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Grafisk Teknik

Reiner Lenz

Grafisk Teknik

Reiner Lenz

Grafisk Teknik

Reiner Lenz

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Content and Goals• Basic color perception and color vision facts• Mathematical modeling of color science/color image processing problems• Basic understanding of CIE colorimetry• Color Management Systems

BEFORE:Matlab, Linear Algebra

GRAFISK TEKNIK, TNM011

AFTER:TMN012, More Matlab, More Linear Algebra, … TNM025: Image Database Search

Part 0: Literature

Sharma: Digital Color Imaging Handbook

Sharma: Available at bibl.liu.se

http://www.engnetbase.com/books/1039/01.pdf

Selected pages from Chapter 1

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Westland, Ripamonti: Computational Colour Science

using Matlab

Available as e-book: under bibl.liu.se + netlibrary

http://www.netlibrary.com/AccessProduct.aspx?ProductId=108197

G.Wyszecki, W.S. Stiles: Color Science

The ”Color Bible”

M.D. Fairchild: Color Appearance Models

Describes how we perceive color. Additional text.

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S. Zeki: Inner Vision

Art/Brain/Color/Perception. Additional text.

Additional (older) Literature

• E.J. Giorgianni and T.E. Madden: Digital Color Management Addison-Wesley, 1998.

• P.K. Kaiser and R.M. Boynton: Human Color Vision, OSA, 1996.• L.W. MacDonald:Using color effectively in computer graphics. IEEE

Computer Graphics and Applications July/August 1999.• M.A. Webster:Human colour perception and its adaptation. Network, 1996.• J. Hardeberg: Acquisition and Reproduction of Color Images: Colorimetric andMultispectral Approaches, 2001 ($10 www.dissertation.com)

Part 1: Color Everywhere

• Color is important• Color is difficult• Color is useful

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Everybody knows what color isSearch for color on the web:a visual attribute of things that results from the light they emit or transmit or reflect; "a white color is made up of many different wavelengths of

interest and variety and intensity; "the Puritan Period was lacking in color"the timbre of a musical sound; "the recording fails to capture the true color of the original music"a race with skin pigmentation different from the white race (especially Blacks)an outward or token appearance or form that is deliberately misleading; "he hoped his claims would have a semblance of authenticity"; "he tried toany material used for its color; "she used a different color for the trim"(physics) the characteristic of quarks that determines their role in the strong interaction; each flavor of quarks comes in three colorsthe appearance of objects (or light sources) described in terms of a person's perception of their hue and lightness (or brightness) and saturationadd color to; "The child colored the drawings"; "Fall colored the trees"; "colorize black and white film"affect as in thought or feeling; "My personal feelings color my judgment in this case"; "The sadness tinged his life"modify or bias; "His political ideas color his lectures"decorate with colors; "color the walls with paint in warm tones"gloss or excuse; "color a lie"change color, often in an undesired manner; "The shirts discolored"having or capable of producing colors; "color film"; "he rented a color television"; "marvelous color illustrations"A property of quarks that expresses their behavior in the presence of the strong nuclear force; analogous to electrical charge, but there are threbroad band intensity of the spectrum through filters; if an object is equally bright as seen through different filters, the asteroid is referred t

between the brightness through two filters LEDs are designed to give off a specific color emission. The dominant wavelength is a quantitative measure of an LED color as perceived by the hum

range required for your application. Some applications may have color constraints in order to meet specific government specifications or regulatory guFor human beings: our perception of radiant visible energy seen as hue, intensity, value and temperature reflected from a surface, or transmitted

The measurement of white paper based on the color scale (L, a, b). "L" represents the lightness on a scale of 0 for black and 100 for perfect white, "1) Used to refer to perceived qualities that result from the response of vision to the wavelength of reflected or transmitted light. 2) Describes Light waves that reach the viewer's eye by transmission (through an object between the viewer and the light source) or by reflection (when light w

apple looks red because it absorbs all colors in white light except red, which it reflects. White objects reflect all and black objects absorb all ligconsists of the characteristics of light other than spatial and temporal inhomogeneities; light being that aspect of radiant energy of which a humColor in water can be caused by the presence of such things as plankton, decaying organic matter, industrial wastes, and sewage. "True color" - th

