seminar - 4th year PERCEPTION OF...

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University of Ljubljana Faculty of Mathematics and Physics Department of Physics seminar - 4th year PERCEPTION OF COLORS Author: Jernej Laloˇ s Mentor: prof. dr. Marko Zgonik Ljubljana, May 2011 Abstract Vision is the most developed human sensory system; and humans see in colors. First we take a look at light and its interaction with matter. Then we examine human vision system with eyes and seeing - perception of vision. Next we examine perception of color, color properties, color mixing, color systems, classification and color reproduction. Lastly we conclude on the subject with the role of colors in human perception of nature and the world.

Transcript of seminar - 4th year PERCEPTION OF...

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University of LjubljanaFaculty of Mathematics and Physics

Department of Physics

seminar - 4th year

PERCEPTION OF COLORS

Author: Jernej Lalos

Mentor: prof. dr. Marko Zgonik

Ljubljana, May 2011

Abstract

Vision is the most developed human sensory system; and humans see in colors. First we take alook at light and its interaction with matter. Then we examine human vision system with eyes andseeing - perception of vision. Next we examine perception of color, color properties, color mixing,color systems, classification and color reproduction. Lastly we conclude on the subject with therole of colors in human perception of nature and the world.

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Seminar Perception of Colors Jernej Lalos

Table of Contents

1. Introduction .............................................. 12. Light and Matter .............................................. 13. Vision .............................................. 23.1 Human Eye .............................................. 3

Path of Light .............................................. 3Photoreceptors .............................................. 4Visual Phototransduction .............................................. 5

3.2 Perception of Colors .............................................. 5In the Retina .............................................. 5In the Brain .............................................. 6

4. Colors .............................................. 74.1 Appearance of Colors .............................................. 7

Properties of Colors .............................................. 7Color Mixing .............................................. 8

4.2 CIE Color Space .............................................. 94.3 HSL Color Model .............................................. 114.4 Reproduction of Colors .............................................. 12

RGB Color Model .............................................. 12CMYK Color Model .............................................. 13

5. Conclusion .............................................. 136. Literature .............................................. 14

1. Introduction

Physics deals with nature: it examines properties of energy and matter. Since physics does notexist per se, but is a science imagined and created by humans in their mind, it requires media inform of sensors to convert natural properties of energy and matter to a form which is observableby human senses. But human senses itself are in essence just media for human mind to observeits body and the world around its body. It is therefore only logical to examine more closely thenatural sensors of humans, because without them no artificial sensor constructing and indeed nophysical science would even be possible.

One such natural sensor system is vision. In fact, it is the most developed human sensorysystem. It starts with the eyes which sense electromagnetic radiation in form of light. Eyesconvert light into electric signals which are sent to the brain, home of the human mind. Brain thenconverts those signals to colorful images of the outside world. Humans see in colors - colors arethe end output of human vision system. But what do they mean? And how do they work?

We must also keep in mind that due to the subjective nature of human vision and perceptionon general, the study of it is rather phenomenological!

2. Light and Matter

Light is a part of electromagnetic radiation, mostly the part that is visible.

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Earth gets a vast majority of its light from the Sun. Sun emits electromagnetic radiationsimilarly as a black body. Spectrum of blackbody radiation at a particular temperature is describedwith the Planck’s law:

I(λ) =2hc2

λ51

ehcλkT − 1

, (1)

where λ is wavelength of light, h is Planck constant, c is speed of light in vacuum, k is Boltzmanconstant, T is absolute temperature (of the Sun T = 5750K) and e is the base of natural logarithm.

We can see that at this temperature the spectrum has its peak right between the wavelengthsof λ = 390nm and λ = 740nm. And coincidently, precisely that wavelength interval of theelectromagnetic spectrum is where the human eye is sensitive to the light. In other words: Sun isthe most bright natural source of light on Earth, so most of the eyes have adapted to be sensitiveto the most intensive part of electromagnetic radiation in Sun’s spectrum.

Figure 1: Solar spectral radiation compared to spectral radiation of a black body [16].

