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Color Science Color Vision and Color Specification Systems Mechanism of color vision, Chemistry of color vision, Color specification and terminology, Munsell color system Color system using additive color mixing, 1 Color Science Mechanism of Color Vision Unwelcomed mechanisms * Existence of about 100 types of photoreceptors (not accepted) * Presence of six or seven types of photoreceptors Most accepted mechanisms * Trichromtic theory presented by Thomas Young and Hermann von Helmholtz * Opponent color theory presented by Ewald Hering 2 Color Science Young – Helmholtz Theory Three types of photoreceptors named cones, sense red, green and blue colors The degree of response of cone is important issue Advantage? 3 Color Science Hering Theory Three types of photoreceptors which respond to white-black, red-green and yellow-blue opponencies Colors are characterized by the degree of response of these photoreceptors Opponent colors White and Black Red and Green Yellow and Blue 4 Color Science Color Vision Model Stage theories: Trichromatic + opponent theories 5 Color Science Chemistry of Color Vision Eye response and photography, Rhodopsin (purple pigment) in rods Idopsin (Violet pigment) in cones 6 Color Science Color Specification One color different names? Subjective data 7 Color Science Color Specification Systems * Color appearance or perceptual systems (Munsell) * Color mixing systems (CIE) 8 Color Science Color Appearance Systems Based on color perception, Standard materials Psychological impression (subjective) Specified attributes are perceived color Extendable to higher levels of sensory such as texture 9 Color Science Color Mixing Systems Base on the amounts of mixed colored light necessary to obtain a color match to a test color in a color mixing experiments 10 Color Science General Concepts and Comparison between Color Mixing and Color Appearance Systems Color Mixing System Color Appearance System Category Psychophysical color Perceived color Basis Color sensation Color perception Principal Color mixing of light Color appearance of material standards (e.g. color chips) Object of expression Color of light Color of object Typical Example CIE Munsell Specification Values Colorimetric values (e.g Color appearance values (e.g. tristimulus values) hue, lightness, chroma) Process for Color Converting color stimulus Visual color matching with Expression function into psychophysical material standard or values using color matching converting from colorimetric function values 11 Color Science Classification of Samples in Color Appearance System Hue: different colors such as red, blue, .. Lightness: difference between bright violet and dark violet or grays with different lightness Chroma: difference between a yellowish gray and yellow with same lightness 12 Color Science Color Appearance Systems Color appearance values? How many color appearance values? A standard color appearance system? 13 Color Science Differences between Brightness and Lightness? Brightness and the light sources, Lightness and objects What about illuminance? 14 Color Science Color Mixing System Color sensation and, Color stimulus Same responses for matched colors 15 Color Science Color Mixing System Same responses for matched colors 16 Color Science Color Mixing System * Can actual reference stimuli match all colors? * If yes, the color stimulus can be expressed by the amounts of reference stimuli * Amounts are called tristimulus values 17 Color Science Munsell Color System The most attractive color specification system base on the color appearance model Different perspectives 18 Color Science Different Perspectives 19 Color Science Coordinates in Munsell Space Munsell Hue Munsell Value Munsell