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Digital Image ProcessingChapter 5:

Color Image Processing

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(Images from Rafael C. Gonzalez and Richard E.

Wood, Digital Image Processing, 2ndEdition.

Spectrum of White LightSpectrum of White Light

1666 ir Isaac !e"ton, 2# $ear old, disco%ered "hite light s&ectr'm.

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Electromagnetic SpectrumElectromagnetic Spectrum

isi)le light "a%elength* from aro'nd #++ to ++ nm

1. -or an achromatic (monochrome light so'rce,

there is onl$ 1 attri)'te to descri)e the /'alit$*intensit$

2. -or a chromatic light so'rce, there are 0 attri)'tes to descri)ethe /'alit$*

Radiance total amo'nt of energ$ flo" from a light so'rce (Watts

'minance amo'nt of energ$ recei%ed )$ an o)ser%er (l'mens

3rightness intensit$

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Sensitivity of Cones in the Human EyeSensitivity of Cones in the Human Eye

64 millions cones

in a h'man e$e 4 65 sensiti%e to Red light

4 00 sensiti%e to Green light

4 2 sensiti%e to 3l'e light

Primar$ colors*

Defined CIE in 1701

Red ++ nm

Green 5#6.1nm

3l'e #05.8 nm

CIE Commission Internationale de l9Eclairage

(:he International Commission on Ill'mination

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Primary and Secondary ColorsPrimary and Secondary Colors

Primar$color

Primar$

color

Primar$

color

econdar$

colors

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Primary and Secondary Colors (cont.)Primary and Secondary Colors (cont.)

;dditi%e &rimar$ colors* RG3

'se in the case of light so'rces

s'ch as color monitors

')tracti%e &rimar$ colors* C

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R! Color "odelR! Color "odel

P'r&ose of color models* to facilitate the s&ecification of colors in

some standard

RG3 color models*4)ased on Cartesian

coordinate s$stem.

:he n'm)er of )its 'sed

to re&resent each &i?el in

RG3 &ace is called the

&i?el De&th.

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R! Color Cu#eR! Color Cu#e

R 8 )its

G 8 )its3 8 )its

Color de&th 2# )its

16216 colors

@idden faces

of the c')e

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R! Color "odel (cont.)R! Color "odel (cont.)

Red fi?ed at 12

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C"$ and C"$% Color "odelsC"$ and C"$% Color "odels

=

B

G

R

Y

M

C

1

1

1

C C$an

<

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HS& Color "odelHS& Color "odel

RG3, C

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@'e* dominant color corres&onding to a dominant

"a%elength of mi?t're light "a%e.(dominant color as

&ercei%ed )$ an o)ser%er.

at'ration* Relati%e &'rit$ or amo'nt of "hite light mi?ed

"ith a h'e (in%ersel$ &ro&ortional to amo'nt of "hite

light added

3rightness* Intensit$

Color Characteri'ationColor Characteri'ation

@'e

at'rationChromaticit$

amo'nt of red (B, green (= and )l'e ( to form an$ &artic'lar

color is called tristimulus.

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Hue and Saturation on Color PlanesHue and Saturation on Color Planes

1. ; dot is the &lane is an ar)itrar$ color

2. @'e is an angle from a red a?is.

0. at'ration is a distance to the &oint.

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HS& Color "odel (cont.)HS& Color "odel (cont.)

Intensit$ is gi%en )$ a &osition on the %ertical a?is.

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HS& Color "odelHS& Color "odel

Intensit$ is gi%en )$ a &osition on the %ertical a?is.

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Eample HS& Components of R! Cu#eEample HS& Components of R! Cu#e

@'e at'ration Intensit$

RG3 C')e

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Converting Colors from R! to HS&Converting Colors from R! to HS&

>

=

GB

GBH

if06+

if

[ ]

[ ]

+

+=

212

1

(((

((2

1

cosBGBRGR

BRGR

BGRS

++=

01

.(01 BGRI ++=

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Converting Colors from HS& to R!Converting Colors from HS& to R!

.1( SIB =

+=

6+cos(cos1HHSIR

.(1 BRG +=

RG sector* 12++

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Eample HS& Components of R! ColorsEample HS& Components of R! Colors

@'e

at'ration Intensit$

RG3

Image

E l " i l i HS& C

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Eample "anipulating HS& ComponentsEample "anipulating HS& Components

@'e

at'ration Intensit$

RG3

Image @'e at'ration

Intensit$ RG3

Image

C l & P i

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Color &mage ProcessingColor &mage Processing

:here are 2 t$&es of color image &rocesses

1. Pse'docolor image &rocess* ;ssigning colors to gra$

%al'es )ased on a s&ecific criterion. Gra$ scale images to )e &rocessed

ma$ )e a single image or m'lti&le images s'ch as m'ltis&ectral images

2. -'ll color image &rocess* :he &rocess to mani&'late real

color images s'ch as color &hotogra&hs.