In nature, many phenomena have an effect on wavelength of light - so much, that it is usefulfor living organisms to distinguish between light of different wavelengths. Most common thingsthat can influence the spectrum of light are described below:

Some of the light arriving at an object can be reflected off, some absorbed in and sometransmitted through, depending on the wavelength of light and material properties. For example,light of a given wavelength can be absorbed, so only the remaining wavelengths can be seen.Light can also be scattered, or diffracted, or dispersed, or can interfere, or can interferecoherently, again depending on its wavelength, and so can be seen differently from different pointsof view. Light of certain wavelengths can originate from objects as well – it can be emitted byparticles.

All of these complex phenomena contribute to the spectrum and intensity of each beam of lightthat can be seen at each point in time and space. More complex eye, the natural light sensor,can distinguish between different combinations of wavelengths of light in certain interval. Withthat information, the brain than perceives certain combinations of wavelength of light as particularcolor; and also the difference between two combinations as difference in two colors.

3. Vision

Vision is an act of perceiving light as useful information for the beholder. It requires aninstrument which converts light to some sort of signal, a mechanism which processes that signal in

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an efficient manner and derives some sensible information out of it. The biological instrument inliving creatures, that can see, is the eye and the corresponding signal processing unit is the brain.Since we are interested mainly in human vision and perception of colors, we are going to take alook at the human eye and the human brain.

3.1 Human Eye

Eye is a camera-like instrument that makes seeing possible. Humans have two complex roundeyes that can be rotated around its center in its socket. Each one is around 24mm in diameter andhas a field of view of about 170◦ in horizontal axis and about 100◦ in vertical axis. Both eyestogether have a field of view of about 200◦ in horizontal axis - thus providing a human with about140◦ of forward-looking binocular vision. Most of this field of view is peripheral and only a smallportion of it is focused.

Figure 2: Cross-section of the right human eye with its most important parts [18].

PATH OF LIGHT

From the optical point of view, the path of light through the eye is the most interesting. Lightenters the eye through the cornea. This is the first and most powerful lens of the optical systemof the eye and has a relatively high refractive index n = 1, 376 (compared to that of air n ≈ 1).Cornea is combined with white sclera. They are the outermost part of the eye, and together theyhold its shape. Light then passes through the anterior chamber, filled with aqueous humor, whichhas a slightly lower refractive index.

Next, light goes through the pupil which is itself just an aperture of the colorful iris. Themain function of this circular muscle is to control the size of the pupil so that more or less lightmay enter the inside of the eye.

Behind the iris is the biconvex crystalline lens. Its function is to focus the incoming lighton the retina which lies on the inside of the eye. For that purpose, it is built from several nestedshells and has a refractive index of around n = 1, 406 which tends to be lower at the edges. Mostimportantly, it can change shape with the help of ciliary muscles and accommodates, thus enablingfine tuning of focus.

Light passes further through vitreous humor. This medium fills the inside of the eye and isright between the lens and the retina. It has slightly lower refractive index n = 1, 336.

The part, which actually detects light, is the retina. It is a fine layer lining the inner surfaceof the eye, full of nerves and light-sensitive receptors. Retina itself is layered with several layers of

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neurons interconnected by synapses. Light-sensitive photoreceptor cells are mainly of two types:rods and cones. Interestingly, they both lie in the inner layer of the retina; so the light, to reachthem, must pass through all the other neuron layers and even blood vessels.

There are two special spots on the retina: One is fovea. The cones are highly concentratedhere. It is responsible for sharp central vision and lies in the center of the eye’s optical axis. Secondis the blind spot. It is a place where optic nerve connects with the eye, and has no rods or cones.It is off-centered towards the nose.

Figure 3: Schematic representation of the path of light through the eye and the cross-section ofthe retina (right) [17].

PHOTORECEPTORS

Rods are photoreceptors that function well in low-light conditions and are therefore used forscotopic vision (at luminance levels of 10−6cd/m2 to 10−2cd/m2). There are roughly 120 millionof them in a human eye. Rods are very sensitive and can be excited with a single photon. They aremonochromatic, cannot distinguish colors, with peak sensitivity at wavelength of light of aroundλ = 500nm. The main light-sensitive pigment in rods is rhodopsin.

