Color Vision: Understanding Colors, Color Spaces, and Color Effects, Slides of Computer Science

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Color

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Review of last week

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CIE-Lab (a.k.a. CIE Lab*)^ Image adapted from Wyszecki, G., a

nd W. S.^ Stiles, Color science: Concepts and methods, quantitative data and formulae.

Wiley-Interscience;

2nd Edition. July 2000. ISBN: 0471399183

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Perceptually Uniform Space: MacAdam • In color space CIE-XYZ, the perceiveddistance between colors is not equaleverywhere • In perceptually uniform color space,Euclidean distances reflect perceiveddifferences between colors • MacAdam ellipses (areas ofunperceivable differences) becomecircles

550540560 (^530520) 510 490 480 470

(^450460) .

y x .20.10. .65.60.55.50.45 .25.25.

.15.

. Spectrum locus.35^ .40^.

.60^ .55. .65.

.30 400 nm

610620650 700 nm 590600 570580 Purple line

Wyszecki, G. and W. S. Stiles.

Color science: Concepts and Methods, Quantitative Data and Formulae.

Wiley-Interscience, 2nd ed. July 2000. ISBN: 0471399183. Image adapted from:

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Color Vision

Hue Saturation Value^ •^

One interpretation in spectrum space • Not the only one because of metamerism • Dominant wavelength(hue) • Intensity • Purity (saturation)

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Color Vision

CIE color space • Match

color

at^ some point

A

•^ A

is^ mix

of^ white C,^ spectral

B!

-^ What

is^ dominant wavelength

of^ A

-^ What

is^ excitation purity

of^ A

• Move along AC/BC

C

(^520540510500490480) 0.1^400 0.10.

B^560 A D

E C F G

580 600

700

0.^

x

y 0.8 0. Hunt, R. W. G.

The Reproduction of Colour.

John Wiley & Sons Incorporated. September

Image adapted from:2004. ISBN: 0-470-02425-9.

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Color terms (Fairchild 1998 • Color • Hue • Brightness vs. lightness • Colorfulness and Chroma • Saturation • Unrelated and related colors

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Color^ – chromatic and achromatic content. This attribute can

be described by chromatic color names such asyellow, orange, brown, red, pink, green, blue, purple,etc., or by achromatic color names such as white,gray, black, etc., and qualified by bright, dim, light,dark, etc., or by combinations of such names. – Note: Perceived color depends on the spectraldistribution of the color stimulus, on the size, shape,structure, and surround of the stimulus area, on thestate of adaptation of the observer's visual system, andon the observer's experience of the prevailing andsimilar situations of observations.

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Hue • Hue^ – Attribute of a visual sensation according to which an

area appears be similar to one of the perceived colors:red, yellow, green, and blue, or to a combination oftwo of them.

• Achromatic Color^ – Perceived color devoid of hue. • Chromatic Color^ – Perceived color possessing a hue.

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Brightness vs. Lightness • Brightness^ – Attribute of a visual sensation according to which an

area appears to emit more or less light.

• Lightness:^ – The brightness of an area judged relative to the

brightness of a similarly illuminated area that appearsto be white or highly transmitting.

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Saturation^ – Colorfulness of an area judged in proportion to its

brightness.

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Plan • Color Vision • Color spaces • Color effects^ – Definitions^ – Spatial sensitivity^ – Color illusion and color appearance • Producing color

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Contrast processing •^ Receptors are wired toother neurons •^ Center-surroundorganization •^ Sensitive mostly to localcontrast

+^

• • (^) +
• • • • +++

• • • +++++

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-^ - --

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Land Retinex and local contrast

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