P d l & P iP d l & P i

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Pseudocolor &mage ProcessingPseudocolor &mage Processing

Wh$ "e need to assign colors to gra$ scale image

;ns"er* @'man can disting'ish different colors )etter than different

shades of gra$.

Pse'do color false color * In some case there is no Fcolor conce&t

for a gra$ scale image )'t "e can assign Ffalse colors to an image.

& t it Sli i * it Sli i& t it Sli i * it Sli i

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&ntensity Slicing or *ensity Slicing&ntensity Slicing or *ensity Slicing

>

=

TyxfC

TyxfCyxg

,(if

,(if,(

2

1

-orm'la*

C1 Color !o. 1

C2

Color !o. 2

:

Intensit$

Co

lor

C1

C2

:+ 41

; gra$ scale image %ie"ed as a 0D s'rface.

& t it Sli i E l& t it Sli i E l

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&ntensity Slicing Eample&ntensity Slicing Eample

;n B4ra$ image of a "eld "ith crac>s

;fter assigning a $ello" color to &i?els "ith

%al'e 255 and a )l'e color to all other &i?els.

" lti L l & t it Sli i" lti L l & t it Sli i

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"ulti Level &ntensity Slicing"ulti Level &ntensity Slicing

kkk lyxflCyxg

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"ulti Level &ntensity Slicing Eample"ulti Level &ntensity Slicing Eample

kkk lyxflCyxg er

:h$roid Phantom.

;fter densit$ slicing into 8 colors

L l t C l + f ti L l t C l + f ti

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ray Level to Color +ransformationray Level to Color +ransformation

;ssigning colors to gra$ le%els )ased on s&ecific ma&&ing f'nctions

Red com&onent

Green com&onent

3l'e com&onent

Gra$ scale image

L l t C l + f ti E lray Level to Color +ransformation Eample

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(Images from Rafael C.

Gonzalez and Richard

E. Wood, Digital ImageProcessing, 2ndEdition.

ray Level to Color +ransformation Eampleray Level to Color +ransformation Eample

;n B4ra$ image of a

garment )ag "ith a

sim'lated e?&losi%e

de%ice

;n B4ra$ image

of a garment )ag

Color

coded

images

:ransformations

L l t C l + f ti E lray Level to Color +ransformation Eample

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Gonzalez and Richard

E. Wood, Digital ImageProcessing, 2ndEdition.

ray Level to Color +ransformation Eampleray Level to Color +ransformation Eample

;n B4ra$ image of a

garment )ag "ith a

sim'lated e?&losi%e

de%ice

;n B4ra$ image

of a garment )ag

Color

codedimages

:ransformations

Pse docolor CodingPseudocolor Coding

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Pseudocolor CodingPseudocolor Coding

Hsed in the case "here there are man$ monochrome images s'ch as m'ltis&ectral

satellite images.

!asics of ,ull Color &mage Processing!asics of ,ull Color &mage Processing

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!asics of ,ull-Color &mage Processing!asics of ,ull-Color &mage Processing

2

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EampleEample ,ull-Color &mage and ariouis Color Space Components,ull-Color &mage and ariouis Color Space Components

Color image

C

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Color +ransformationColor +ransformation

-orm'lation*

[ ].,(.,( yxfTyxg =

f(x,y in&'t color image, g(x,y o't&'t color image

T o&eration on fo%er a s&atial neigh)orhood of (x,y

When onl$ data at one &i?el is 'sedin the transformation, "e

can e?&ress the transformation as*

.,,,( 21 nii rrrTs

= i 1, 2, , n

Where ri color com&onent of f(x,y

si color com&onent of g(x,y

Hse to transform colors to colors.

-or RG3 images, n 0

Eample Color +ransformationEample Color +ransformation

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Eample Color +ransformationEample Color +ransformation

.,(.,(

.,(.,(

.,(.,(

yxkryxs

yxkryxs

yxkryxs

BB

GG

RR

=

=

=

-orm'la for RG3*

.,(.,( yxkryxs II =

-orm'la for CJ1.

k +.

I H,S

Color ComplementsColor Complements

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Color ComplementsColor Complements

Color com&lement re&laces each color "ith its o&&osite color in the

color circle of the @'e com&onent. :his o&eration is analogo's to

image negati%e in a gra$ scale image.

Color circle

Color &mage SmoothingColor &mage Smoothing

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Color &mage SmoothingColor &mage Smoothing

/ "ethods1. Per4color4&lane method*for RG3, C

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Color &mage Smoothing Eample (cont.)Color &mage Smoothing Eample (cont.)