Cones are photoreceptors that function well in well-lit conditions and are therefore used forphotopic vision (at luminance levels of 1cd/m2 to 106cd/m2). There are about 6 million of themin a human eye. Human cones come in three different versions, each with a light sensitivity peakat a different wavelength. So called L (long) cones have peak sensitivity at around λ = 560nm, M

Figure 4: Relative sensitivity spectra for rods and each of the three types of cones: S - blue,M - green, L - red [8].

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(medium) cones have it at around λ = 530nm and S (short) cones at around λ = 430nm. Preciselythose three kinds of cones enable human day-time trichromatic vision! The main light-sensitivepigment in rods is called photopsin.

If an eye is to be likened to the camera, the iris would be the diaphragm with the pupil as itsaperture, crystalline lens would be the lens of the camera and the retina would be its film or, inmore modern ones, the image sensor.

VISUAL PHOTOTRANSDUCTION

In rods and cones in the retina photons of light are converted into electrical signals by theprocess of visual phototransduction.

Both rods and cones are similarly built and have a similar transduction mechanism in whichthe cell membrane has an important role. There are two currents that flow through the membrane:One is an ongoing outward potassium current which flows through non-gated K+-selective channelsand hyperpolarizes the photoreceptor at around −70mV. The other is an inward sodium current(also called dark current) which flows through gated sodium Na+-channels and depolarizes the cellto around −40mV. Photoreceptors have a high density of Na+– K+ pumps which enables them tomaintain a steady intracellular concentration of Na+ and K+ ions.

In the dark, when photoreceptor is not excited both currents flow through the membrane andthe cell is depolarized at about −40mV. At this voltage the voltage-gated calcium Ca2+-channelsare open which causes a steady high concentration of Ca2+ ions in the photoreceptor cell. Thiscauses an electro-chemical chain of events which sends a non-excitation signal to the neurons andthe brain.

When there is light, when photons reach photoreceptor cell, they cause an isomerisation ofpigments (rhodopsin in rods or three types of photopsin in cones). This than triggers a chain ofchemical reactions which leads to the closure of sodium Na+-channels in the cell membrane. Whenthose channels are closed the ongoing potassium current hyperpolarizes the cells which than closesthe voltage-gated calcium Ca2+-channels. Low concentration of Ca2+ ions in the photoreceptorcell causes another electro-chemical chain of events which sends an excitation signal to the neuronsand the brain.

The brighter the light that reaches the eye, more photoreceptors are excited and quicker whichthan generates signals that are interpreted as bright in the brain.

3.2 Perception of Colors

Perceprion of colors starts in the retina where signals form. Those are than transmitted to thebrain which processes and interprets them.

IN THE RETINA

For color vision, lateral interactions on the retina are especially important. The color of aparticular area of the visual scene depends on the spectral distribution of the light coming fromthat area and also on the spectral distribution and quantity of light coming from other regions ofthe visual field. The lateral interactions make this possible.

The simplified model of retinal function is this:Initial trichromacy represented by L, M and S cones is changed within the retina to a different

trichromatic code.The outputs of all cones are summed to provide a black-white luminance signal, which is

equivalent to the quantity of light perceived by the eye. It determines how light or dark things are.

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The L and M cone outputs are differenced to form a red-green signal, which carries informationabout the relative excitations of the L and M cones. If the L cones are more excited than the Mcones, the red-green difference signal swings to the red direction and vice-versa.

Another, yellow-blue signal is derived from the difference between the red-green signal andthat of the S cones. It works similarly as the other one. If S cones are relatively more exited thanthe L and M cones, the yellow-blue signal swings to the blue direction and vice-versa.

Figure 5: Schematic representation of basic signal forming on the retina [19].

