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color

rein van den boomgaard

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color images

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color images

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color images

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the physics of color

Light is electromagnetic energy

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spectral color vs object color

Lamp

objectcolor

beamcolor

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light source

sensor

object

object color

l(λ)

c (λ)

l(λ)c (λ)

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object color

e(λ )=m l(λ) c (λ) variation due to geometry

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photoreceptors in the retina

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photoreceptors in the retina

In the retina photoreceptors measure the light

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photoreceptors in the retina

Rodsfor low light levels (only B/W)

Conesfor normal light levels

for color detectionThree types of cones sensitive to different wavelenghts

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sensitivity of the cones

300 400 500 600 700 800 9000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

L

M

S

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example

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'calculate' SML

S=∫e (λ )s s(λ)d λ

M=∫e (λ)sm(λ)d λ

L=∫e (λ)sl(λ)d λ

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color blindness (see Wikipedia)

Protanopia: Lacking the long-wavelength sensitive retinal cones, those with this condition are unable to distinguish between colors in the green-yellow-red section of the spectrum. They have a neutral point at a wavelength of 492 nmthat is, they cannot discriminate light of this wavelength from white.

Deuteranopia: Lacking the medium-wavelength cones, those affected are again unable to distinguish between colors in the green-yellow-red section of the spectrum. Their neutral point is at a slightly longer wavelength, 498 nm.

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color blindness

about 10 percent of males is colorblindit is wise to check your colors in design to see whether

colorblind people can distinguish the important colors

http://colorfilter.wickline.org/

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colorimetrie

De SML gevoeligheidscurves zijn pas enige tientallen jaren met enige nauwkeurigheid bekend.

Kleursystemen zijn veel ouder

Colormatching: gebruik menselijk oog als meetinstrument

om zoveel mogelijk de subjectiviteit van de menselijke beoordeling uit te sluiten 'vragen' we de mens alleen over gelijkheid van kleuren te oordelen

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a 1 1pa 2 2pa 3 3p

t

color matching experiment

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rgb color matching functions

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xyz color matching matrix

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XYZ color system

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chromaticity coordinates

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xy – chromaticity diagram

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color reproduction

Faithfull color reproduction is possible using any three colorimetric independent light sources.

a1

a2

a3

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color reproduction

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color reproduction

a1a2 a3

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color gamut

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color gamut

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different color gamuts

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RGB cube

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RGB to XYZ

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the RGB color cube

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the RGB color cube

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the RGB color cube

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color camera’s

a color CCD camera is either:3 ‘parallel’ camera’s, one for Red, one for Green and one

for Blue, or

3 ‘interwoven’ camera’s (Red, Green and Blue pixels mixed on the CCD: this is a lot like the human retina)

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3 CCD color camera

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Bayer color mosaic

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finding Waldo

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punctal COLOR observations

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skin color

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skin pixels, not-skin pixelsRGB - space versus rgb - space

skin color

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skin color

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hue – saturation – value

hue: the dominant color (red/green/blue/...)

saturation: pure color (saturation = 1) or almost colorless (mixed with grey: saturation = 0)

value: the intensity (what you would see with a black and white camera)

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hue – saturation – value

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hue – saturation – value

BB

GG

RR

HH SS

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hue

BB

GG

RR

HH SS

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color (hue) histogram