”=color CIE-RGB Every color can be represented by 3 values. 3 r(l) 80 2 60 e1 40 b(l) g(l) 1 e2 20 e3 IntensityPrimary 0 400 500 600 700 0 Wavelength (nm) 400 500 600 700 Wavelength (nm) Space of visible colors is 3 Dimensional. David Wright 1928-1929, 1929-1930 & John Guild 1931 17 observers responses to Monochromatic lights between 400- 700nm using viewing field of 2 deg angular subtense. Primaries are monochromatic : 435.8 546.1 700 nm 2 deg field. These were defined as CIE-RGB primaries and CMF. XYZ are a linear transformation away from the observed data. Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. CIEXYZ Luminous-Efficiency function of Color Coordinate System the human eye CIE Criteria for choosing Primaries X,Y,Z and Color Matching Functions x,y,z. 1 1) CMFs are non-negative over visible wavelengths. (i.e. any color is represented by 3 positive values). 0.6 2) Equal amounts of the Primaries produce white. (i.e. X=Y=Z for stimulus of equal luminance at each wavelength). 0.2 Luminous Efficiency 3) The y color matching function is defined to match 400 500 600 700 the luminous-efficiency function of the human eye. Wavelength (nm) 4) Primaries are as ‘tight’ as possible around the set of possible colors (Maxwell triangle Projects to equilateral in XYZ space). CIEXYZ CIE-RGB to CIE-XYZ Color Coordinate System Y X Z CIE-RGB Chromaticity space (rg). * Cr, Cg, Cb must enclose the Gamut. * Line Cb-Cr is defined by Y being Luminance Function. (the Alychne = line of zero luminance). * Line Cr-Cg is tangent at 650+ (z is zero beyond 650). * Thus Cr is defined. * Equal Energy (x=y=z=1/3) puts constraint on Cb-Cg * Tight around Gamut -> line Cb-Cg is close to green. * Cb and Cg are defined. Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. CIE-RGB to CIE-XYZ CIE Color Standard - 1931 CIE RGB space to XYZ space. 1.8 Map Cb Cg Cr to x=(0,0) y=(0,1) z=(1,0) 1.4 z(l) 1 y(l) x(l) 0.6 Tristimulus values 0.2 400 500 600 700 Wavelength (nm) • y is predefined. • Non negative over the visible wavelengths. (X,Z – Several Hundreds, Y – 0..100). • The 3 primaries associated with x y z color matching functions are unrealizable (negative power in some of the wavelengths). • Integral over the CMF gives equal values. • CMF are linear transformation away from CIE-RGB and from LMS. CIE Color Standard - 1964 Colorimeters Stiles and Birch data (1959): Color Matching Experiment with: 10 Deg view Primaries: 444.4 525.3 645.2 CIE-XYZ10 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Color matching functions vs LMS - cone photoreceptor responses CIE – RGB Primaries are monochromatic : 435.8 546.1 700 nm XYZ Tristimulus System Cone Spectral Sensitivity 1.8 1 x(l) L 1.4 y(l) M S z(l) 0.75 X 1.9023 -1.4000 0.3544 R 1 Y = 0.6371 0.3933 -0.0093 G 0.5 B 0.6 Z 0.0007 0.0033 1.7462 Tristimulus values 0.25 Relative sensitivity Relative 0.2 0 400 500 600 700 400 500 600 700 Wavelength (nm) Wavelength (nm) The cone responses form a 3D linear system. Cone responses are equivalent for metamers. thus The cone spectral sensitivities and the XYZ color matching functions are related by a 3 x 3 linear transformation. X 1.9023 -1.4000 0.3544 L Y = 0.6371 0.3933 -0.0093 M Z 0.0007 0.0033 1.7462 S CIEXYZ CIEXYZ Color Coordinate System Color Coordinate System x y z Color Matching Functions Y 1.8 1.4 z(l) y(l) 1 x(l) X 0.6 Tristimulus values 0.2 400 500 600 700 Wavelength (nm) Z Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. CIE Chromaticity Diagram CIE Chromaticity Diagram X X = x X+Y+Z Y Y = y 0.9 X+Y+Z Y 520 Z 530 Z = z X+Y+Z (ax,ay,az) 510 540 550 x+y+z = 1 y 505 560 570 500 X 0.5 580 495 590 600 610 490 650 485 Z 480 470 0.0 450 0.50.0 1.0 x A common representative of color signal: [x,y,Y] Color Naming