Those types of signals continue via the optic nerve to the brain. Each optic nerve has about1.2 million nerve fibers, which is much fewer than there are rods and cones in the eye. This meansthat a lot of individual signals from neighboring rods and cones are combined together into onezone signal.

IN THE BRAIN

This multitude of signals reaches the brain about 25 times per second. The primary visual

Figure 6: Schematic representation of human brain and its processing of visual signals andinformation [11].

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input arrives in the striate cortex (visual cortex, V1) in the occipital lobe at the back of the head.It is commonly accepted that from there two streams continue through the brain. The ventralstream (“what pathway”) travels to the temporal lobe, which is associated with object recognitionand form representation, and the dorsal stream (“where pathway”) travels to the parietal lobe,which is associated with guidance of actions and space comprehension. The perception of color,among other things, forms and is used in all of these areas in the brain and is essential to humanunderstanding and interpretation of the outside world.

4. Colors

The notion of color is natural way of distinguishing between different wavelength spectra oflight detected with eyes.

4.1 Appearance of Colors

Each single wavelength of light in visible spectrum of sunlight is perceived as a particular color.These so-called spectral colors and their wavelengths can serve as rudimentary definition of a givencolor. All colors together form white light, but taken apart, they form a rainbow-like spectrum.The whole visible spectrum, with wavelengths from 390nm to 740nm, is divided in most obviouscolors: From violet (from about 390nm to about 440nm), through blue (from about 440nm toabout 500nm), cyan (from about 500nm to about 520nm), green (from about 520nm to about570nm), yellow (from about 570nm to about 590nm), orange (from about 590nm to about 630nm),to red (from about 630nm to about 740nm) at the far end. With regards to wavelength, beyondred light of the spectrum is infrared light and under violet light is ultraviolet.

Figure 7: Color spectrum of visible light; from about 390nm (left) to about 740nm (right).

In reality, the perception of colors is quite ambiguous: one perceived color can be composedof a single wavelength, but the same color can also be composed of a certain combination ofvarious wavelengths. This phenomenon is called metamerism. Furthermore, some combinationsof wavelengths can even form colors that are unlike any of the monochromatic, single wavelengthcolors.

PROPERTIES OF COLORS

The abstract properties of colors, which are destinguishable by humans, are hue, saturationand brightness.

Figure 8: Schematic representation of physical aspects of color properties on the spectrum [10].

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Hue is basically the name of the color. It describes how much particular color is similar toor different from unique colors, such as red, yellow, green and blue. In pure spectral colors, huecorresponds to wavelength, but some hues (such as magenta) cannot be represented by a singlewavelength.

Saturation can be described as colorfulness of a color relative to its brightness. Fully saturatedor intense color has no mixture of white, gray or black. Color with no colorfulness, not saturatedor dull, is gray. Spectral colors, and some non-spectral colors as well, are considered to be fullysaturated. Some hues are perceived to be less saturated than others, although in reality they arenot.

Brightness of a colored surface depends upon the degree of its illuminance and reflectivity. Itis the perceived luminance of an object. Colors can be perceived as light or dark.

COLOR MIXING

Primary colors are three colors in widely spaced regions of visible spectrum that can be mixedtogether in equal intensities to produce white color. Most commonly used primary colors arered, green and blue. They broadly represent three cone types in human eye. These colors are usedin additive color mixing. The principle of additive mixing is to add primary colors of certainintensities to the color mixture. By additively mixing red, green and blue in varying intensitiesmost of the visible colors can be reproduced. When all primary colors are mixed in equal intensities,the result is white; when none, the result is black. The physical example for this kind of mixingcould be three overlapping spotlights of primary colors in a dark room.

If two primary colors are mixed together in equal intensities, secondary colors emerge. Theseare yellow (green + red), magenta (red + blue) and cyan (blue + green). They can be used insubtractive color mixing. The principle of subtractive mixing is, in a way, to remove certaincolors of certain intensities from the color mixture. In this way also, most of the visible colors canbe reproduced. If two secondary colors are mixed together in equal intensities, the original primarycolors emerge: red (magenta + yellow), green (yellow + cyan), blue (cyan + magenta). When allsecondary colors are mixed in equal intensities, the result is black; and when no secondary colorsare present, the result is white. The physical example for this kind of mixing could be three whiteoverlapping spotlights each with a filter of secondary color.

