Color and Color Model Chap. 12

Transcription

1 Coor and Coor Mode Chap. 12

2 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

3 Physics of Light n Eectromagnetic spectrum: n Visibe spectrum : red 750 nm ~ vioet 380 nm

4 Physics of Light Some exampes of the refectance spectra of surfaces % Photons Refected Red Yeow Bue Purpe Waveength nm dominant waveength or dominant frequency

5 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

6 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

7 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

8 Intensity & Brightness intensity Spectrum nm 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

9 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

10 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

11 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

12 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

13 Coor Matching Experiment 1

14 Coor Matching Experiment 1 R: nm G: nm B: nm R G B

15 Coor Matching Experiment 1 R: nm G: nm B: nm R G B

16 Coor Matching Experiment 1 The primary coor amounts needed for a match R G B

17 Coor Matching Experiment 2

18 Coor Matching Experiment 2 R: nm G: nm B: nm R G B

19 Coor Matching Experiment 2 R: nm G: nm B: nm R G B

20 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

21 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

22 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

23 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 = r g b y = r g b z = r g b

24 CIEXYZ Coor Space

25 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

26 CIEXYZ Coor Space n CIE chromaticity diagram encompasses a the perceivabe coors in 2D space x,y

27 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= x = = = y = = = e.g.2 X=20, Y=40, Z= x = = = y = = =

28 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

29 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!

30 CIE Chromacity Diagram n Compementary coors : together produce white coor. n Iuminant C average dayight

31 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

32 RGB Coor Mode Red, Green, Bue ights: additive mode Used in video monitor dispays C = R, G, B = RR + GG + BB Gray scae

33 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 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

34 CMYK Exampe

35 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

36 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 =382,720 coors

37 HSL Coor Mode u u Hue H, saturation S, ightness L, Hue & Saturation give a chromatic information Hue: [0,360] Saturation, Intensity : [0,1]