ch t chapter 6 color image processing - bgudip111/wiki.files/dip3e_chapter06_art.pdf · digital...

Digital Image Processing, 3rd ed.Digital Image Processing, 3rd ed.

www.ImageProcessingPlace.com

Gonzalez & Woods

Ch t 6Ch t 6Chapter 6Color Image Processing

Chapter 6Color Image Processing

1018Ult i l t

10121014101610

Infrared

UltravioletVisible

106108101010

AM R diFM Radio + TVMicrowave

102104106 AM Radio

Gonzalez & Woods

ColorimetricColorimetricColor Perception involve Hue, Saturation, and Lightness Hue :distinguish among colors such as red, green, and purple.g g , g , p pSaturation :refer to how color far from gray.Lightness: the perceived intensity of a reflecting object.Brightness :refer to the perceived intensity of self luminousBrightness :refer to the perceived intensity of self-luminous.

White “Pure”color

Artists TermsTint: results of adding white pigments

GraysShades

Tonesg p g

pure pigmentsShade: comes from adding black pigments

to pure pigments

BlackTone:results of adding both black and white

pigments to pure pigments

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Color Models: GreenColor Models: The Newton Color Circle

CyanYellow

BlueRed

• The Newton color circle provides a convenient way to perceive

Magenta

p y pthe additive mixing properties of colors.

• The R,G,B and their complementary colors C,M,Y are placed on the circle in the order of the wavelengths of the corresponding

the circle in the order of the wavelengths of the corresponding spectral colors.

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• The separation of colors by a prism expose a continuous range of spectral colors

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• A spectral color is composed of a single wavelength p p g g• The helium-neon laser monochromatic light is red (632 nm). • Most colored objects give off a range of wavelengths and the

characterization of color is much more than the statement ofcharacterization of color is much more than the statement of wavelength.

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Primary and Secondary colorsPrimary and Secondary colors

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St d d C l M d lStandard Color ModelCommission Intenationale de l’Eclairage (CIE), 1931 defined three standard

i i ll d X YZ t l R d G Blprimaries, called X,Y,Z to replace Red, Green, Blue.

The primaries are used to match color by using three corresponding by us g t ee co espo d gcolor-matching functions

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CIE Chromatic DiagramgChromatic values depend on dominant wavelength and saturation and independentof luminous energy.of luminous energy.Consider a color C, the we can Write C = XX + YY + ZZNormalize Against X+Y+Zgx = X/(X+Y+Z) y = Y/(X+Y+Z) z = Z/(X+Y+Z) We know that x+y+z = 1, and the luminanceinformation usually in Y (Y cef.), thus we can recover X,Y,Z X Y ( / ) Y Y Z Y(1 )/

The XYZ space

X = Y (x/y) ; Y = Y ; Z = Y(1-x-y)/y Plotting these parameters

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Ch t 6Ch t 6XYZ Color Space

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When two color A and B are addedW e wo co o a d a e addedtogether new color C lies on the lineconnects both colors.In the side Figure, B defines the dominantwavelength, and the ratio AC to BC expressedas a percent of the excitation purity of A.The closer A to C the more light A includes.

Complementary colors are those that can bemixed to produce white light. D and E on the side Figure are complementary colorsside Figure are complementary colors.Nonspectral color are those that can not be defined by dominant wavelength such as F.Color gamuts or color ranges is the effect of

Color gamuts or color ranges is the effect of adding colors together

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RGB Color ModelThe color range (gamut) RGB model is defined by the CRT’s phosphor.

C = RR + GG + BB

Let us look at these colors in XYZ spaceLet us look at these colors in XYZ spaceRGB NTSC CIE MonitorR (0.67, 0.33) (0.73, 0.26) (0.62, 0.34)G (0.21, 0.71) (0.27, 0.71) (0 26 0 59)G (0.21, 0.71) (0.27, 0.71) (0.26, 0.59)B (0.14, 0.08) (0.16, 0.01) (0.15, 0.07)

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Ch t 6Ch t 6CMY Color Model

Cyan magenta and blue are the complements of red green blueCyan, magenta, and blue are the complements of red, green, blue. CMY is important when dealing with hardcopy that deposit color pigments onto paper.

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YIQ Color Model

YIQ is used by the US commercial TV.

Q• YIQ model exploits two properties of the visual system

– More sensitive to changes luminance than to change hue or saturationObj t th t t l ll t f fi ld f i d– Object that cover an extremely small part of our field of view, produce a limit color sensation.

• Y is the luminance (the same Y in XYZ space).h h i i i d d d d i d• The chromaticity is encoded encoded in I and Q

• Only Y component will show black/White TV• More bits are used for Y, and either I or Q has less bits than the other.

321027505960114.0587.0299.0

311.0528.0212.0321.0275.0596.0

Gonzalez & Woods

HSI ModelHSI Model The relationship betweenRGB and HSI

RGB to HSIGB

]))(()[(2)()(cos

BGBRGRBRGR

)],,[min()(

]))(()[(2

BGRBGR

BGBRGR

3/)( BGRI

Gonzalez & Woods

Hue and saturation in the HSI color model.• The angle from the red axis• The angle from the red axis

gives the hue• The length of the vector

i h iis the saturation.

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HSI RGBHSI to RGB

)1()1200(

SIBHfor

)()60cos(

)cos(1

)(3 BRIG

240360240120240120

HHHHHH

)cos(1

)1(240360240

SIBHHH

)(3)60cos(

Gonzalez & Woods

In various color processing applications it is possible to use the corresponding Red, p g ,Green, and Blue channels

Gonzalez & Woods

l di fColor Coding for visualization

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Color Image ProcessingColor Image Processing

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Color Transformation

Gonzalez & Woods

ch t chapter 6 color image processing - bgudip111/wiki.files/dip3e_chapter06_art.pdf · digital...

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