CIE-RGB Primaries 0.9 520 530 510 540 550 505 green 560 570 500 yellow- green 0.5 580 y yellow 590 495 orange 600 white 610 490 cyan pink red 650 485 magenta blue 480 purple 470 450 0.0 0.5 1.0 x Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Blackbody Radiators and Blackbody Radiators CIE standard Illuminants CIE Standard Illuminants: A - tungsten light B - Sunset 3000K C - blue sky D65 - Average daylight E - Equal energy white (x=y=z=1/3) 3500K 0.8 Relative energyRelative 0.6 9000K 4000 5000 3000 y 6000 2000 0.4 7000 Wavelength (nm) 8000 A 10000 B 20000 C E 0.2 D65 0 0 0.2 0.4 0.6 0.8 x http://www.olympusmicro.com/primer/java/colortemperature/index.html Television Primaries and Gamut Signal Lights R 1 G 1 B 1 - Primaries used for PAL R 2 G 2 B 2 - Primaries used for NTSC D65 - reference white for PAL C - reference white for NTSC 0.8 G NTSC 2 PAL 0.6 G1 y 0.4 D65 R1 E R2 C 0.2 B1 B 0 2 0 0.2 0.4 0.6 0.8 x CIE Chromaticity + Gamut applet : http://www.cs.rit.edu/~ncs/color/a_chroma.html Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Chromaticity in Polar Coordinates XYZ Color Space Given a reference white. Hue vs Saturation Dominant Wavelength – wavelength of the spectral color which added to the reference white, produces the given color. 0.8 550 0.6 0.4 490 630 Reference white 0.2 0 0 0.2 0.4 0.6 0.8 Chromaticity in Polar Coordinates Chromaticity in Polar Coordinates Given a reference white. Given a reference white. Complementary Wavelength – Purity – wavelength of the spectral color which added the ratio of the lengths between the given color and to the given color, produces the reference white. reference white and between the dominant wavelength and reference white. Ranges between 0 .. 1. 0.8 0.8 0.6 570 0.6 0.2 0.4 0.4 485 Reference Reference white white 0.2 0.2 0.4 0 0 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. EXAMPLE: Chromaticity in Polar Coordinates Reference white is CIE standard illuminant - C. Dominant Wavelength of color S1 is D1 of color S2 is D2. 0.8 Complementary Wavelength of color S1 is‘ D1. S2 does not have a complimentary wavelength. Dominant/complimentary 0.6 Wavelength Excitation Purity of S is the ratio CS /CD 1 1 1 Y of S2 is the ratio CS2/CD2 0.4 purity of S3 is the ratio CS3/CD3 reference white 0.8 D2 0.2 0.6 0 S2 0 0.2 0.4 0.6 0.8 S X 0.4 D1 S1 C D1‘ 0.2 S3 D3 0 0 0.2 0.4 0.6 0.8 Color Description Munsell Color System (1915) Hue (red, green, yelow, blue ...) Equal perceptual steps in Hue Saturation Value. Saturation (pink,bright red, ....) Hue: R, YR, Y, GY, G, BG, B, PB, P, RP (each subdivided into 10) Chroma: 0 ... 20 (neutral ... saturated) Lightness (black, grey, white ....) Value: i0 ... 10 (dark ... pure white) (Value) 10/ White 5/ Value 10R 5R 5YR 10YR /10 10RP 1/ /6 /8 /2 /4 5RP 5Y G Hue R Saturation 10P 10Y B 5P 5GY /2 10PB 10GY Brightness /4 5PB /6 5G Example: 10B /8 5YR 8/4 /10 10G 5B 5GB Black 10GB Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Munsell Book of Colors Color Polytopes Applets: http://www.cs.rit.edu/~ncs/color/a_spaces.html Atlas of thr Munsell Color System (1915) http://www.nacs.uci.edu/~wiedeman/cspace/me/rgbhsv.html MayuraDraw PowerPoint Generated by Foxit PDF Creator © Foxit Software http://www.foxitsoftware.com For evaluation only. Photoshop Color Picker Color Space Summary Spectral Power Distribution (SPD) – High Dimensional 3 Dimensional Spaces: LMS - Human Cone responses. Given by the cone sensitivity curves. CIE–RGB - Based on color Matching Experiments by Wright+Guild. Defined by Primaries R G B (monochromatic 435.8 546.1 700 nm) and cmf r g b. CIE-XYZ - Standard Color space. Linear transformation of above that confirms to set of constraints.
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