Chroma However, (Don't forget HV/C) 20 Color Science Munsell Hue RED YELLOW GREEN BLUE PURPLE YR GY BG PB RP 10 basic hues which could be also divided to subgroups 21 Color Science Munsell Value V=0 (ideal black) to V=10 (ideal white) 22 Color Science Munsell Chroma From a gray with equal Munsell Value to as pure as possible colors (open direction) 23 Color Science Munsell Color Solid Is not ideally a sphere 24 Color Science Munsell Chips Are Available Schematically (for educational purpose) Atlas and book Cards 25 Color Science Munsell Notation of Samples Could be determined by visual matching of sample with Munsell chips. Interpolation between neighborhood chips would be possible Munsell notation Don't forget H V/C system e.g., skin color 1.6YR 6.3/3.9 Munsell notation for achromatic colors (white, grays and black) e.g. N3, N 6, N 8 26 Color Science Conditions for Determination of Munsell Codes of Samples Important factors are: Type of light source, Viewing condition, Backgrounds 27 Color Science Advantages of Munsell Color System * Reasonable color position, * Uniform color differences, * Unlimited boundary Disadvantages of Munsell Color System * Inconvenience for some application, * Inaccuracy due to interpolation, * Extrapolation for saturated samples 28 Color Science Additive Color Mixing System R, G and B primary lights Color matching experiment 29 Color Science Typical Primaries in Color Matching Experiment 30 Color Science Color Equation [F1]=[F2] and [F3]=[F4] = signs shows that left-hand side stimulus matches right-hand side stimulus 31 Color Science Grassman Laws for Additive Mixtures Proportionality: α[F1]=α[F2] and α[F3]=α[F4], Additivity: [F1]+[F3]=[F2]+[F4] and [F1]+[F4]=[F2]+[F3], 32 Color Science General Form of Color Equation [F]=R[R]+G[G]+B[B] * Values of R, G and B depends on the type of [R], [G] and [B] * [R], [G] and [B] should be standard to compare the results of color matching experiments 33 Color Science So, Two Critical Points Should Be Answered Colorimetric values of[R], [G] and [B], The relative values of the luminances of each primary, i.e. R, G and B 34 Color Science Primary Stimuli, or Reference Color Stimuli? Tristimulus values The value of each primary i.e. R, G and B in color equation 35 Color Science Matching of Monochromatic Light Sources The rλ , gλ and bλ are the amounts of [R], [G] and [B] primary stimuli which match the spectral light source [Fλ] 36 Color Science Tristimulus Values of Polychromatic Stimulus If two monochromatic lamps [Fλ1] f1[Fλ1 ] = f1 (rλ1[R ] + g λ1[R ] + bλ1[B]) and [Fλ2], f 2 [Fλ 2 ] = f 2 (rλ 2 [R ] + g λ 2 [R ] + bλ 2 [B]) match the color[F] 37 Color Science In Mathematical Form: [F] = f1[Fλ1 ] + f 2 [Fλ 2 ] = f1 (rλ1[R ] + gλ1[R ] + bλ1[B]) + f 2 (rλ 2 [R ] + g λ 2 [R ] + bλ 2 [B]) = (f1rλ1 + f 2 rλ 2 )[R ] + (f1g λ1 + f 2 g λ 2 )[G ] + (f b 1 λ1 + f 2 bλ 2 )[B] 38 Color Science The Tristimulus Values of Stimulus [F] R = (f1rλ1 + f 2 rλ 2 ) G = (f1g λ1 + f 2 g λ 2 ) B = (f1bλ1 + f 2 bλ 2 ) In the Case of n Monochromatic Lights: n R = ∑ f i rλi i =1 n G = ∑ f i g λi and i =1 n B = ∑ f i bλi i =1 39 Color Science Replacement of Radiant Power with Spectral Power Distribution P(λ) n R = ∑ P(λ )rλi Δλ i =1 n G = ∑ P(λ )gλi Δλ i =1 n B = ∑ P (λ )rλ i Δ λ i =1 40 Color Science Change the Summation with Integral R= ∫ P(λ )r(λ )dλ vis G= ∫ P(λ )g (λ )dλ vis B= ∫ P(λ )b(λ )dλ vis 41 Color Science Tristimulus Values of Object Colors R= ∫ P(λ )R(λ )r (λ )dλ vis G= ∫ P(λ )R(λ )g (λ )dλ vis B= ∫ P(λ )R(λ )b (λ )dλ vis 42 Color Science The most important additive color mixing system is CIEXYZ which defines its primaries in a manner that match all actual colors with the non-negative values of its imaginary primaries 43
"Color Vision and Color Specification Systems"