usually measured by comparing the color of a water sample to that of a fixed standard. Color is expressed in terms of "color units" where one color un(1) a visual sensation produced in the brain when the eye views various wavelengths of light; (2) the appearance of objects or light sources descr

sources.The phenomenon of color results from the interaction between a light source, an object and an observer. Standard mathematical models can be used t

data, and observers are quantified by the observer functions. These three elements can then be combined to calculate values that correspond to how theMeasured in color units that relate to a standard. A yellow-brown natural color is associated with lakes or rivers receiving wetland drainage. The

and therefore the depth at which plants can grow.Refers not to the actual color of things, but to the fact that there are two distinct kinds of each, and these are given the names `black', and `wThe particular color of a tape' when looking at the backing' regardless of the color of the adhesive.What a precision shooter hollers if the dealers give them any heat over setting the dice. In doing so, he announces his intention to leave the tab

denominations prior to his departure. The shooter will remain at the table to await the outcome of any contract wagers (non removable). If the shooterThe color scale is used to describe the color tones of a gemstone. For diamonds, the color scale ranges from D, meaning completely colorless, to Z

the color is measured by tone and hue. See also Tone and Hue.Response of the eye to different wavelengths of light. Ultraviolet < 400 nm, violet 400-424 nm, blue 424-491 nm, green 491-575 nm, yellow 575-585

Some History of Color Science

•Greece (400BC) :Four basic elements: earth, air, fire and waterInner fire sends out rays, they interact with outer rays emerging from the objects. Tiny copies of the objects are transferred back and compared in the mind

•Arab culture (Abu Ali Mohammed Ibn Al Hazen (965-1039 A.D.):Assumed that:human eye is similar to a pinhole cameracolor of an object depends on the color of the light and the properties of the object

•Leonardo da Vinci (1452-1519) :Perspective drawing and similarity to the pinhole camera

•Kepler (1571-1630) :Effects of lenses

•Newton (1643-1727) :Experiments with prismsWhite is a combination of colored lightsColor of an object is related to the ability to reflect the colored rays

•Trichromacy:J. C. Le Blon described how to print with the help of three colors in 1723M. Lomonosov described mixture of three primary colors and trichromatic perception in

1757Thomas Young described trichromacy in its modern form in 1802Helmholtz (1821-1894) popularizes trichromacy

Some Color Science History

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•Newton vs. Goethe:

Newton showed that white light can be understood as a combination of light of different wavelengths

Goethe claimed that complex processes can only be understood holistically

•Helmholtz vs. Hering:

Helmholtz showed that trichromacy is the basis of color perception since the human visual system is based on three sensors

Hering used psychological experiments that showed that

black/white red/green yellow/blue

are opposed to each other. So he postulated that the visual system is based on three opponent color

channels.

Objective vs. Subjective Color Theories

• Medicin (eye, brain, …)• Biology (animal vision)• Art• Technology• Mathematics• Physics• Psychology• Economy• …

Color is multi-disciplinary

Color Matters - Some Observations• Printing:

Was an art requiring long experience. This knowledge is rapidly disappearing.Printing today is to a large extend a digital techniqueComputational techniques are required

• Networking: Databases/Printing/Content/Construction• Digital Cameras replace analogue cameras • Computational photography: Camera+computer=1 System • Computer Graphics and Visualization:

Realistic color is important

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New Technologies• Everybody can create and print documents

• Digital Cameras/Ink Jet Printers/Monitors

• Multimedia Computers

• Digital Cinema/Camera Telephone

• Computational photography

• …

All of them need tools to describe and process color information

Graphics/Movies/Cosmetics/Medicin

Realistic Skin Modelling (Tsumura, Chiba U, Japan)

Networking

CadDesignProductionMarketingSales

GermanyItalyChinaSwedenEverywhere

Correct PropertiesInteraction with surroundingsQuality controlReproduction on monitorReproduction in catalogueReproduction in newspaperPrint Quality Control on different paper…

Exact description and communication of color is essential

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Photography

• Analog Digital• Chemical Signal

01001010110010010010101100100100101011001001001010110010

0100101011011010010010101101101001001010110110100100101011011010

0100101011011010010010101101101001001010110110100100101011011010

010010101101101010001111010011010100101011011010100011110100110101001010110110101110100101011011010111

0100101011001001010110

Canon Digital Camera Software

Color is important in Search EnginesScene=objects+illuminations

Image retrieval

Signal processingImage understanding

Digital cameraAnalog camera

Example: http://www.matton.se

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Digital Cameras – What’s next?