White color can also be produced by mixing so-called complementary colors, one primary andone secondary. The pairs are: red and cyan, blue and yellow, green and magenta.

Figure 9: Schematic presentation of additivecolor mixing [7].

Figure 10: Schematic presentation of subtractivecolor mixing [7].

Several color models and mathematical color spaces have been developed to make the distinctions,measurement and reproduction of colors easier. Color space or color model or color system is

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an abstract mathematical description of the way colors can be represented as a set of specifiednumbers, known as color components. We shall take a look at the most common and the mostuseful of color systems.

4.2 CIE Color Space

CIE 1931 XYZ color space was one of the first mathematically defined color spaces and wasinvented by Commission internationale de l’eclairage. This is commonly used standard and also abasis for many other color spaces.

Since human eye has three types of cones for seeing in well-lit conditions, in principle, threeparameters can describe the sensation of color. This tristimulus values can be, for example,intensities of three primary colors in additive color mixing, discussed above. The tristimulusvalues in CIE 1931 XYZ color space are X, Y and Z. They are, in a way, derived parameters fromred, green and blue colors.

To make CIE 1931 XYZ color system as objective as possible, CIE has defined the so-calledstandard colorimetric observer. This standard observer is characterized by three color matchingfunctions x(λ), y(λ) and z(λ), which are numerical description of chromatic response of theobserver. They are actually spectral sensitivity curves of three linear light detectors that modelthe standard observer and were measured experimentally.

With color matching functions tristimulus values X, Y and Z for a certain color can be derived,if spectral power distribution I(λ) of this color is known:

X =

∫ ∞0

I(λ)x(λ) dλ (2)

Y =

∫ ∞0

I(λ) y(λ) dλ (3)

Z =

∫ ∞0

I(λ) z(λ) dλ, (4)

where λ is the wavelength of light.

Figure 11: The three color matching functions x(λ), y(λ) and z(λ) in CIE XYZ color system [9].

Because there are three tristimulus values, the plot of visible colors is tree-dimensional.To simplify things, the concept of color can be determined only by brightness and chromaticity1.

1Chromaticity is an objective specification of a color, determined by its hue and saturation, regardless of itsbrightness.

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In CIE XYZ color space the parameter Y is the measure of brightness of a color. Chromaticity ofa color is specified by two newly derived parameters x and y, which are just normalized values oftistimulus values:

x =X

X + Y + Z(5)

y =Y

X + Y + Z(6)

z =Z

X + Y + Z. (7)

It is obvious that x + y + z = 1. This, a bit modified color space with parameters x, y and Y isknown as CIE xyY color space. The original tristimulus values can be calculated back like so:

X =Y

yx (8)

Z =Y

y(1 − x− y). (9)

New parameters make it possible to draw a CIE 1931 color space chromaticity diagram intwo dimensions: x and y. It is a tool to specify how humans experience light with a particularspectrum. The color of any light-emitter can be completely and unambiguously defined by x andy coordinates. But the color appearance of any passive, non-emissive, reflective of transmissive

Figure 12: CIE XYZ color space chromaticity diagram. Triangle inside the CIE XYZ diagramrepresents a lesser sRGB color space. The black line in the middle represents the color of a black

body at a given temperature [12].

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material can be defined by x and y coordinates only under a certain source of illumination. That isbecause the color appearance of such passive materials is related to the spectral power distributionof the light source. If some colors are missing from the light source spectrum which is illuminatinga passive material, those colors will be missing from the passive material spectrum as well.

The outer curved boundary of CIE chromaticity diagram is spectral locus and representsmonochromatic light of spectral colors. The lower straight boundary of the locus is the line ofpurples and represents non-spectral colors, obtained by mixing light of red and blue wavelengths.The edge of the diagram, therefore, includes all of the perceivable hues. Colors on the edge of thelocus are saturated; colors become less and less saturated towards the middle of the plot, wherethe color is white. This achromatic point at x = y = 1/3 represents the white light, perceived froman equal-energy flat spectrum of radiation. The diagram is convex in shape.

