Prof. Muhammad Saeed

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WavelengthNote that the rainbow does not contain any magenta. It is nonspectral.

Color Models:

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Newton’s Color Wheel Replaced Aristotle’s color model based on light and darkness.

Color Models:

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Color Models:

Spectrumultraviolet light

Wavelength (nm)700 600 500 400

• Seen in physics, physical phenomena (rainbows, prisms, etc)

• 1 Dimensional color space

Infrared light

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Sensitivity and Models

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Tristimulus Color Theory

• Any color can be matched by a mixture of three fixed base colors (primaries)

• Eye has three kinds of color receptors called cones

• Eye also has rods (low light receptors)

Color Receptors in Eye0.200 .180 .160 .140 .120 .100 .080 .060 .040 .020 .00

600560440 520 640400 680480Wavelength λ (nm)

Frac

tion

of li

ght a

bsor

bed

by e

ach

type

of c

one

Color Models:

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Wavelength is in nanometers

Color Models:

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Traditional, Artistic:• RGB• CMY• CMYK• HSV• HSL

Perceptually Based:• XYZ (Tristimulus)• Xyz• Hunter-Lab• CIE-L*ab• CIE-L*CH° • CIE-L*CH°• CIE-L*ab• CIE-L*uv

Color Models:

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Color Models:

Tints, Tones and Shades:

White Pure Color

Black

Shades

Tones

Grays

Tints

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Additive Primaries: (r,g,b)

(1,0,1)(1,0,1)

(0,0,1 )(0,0,1 )

magentamagenta

whitewhite(1,1,1)(1,1,1)

(0,1,0)(0,1,0)greengreen

(1,1,0)(1,1,0)yellowyellow

(0,1,1)(0,1,1)cyancyan

blueblue

(1,0,0)(1,0,0)redred

Color Models:

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Color Models:

(0,0,1 )(0,0,1 )blueblue

(1,0,1)(1,0,1)magentamagenta

(0,1,1)(0,1,1)cyancyan

(0,1,0)(0,1,0)

(1,1,0)(1,1,0)yellowyellow

(1,0,0)(1,0,0)redred

whitewhite(1,1,1)(1,1,1)

(0,0,0)(0,0,0)blackblack

graygray

RGB Model:

greengreen

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(0,0,1 )(0,0,1 )blueblue

(1,0,1)(1,0,1)magentamagenta

(0,1,1)(0,1,1)cyancyan

(0,1,0)(0,1,0)greengreen

(1,1,0)(1,1,0)yellowyellow(1,0,0)(1,0,0)

redred

(1,1,1)(1,1,1)whitewhite

Color Models:

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Looking at color cube along major diagonal

Color Models:

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(0,0,1)(0,0,1)

Color Models:

(1,1,0)(1,1,0)yellowyellow

(0,1,0)(0,1,0)greengreen

(0,1,1)(0,1,1)cyancyan

blueblue

(1,0,1)(1,0,1)magentamagenta

(1,0,0)(1,0,0)redred

blackblack(0,0,0)

Subtractive Primaries: (r,g,b)

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120˚

0˚

V

SH

1.0

0.0

240˚

yellowyellowgreengreen

cyancyan redred

magentamagentablueblue

• Introduced by Albet Munsell, late 1800s.

• He was an artist and scientist

• Hue: Color• Saturation/Chroma:

Strength of a color– Neutral gray has 0

saturation• Brightness/Value: • Intensity of

light emanating from image

Color Models:

H S V MODELH S V MODEL

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SaturationColor Models:

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James C. Maxwell’s Color Model

magentamagentablueblue

cyancyan

greengreen

redred

yellowyellow

unsaturated cyan unsaturated cyan

whitewhite

Color Models:

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1.0

S

L

0˚

0.0H

whitewhite

blackblack

redred

Color Models:

HLS Model (Hue, Lightness, Saturation)

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Color Models:

HSV to RGB

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Color Models:

RGB to HSV

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Color Models:

CIE* Color Space( X, Y, Z ) represents an imaginary basis that does not correspond to what we see

Define the normalized coordinates:x = X / ( X + Y + Z )y = Y / ( X + Y + Z )z = Z / ( X + Y + Z )

* Commission Internationale de l'Êclairage

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x + y + z = 1

x = X / ( X + Y + Z )y = Y / ( X + Y + Z )z = Z / ( X + Y + Z )

z

y

x

The projection of the plane of the triangle onto the (X,Y) plane forms the chromaticity diagram that follows.

Color Models:

CIE Color Space of Visible ColorsColors

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Color Gamuts: CIE Color Charty

x

1.00 .90 .80 .70 .60 .50 .40 .30 .20 .1

1.0 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1.0

cyancyan

magentamagentaredredblueblue

green green

yellowyellow

400

490

500

510

520

600

700

580

560

540

whitewhite

Color Models:

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ideal redideal redideal blueideal blue

ideal greenideal green

redredblueblue

green green

cyancyanyellowyellow

whitewhite

400 nm

490 nm

500 nm

510 nm540 nm

560 nm

580 nm

700 nm

600 nm

520 nm

Color Gamuts: CIE Color Chart

Color Models:

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400

490

500

510520

600

700

580

560

540

Color Gamuts: CIE Color ChartColor Models:

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400

490

500

510520

600

700

580

560

540

R

B

G

The Color Gamuts of different displays and printers are not likely to match. Printers usually have smaller gamuts.

Color Gamuts: CIE Color ChartColor Models:

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Color Models:

CIE Chromaticity Diagram:

ZYXXx

ZYXYy

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400

490

500

510520

600

700

580

560

540

C2

C3

C1

The additive colors C1and C2 combine to form C3 on the line connecting C1 and C2.

Color Gamuts: CIE Color ChartColor Models:

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Color monitors are based on adding three the outputof three different light emitting phosphors.The nominal position of these on the CIE diagram isgiven by: x y zRed 0.628 0.346 0.026Green 0.268 0.588 0.144Blue 0.150 0.07 0.780

Color Models:

Reproducible colors:

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Color Models:

The monitor RG B representation is related to the CIE colors by the equation:

RGB to CIE:

BGR

zyx78.0144.0026.007.0588.0346.015.0268.0628.0

Color (RGB) to Gray Transformation:Red *= 0.33,Green *= 0.56,Blue *= 0.11

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CIE Chromaticity Diagram

Color Models:CIE Model (Commission Internationale de I’ Eclairage):

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Color Models:

Gamma Correction:

1'

'

)(

)(

ii

im

RkR

RKR

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