Color image Red

Green 3l'e

Color &mage Smoothing Eample (cont )Color &mage Smoothing Eample (cont )

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@'e at'ration Intensit$

Color image

@I Com&onents


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mooth all RG3 com&onents mooth onl$ I com&onent of @I

(faster


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Difference )et"een

smoothed res'lts from 2methods in the &re%io's

slide.



Color &mage SharpeningColor &mage Sharpening

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Color &mage SharpeningColor &mage Sharpening

We can do in the same manner as color image smoothing*

1. Per4color4&lane method for RG3,C

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Color &mage Sharpening Eample (cont.)Color &mage Sharpening Eample (cont.)

Difference )et"een

shar&ened res'lts from 2methods in the &re%io's

slide.

Color SegmentationColor Segmentation

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Color SegmentationColor Segmentation

/ "ethods

1. egmented in @I color s&ace*

; thresholding f'nction )ased on color information in @ and Com&onents. We rarel$ 'se I com&onent for color image

segmentation.

2. egmentation in RG3 %ector s&ace*; thresholding f'nction )ased on distance in a color %ector s&ace.

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egmentation in @I model*

K Color is con%enientl$ re&resented in the h'e

image.

K at'ration is 'sed as a mas>ing image inorder to isolate f'rther regions of interest in

the h'e image.

K Intensit$ image is 'sed less fre/'entl$ forsegmentation of color images. 3eca'se it

carries no color information.

Color Segmentation in HS& Color SpaceColor Segmentation in HS& Color Space

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Color Segmentation in HS& Color SpaceColor Segmentation in HS& Color Space

@'e

at'ration Intensit$

Color image

1 2

0 #


Gonzalez and Richard E.Wood, Digital Image

Processing, 2ndEdition.

Color Segmentation in HS& Color Space (cont.)Color Segmentation in HS& Color Space (cont.)

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Prod'ct of and

5 6

8

523inar$ thresholding of com&onent

"ith : 1+

@istogram of 6 egmentation of red color &i?els

Red &i?els


Gonzalez and Richard E.

Wood, Digital Image



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Color image egmented res'lts of red &i?els


Gonzalez and Richard E.

Wood, Digital Image


Color Segmentation in R! ector SpaceColor Segmentation in R! ector Space

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Color Segmentation in R! ector SpaceColor Segmentation in R! ector Space

1. Each &oint "ith (R,G,3 coordinate in the %ector s&ace re&resents

one color.

2. egmentation is )ased on distance thresholding in a %ector s&ace

>=TyxD

TyxDyxg

T

T

,,((if+

,,((if1,(

cc

cc

cT color to )e segmented.

c(x,y RG3 %ector at &i?el (?,$.D(u,v distance f'nction

Eample Segmentation in R! ector SpaceEample Segmentation in R! ector Space

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Eample Segmentation in R! ector SpaceEample Segmentation in R! ector Space

Color image

Res'lts of segmentation in

RG3 %ector s&ace "ith :hreshold%al'e

Reference color cTto )e segmented)o?thein&i?elofcolora%erage=

Tc

T 1.25 times the D of R,G,3 %al'es

In the )o?

radient of a Color &mageradient of a Color &mage

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radient of a Color &mageg

ince gradient is define onl$ for a scalar image, there is no conce&t

of gradient for a color image. We can9t com&'te gradient of each

color com&onent and com)ine the res'lts to get the gradient of a colorimage.

Red Green 3l'e

Edges

We see

# o)Lects.

We see

2 o)Lects.

radient of a Color &mage (cont.)radient of a Color &mage (cont.)

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radient of a Color &mage (cont.)g ( )

Mne "a$ to com&'te the ma?im'm rate of change of a color image

"hich is close to the meaning of gradient is to 'se the follo"ing

form'la* Gradient com&'ted in RG3 color s&ace*

[ ]2

1

2sin22cos((2

1(

+++= xyyyxxyyxx gggggF

( )

=

yyxx

xy

gg

g2tan

2

1 1

222

x

B

x

G

x

R

gxx

+

+

=

222

y

B

y

G

y

R

gyy

+

+

=

y

B

x

B

y

G

x

G

y

R

x

Rgxy

+

+

=

radient of a Color &mage Eampleradient of a Color &mage Eample

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M)tained 'sing

the form'lain the &re%io's

slide

'm of

gradients of

each colorcom&onent

Mriginal

image

Difference

)et"een2 and 0

2

0

2 0

g pg p

radient of a Color &mage Eampleradient of a Color &mage Eample

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Gradients of each color com&onent

Red Green 3l'e

g pg p

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