The colored area of the plot is also called the gamut of human vision, since it represents all ofthe chromaticities visible to the average person.

All the colors that lie in a straight line between two arbitrary points (which are actually colors)on the gamut can be formed by mixing these two colors. Furthermore, all colors that can beformed by mixing three colors are found inside the triangle formed by the source points on thechromaticity diagram; and so on for even more sources.

Interestingly, three real sources of colorful light cannot cover the entire gamut of human vision.Because the gamut of human vision is not a triangle, no three points within the gamut can bechosen that would form a triangle which would includes the entire gamut.

4.3 HSL Color Model

HSL color model is another way to describe color with 3 parameters. HSL stands for hue,saturation and luminance. It was designed to be very intuitive, to define colors more naturally.Hue specifies the base color, other two values specify the saturation of that color and how brightthe color is.

The HLS color model is geometrically represented by a double cone.

Figure 13: Representations of HSL color space; lower left is view from the top [13], [14].

In this model, hue is represented by the angular perimeter. Hues are arranged around the

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circumference of the base circle, where each hue has its own specified angle; for example: 0◦ - red,60◦ - yellow, 120◦ - green, 180◦ - cyan, 240◦ - blue, 300◦ - magenta.

The top and bottom ends of two cones, also called the apexes, are the colors of white andblack, respectively. They are directly connected by a vertical axis in the center of both cones. Thedistance from each of the two apexes is what represents the lightness of brightness in this colormodel. Lightness has values between 0%, black, and 100%, white. With lightness at 50% percent,the color is deemed pure.

The saturation in HSL color model is graphically viewed by the radial distance from the axis.The values run from 0% to 100%. At 0% there is no color, as this represents the axis of the cones,which is a grayscale. At 100% saturation a given hue is fully saturated at a given percentage ofillumination.

HSL color model is a sort of expansion of more crude and not so intuitive RGB color model.

4.4 Reproduction of Colors

Color models are also the essential component in reproduction of colors. They define in whatratios and intensities must three or four basic colors be combined to recreate a given color. Themost widely used are the additive RGB color model and the subtractive CMYK color model.

RGB COLOR MODEL

The RGB color model is an additive model in which the base colors are red, green and blue.They are additively combined, as has been described above, in various ways to reproduce varietyof other colors. The RGB color space is the color space used by computers, televisions and similarelectronic systems that emit light. It is a convenient color model because the human visual systemworks similarly - though not exactly the same.

The three colors are mixed by varying their intensities. The tristimulus values R, G and Bare therefore the intensities of these three base colors. If all three are mixed at 100% intensity,the result is white, and if they are all at 0%, the three colors are absent and the result is black.Because all three base colors are equal in importance, a three dimensional cube can be drawn torepresent the RGB color space. In this cube each dimension is represented by the intensity of oneof the base colors.

Figure 14: RGB color space, as viewed from opposite sides (left). The frame and the grayscalebody diagonal of the RGB color space (right) [15].

Since the color in color space can be thought of as a vector, it can be also mathematically

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written as one:Color = RR +GG +BB (10)

if R, G and B are unit vectors of the RGB color space.The coordinates (R,G,B) for some more familiar colors are: (0, 0, 0) - black, (1, 0, 0) - red,

(0, 1, 0) - green, (0, 0, 1) - blue, (1, 1, 0) - yellow, (1, 0, 1) - magenta, (0, 1, 1) - cyan, (1, 1, 1) - white.The grayscale line is represented by the body diagonal of the cube, from (0, 0, 0) to (1, 1, 1).

RGB displays have relatively small gamut compared to CIE 1931 XYZ color model, whichrepresents all of the human perceivable colors.