Computer Aug. 2006

Computational Photography-The Next Big StepComputational Cameras: Redefining the ImageLight Fields and Computational ImagingThe Moment CameraVirtual Cinematography: Relighting through Computation

Multispectral SystemsAixperts-Aachen GermanyMultispectral Scanner and Display for Industrial Applications

Sony Camera withinternal 4 channelsensor

Crisatel Scannerof paintings

Chiba University Japanthree-dimensional, five-channel camera

Part 2: Human Color Vision

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COLOR IS INSIDE THE BRAIN!COLOR IS INSIDE THE BRAIN!Some illustrations that color is more than physics

Physics-Psychophysics

Simultaneous Contrast

Color needs contours

Hans Irtel

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Simultaneous Contrast

Hans Irtel

Color Spectra

•Color originates in light

•Light is electromagnetic radiation

•It can be described by wavelength

•Humans can see light of wavelengths

in the range 380nm to 800nm

Electromagnetic Radiation

Wikipedia

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Functions of wavelength

SpectrumS(λ) = Number of photons of wavelength λ

The Human Eye - Hardware

Human eye

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Two type of sensors:

• Rods responsible for low-intensity situations

(only intensity, black-white, detection)

• Cones active in normal light conditions

(three types enabling to trichromatic-color vision)

Human Eye: Receptors

The retina

Flow of Light

Psychophysics:Weber FechnerLaw

Given an intensity I and perceived brightness R ∆R is the smallest increment such difference between R and R+∆R can be seenThen

leads to

or differential equation

which means that R must be an exponential function R(I) = c1exp(c2I)

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Human color vision

Spectral sensitivity curves are Probability Curves:

•Photon of a given wavelength hits cone ->

an impulse is generated with a given probability

•After the impulse is generate it is not possible

to recover the wavelength of the photon

Human color vision is most sensitive to

medium range wavelength around 555nm

Known as V(λ)

Relative sensitivity of the eye

Human cones are sensitive for

short (S-cones)

medium (M-cones) and

long (L-cones) wavelengths

Number of L-M-S cones = 40:20:1

No S-cones in the centre of the

retina!

Characteristics of human color vision

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Spectral sensitivity of human pigments

Human/Animal Color Vision

• Most animal vision is intensity based (no color)

• First a second type of cones were added, the S-conesThis is the ancient system

• Then (30 million years ago) middle range cones modifyinto M- and L-conesThis is the modern system

Color Blindness

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Color Blindness• roughly 1 in 10 men are fully or partly colour blind.

• one of the three types of colour detectors is either faulty or missing

Strawberries. Strawberries as they would appear

to someone who is red/green colorblind.

http://www.vischeck.com/info/wade.php

Types of color blindness•Protanope: 1% male, 0.02% female

400-492nm, blue 492-700nm yellow

L pigment missing

•Deuteranopia: 1% male, 0.01% female

400-498nm blue 498-700nm yellow

M pigment missing

•Tritanopia: 0.002% male, 0.001 female

400-570nm blue, 570-700nm red

Probably S pigment missing

Types of color blindness II

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Example 1

http://www.vischeck.com/examples/

Example 2

http://www.vischeck.com/examples/

Illustration of color deficiencyInteractive demonstration of colour appearance for the 'colour-b

http://www.tsi.enst.fr/~brettel/DaltonDemo/DD08.html

Vischeck simulates colorblind vision

http://www.vischeck.com

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Further comments

•Differentiation between M- and L-cones may result from discrimination for certain fruits

•There may be more than 3 color receptors

Young-Maxwell-Helmholtz/Hering

Young-Maxwell-Helmholtz described color vision in terms of three channels, based on the three receptor types red-green-blue (trichromatic model)

Hering developed oppenent color pairs:red-green, blue-yellow, black-white

There is no greenish-red but reddish-yellow (opponent color model)

Trichromatic and opponent color models are combined in newer models of color vision