Coor and Coor Mode Chap. 12
Coor Visibiity n Interpretation of coor is a psychophysioogy probem We coud not fuy understand the mechanism Physica characteristics of coor can be represented by a forma expression presentation by experimenta resuts n The concept of coor Spectrum of coor : discovered in 1666 by Newton Newton s prism decomposition
Physics of Light n Eectromagnetic spectrum: n Visibe spectrum : red 750 nm ~ vioet 380 nm
Physics of Light Some exampes of the refectance spectra of surfaces % Photons Refected Red Yeow Bue Purpe 400 700 400 700 400 700 Waveength nm 400 700 dominant waveength or dominant frequency
Psychoogica Characteristics of Coor Mean Hue # Photons bue green yeow Waveength Hue: indicates a characteristic reated to the dominant waveength in a mixed ight wave, and represents a dominant coor as perceived by a human observer
Psychoogica Characteristics of Coor Area Brightness B. Area Lightness Stephen E. Pamer, 2002 # Photons bright dark n Luminance Waveength the measured amount of energy perceived by an observer Lumens the physica measure of brightness. Stephen E. Pamer, 2002
Psychoogica Characteristics of Coor Variance Saturation # Photons hi. med. ow high medium ow Waveength n Saturation purity Ø Ø How cose a ight appear to be to a pure spectra coor how much a coor is NOT mixed with the white ight Chromacity: hue + saturation Stephen E. Pamer, 2002
Intensity & Brightness 300 700 200 100 700 400 400 400 400 500 300 600 600 600 300 intensity 4 3 2 1 Spectrum 100 200 300 400 500 600 700nm intensity : the amount of ight, or the amount of a particuar coor actuay refected or transmitted from a physica object. brightness : measured intensity after it is acquired, samped, and observed with our eyes
Coor Modes n Coor Mode Any method for expaining the properties or behavior of coor within some particuar context n No singe coor mode can expain a aspects of coor n Use different modes to hep describe different coor characteristics
Primary Coors n Combine the ight from two or more sources with different dominant frequencies Varying the amount intensity of ight from each source Þ a range of additiona coors n Primary coors Hues for the sources n Coor gamut for the mode The set of coors which can be produced from the primary coors n Compementary coor Two primaries that produce white
Primary Coors of Light n Red, Green, Bue n Why we choose these three Among 6-7 miion cone ces of our eye, 65% is sensitive to red 630 nm: L cones 33% is sensitive to green 530 nm: M cones 2% is sensitive to bue 450 nm: S cones
Coor Matching Function n Tri-stimuus è the amount of R, G, B ights to form a certain coor C = r R + g G + b B n From the coor matching experiment Conducted by W. David Wright and John Guid in the 1920s
Coor Matching Experiment 1
Coor Matching Experiment 1 R: 700.0 nm G: 546.1 nm B: 435.8 nm R G B
Coor Matching Experiment 1 R: 700.0 nm G: 546.1 nm B: 435.8 nm R G B
Coor Matching Experiment 1 The primary coor amounts needed for a match R G B
Coor Matching Experiment 2
Coor Matching Experiment 2 R: 700.0 nm G: 546.1 nm B: 435.8 nm R G B
Coor Matching Experiment 2 R: 700.0 nm G: 546.1 nm B: 435.8 nm R G B
Coor Matching Experiment 2 We say a negative amount of R was needed to make the match, because we added it to the test coor s side. The primary coor amounts needed for a match: R G B R G B R G B
CIERGB Coor System n A coor system pubished in 1931 by CIE, Internationa Commission on Iumination n Based on experimenta resuts n When we use R,G,B coor, we have negative primaries CIERGB Coor Matching Functions
CIERGB Coor System CIERGB Coor System b g r b b b g r g g b g r r r + + = + + = + + = rg Chromacity Diagram Normaize
CIEXYZ Coor Space n The dominant internationa standard for coor specification 1931, by CIE n Use three imaginary primary coors, X, Y, and Z n The foowing transformation [Dean B. Judd] makes coor matching functions positive everywhere x = 2.7689r + 1.7517g + 1.1302b y = 1.0000r + 4.5907g + 0.0601b z = 0.0000r + 0.0565g + 5.5943b
CIEXYZ Coor Space
A rea coors can be represented as positive combinations of x, y since x+y+z=1 CIEXYZ Coor Space CIEXYZ Coor Space z y x z z z y x y y z y x x x + + = + + = + + = Normaize
CIEXYZ Coor Space n CIE chromaticity diagram encompasses a the perceivabe coors in 2D space x,y
CIEXYZ Coor Space n CIExyY Coor Space Y: uminance factor or uminance refectance x y z X = = = : reated to brightness = X X + Y + Z Y X + Y + Z Z X + Y + Z x y Y, Z = z y Y e.g.1 X=10, Y=20, Z=30 10 10 x = = = 0.167 10 + 20 + 30 60 20 20 y = = = 0.333 10 + 20 + 30 60 e.g.2 X=20, Y=40, Z=60 20 20 x = = = 0.167 20 + 40 + 60 120 20 40 y = = = 0.333 20 + 40 + 60 120
CIE Chromacity Diagram n n n Spectra coors pure coors Iuminant, C White-ight position Standard approximation for average dayight Luminance vaues not avaiabe n The chromacity diagram is usefu for: Comparing coor gamuts for different sets of primaries. Identifying compementary coors Determining purity and dominant waveength for a given coor
CIE Chromacity Diagram n Coor gamut a set of coors a coor mode can describe Coor gamut for three points: a triange with vertices at the three coor positions n No triange within the diagram can encompass a coors!
CIE Chromacity Diagram n Compementary coors : together produce white coor. n Iuminant C average dayight
CIE Chromacity Diagram n Dominant waveength : hue A straight ine from C through that coor point to a spectra coor on the chromacity diagram C 1 & C s C 1 : C s mixed with white ight C The dominant coor of C 2 is C sp C 2 has spectra distribution with subtractive dominant waveength n Purity : saturation represnted as the ratio of distances = d / d Purity of C 1 c 1 cs
RGB Coor Mode Red, Green, Bue ights: additive mode Used in video monitor dispays C = R, G, B = RR + GG + BB Gray scae
Cyan, Magenta, Yeow Subtractive mode Used in hard-copy devices such as printer and potter CMYK coor mode - K for back ink for reducing the amount of ink CMY Coor Mode CMY Coor Mode ú ú ú û ù ê ê ê ë é - ú ú ú û ù ê ê ê ë é = ú ú ú û ù ê ê ê ë é Y M C B G R 1 1 1 ú ú ú û ù ê ê ê ë é - ú ú ú û ù ê ê ê ë é = ú ú ú û ù ê ê ê ë é B G R Y M C 1 1 1
CMYK Exampe
HSV Coor Mode n hue H, saturation S, and vaue V pure hues: V=1.0, S=1.0 white point: V=1.0, S=0
HSV Coor Mode n Shades Adding back decreases V aong the side of the hexcone toward the back point S=1.0, 0.0 V 1.0 n Tints Adding white decreases S across the top pane of the hexcone V=1.0, 0.0 S 1.0 n Tones Adding both back and white about 128 different hues about 130 different tints about 23 shades for yeow about 16 shades for bue We can distinguish 128 130 23=382,720 coors
HSL Coor Mode u u Hue H, saturation S, ightness L, Hue & Saturation give a chromatic information Hue: [0,360] Saturation, Intensity : [0,1]