CMYK COLOR MODEL

The CMYK color model is a subtractive model in which the base colors are cyan, magenta,yellow and black (also called key). It is ideal for color printing, especially on white surfaces, wherethose colors serve as filters for reflected light. CMYK color printing uses the principle of subtractivecolor mixing, as has been described above. Contrary to the RGB color model, in CMYK colormodel the absence of any color is white and the presence of all of them is black.

Figure 15: Schematic representation of CMYK color model used in printing.

Addition of black, to cyan, magenta and yellow in this color model, was mainly done foreconomic reasons in printing: it is cheaper and easier to darken the image with pure black, ratherthan with the combination of all of the other three. CMYK printers often have a relatively smallcolor gamut, which means that not all perceivable colors can be reproduced on paper with thistechnique.

5. Conclusion

Although colors do not exist in physical nature, they are very important for humans, andpossibly other living creatures as well, to observe the world around them. The special notionof colors, their relations, differences and similarities help humans every day to understand andinterpret objects, appearances, occurrences and events that are or that happen within the eye’sreach. They also help in orientation, navigation and nourishment of humans...

That is why colors have always been in the interest of human science and culture. While thecultural aspect of colors has been strong for millennia, the scientific and mathematical aspect ofcolors has just barely emerged a couple of centuries ago. Though color science is relatively young,it is quite successful and is already highly developed in various models and systems.

Most of the biological, physical and chemical processes of color perception are known and wellresearched. The last and illusive part of the complete understanding of human color perceptionhides in the human brain. It is not yet perfectly clear how exactly it processes and interprets allof the signals it receives from the eyes. That mystery is yet to be completely discovered.

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Page 15: seminar - 4th year PERCEPTION OF COLORSmafija.fmf.uni-lj.si/seminar/files/2010_2011/Perception_of_Colors... · seminar - 4th year PERCEPTION OF COLORS Author: Jernej Lalo s Mentor:

Seminar Perception of Colors Jernej Lalos

6. Literature

[1] K. R. Gegenfurtner and L. T. Sharpe (editors), Color Vision; From Genes toPerception (Cmabridge University Press, Cambridge, 2000).

[2] V. Golob, Barvna metrika (Tiskarna tehniskih fakultet, Maribor, 2001).[3] R. A. Meyers (editor), Encyclopedia of Physical Science and Technology; Volume 3

(Academic Press, San Diego, 2002).[4] R. Tilley, Colour and Optical Properties of Materials (John Wiley & Sons,

Chichester, 2000).[5] http://de.wikipedia.org/wiki/Farbe (2.5.2011).[6] http://en.wikipedia.org/wiki/Color (2.5.2011).[7] http://hyperphysics.phy-astr.gsu.edu/hbase/vision/visioncon.html#c1 (2.5.2011).[8] http://webvision.med.utah.edu/ (2.5.2011).[9] http://fr.wikipedia.org/wiki/CIE XYZ (2.5.2011).[10] http://graphics.cs.cmu.edu/courses/15-463/2010 fall/Lectures/CapturingLight.ppt

(2.5.2011).[11] http://cmp.felk.cvut.cz/∼hlavac/TeachPresEn/15ImageAnalysis/

61HumanEyePhysiology.ppt (2.5.2011).[12] http://en.wikipedia.org/wiki/Color vision (2.5.2011).[13] http://en.wikipedia.org/wiki/Hsl color space (2.5.2011).[14] http://ocaml.xvm.mit.edu/ xsdg/stuff/gimp/hsl-doublecone.png (2.5.2011).[15] http://www.industrial-needs.com/technical-data/colour-meter-pce-rgb.htm (2.5.2011).[16] http://en.wikipedia.org/wiki/Sunlight (2.5.2011).[17] http://courses.washington.edu/psy333/lecture pdfs/Week2 Day1.pdf (2.5.2011).[18] http://mb-faculty.mosesbrown.org/anewbold/AP%20Bio/powerpoint/

Structure%20and%20Function%20of%20the%20Human%20Eye.ppt (2.5.2011).[19] http://cs.haifa.ac.il/hagit/courses/ist/Lectures/IST04 ColorOpponentx4.pdf

(2.5.2011).

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