This is the chat log of the seminar, but before that – some links which can help you to expand your knowledge on the topic and generally can be helpful for your further work:
http://www.cs.brown.edu/courses/cs092/VA10/HTML/start.html
http://colortheory.liquisoft.com/
http://www.color-wheel-pro.com/color-theory-basics.html
http://kuler.adobe.com/
The log has been edited.
=======================================================
You: I have promised you since long time a seminar on Color theory
You: But Color is such a vast subject that i decided not to call it this way after all ;p
You: Because even though we will talk quite a bit about color theory per se, we will also need to mention Color spaces and Color Models, which are being in a way related to the Color theory, still stand apart
You: In the arts of painting, graphic design, and photography, color theory is a body of practical guidance to color mixing and the visual impact of specific color combinations.
You: Color theory is a vast, complicated and controversial subject, and it’s virtually impossible to cover all its aspects in one seminar, that’s why i placed some links in the materials folder here.
You: You can open these links and see if you would like to keep some of them open at the time of our seminar for reference
You: In a nutshell all the debates around color theory rotate around 1 question: what is color and how do we interpret and measure it.
You: Many researchers compared colors to sound, and for a reason. Both deal with human perception, making them both subjects of philosophy as much as natural sciences.
You: Aristotle looked at color appearing in nature as reflection of LIGHT, as the color of sunrise and sunset, as the color of fire seen through the veil of smoke. In other words, as a reflection of LIGHT sent by God to human eye.
You: Even here in SL, looking at your computer screen we see light emanating from it, and here, too we have our virtual sunsets and virtual sunrises, we can even change the color of SL sun if we want, but it’s essential property remains light.
You: And so the fundamental notion of of color and light arises.
You: In the view of this, it seems to make a lot of sense to begin our discussion with understanding the concept of additive and subtractive color mixing..
You: Painters mix their paints to shape the light reflected from a painting, and the viewer’s eye interprets this reflected light as color.
You: These two extremes of color experience — the mixed paints, and the interpreting eye — are described by two separate and unequal color mixing theories.
You: Isaac Newton’s hue circle (seen on the pic here) -
You: the first modern explanation of color mixing, was a geometrical arrangement of the different colors seen in the solar spectrum.
You: Newton suggested that the chromaticity (hue and saturation) of a light mixture could be predicted as the weighted average of the ingredient hues around the hue circle.
You: This is the original statement of additive color mixing.
You: As implied by the averaging method, in additive color mixture all wavelengths of light add to a total color effect, so that the color of lights always determines the color of their mixture.
You: At the same time, Newton explicitly stated that color is a perceptual property, not a physical property, which meant that the weighting of wavelengths in a light mixture occurred in the eye, not in the light.
You: Today we attribute the chromaticity of light mixtures to the relative stimulation (separate from brightness) induced in the 3 cones of the retina (we will talk about the human eye anatomy in a few moments).
You: However, artists deal with colored substances such as paints or dyes, and color mixtures in substances behave differently from color mixtures in the eye.
You: In subtractive color mixing, each substance in a mixture absorbs or subtracts wavelengths from the incident light.
You: However, the color mixture “predictions” made by subtractive color theory are often inaccurate, because the light absorbing properties of a colorant are affected by its physical state, including the other colorants it is mixed with.
You: Additive color mixing explains how the eye interprets light wavelengths in the perception of color.
You: It describes the color structure of light perception, and is the foundation for identifying visual complementary colors
You: and placing colors in the visual color wheel.
You: This pic here is for reference on complimentary colors, which are treated differently by substractive and additive color mixing theories
You: The beauty of additive color mixing principles is in their narrow scope.
You: They are limited to a single physical process for the description of color — the responses of the 3 color receptors.
You: Additive color mixing is a description of the trichromatic basis of color vision and nothing more. (Again we will see about the color receptors in the human eye in a moment)
You: light is the stimulus, and additive color theory is about the response of the eye to that stimulus.
You: So in other words, Additive color mixing is dealing with light as the cause of color perception in the human eye, and substructive color mixing deals with pigments or substances used for creating colors by artists
You: The existence of these 2 theories has made color as such a controversial subject.
You: Painters traditionally have been dealing with substractive colors – pigments or substances
You: .And this brings us to PRIMARY COLORS.
You: The painter’s three primary colors are the foundation of academic “color theory”
You: Color theory was originally formulated in terms of three “primary” or “primitive” colors — red, yellow and blue (RYB) — because these colors were believed capable of mixing all other colors.
You: This color mixing behavior had long been known to printers, dyers and painters, but these trades preferred pure pigments to primary color mixtures, because the mixtures were too dull (unsaturated).
You: The RYB primary colors became the foundation of 18th century theories of color vision, as the fundamental sensory qualities that are blended in the perception of all physical colors and equally in the physical mixture of pigments or dyes.
You: These theories were enhanced by 18th-century investigations of a variety of purely psychological color effects, in particular the contrast between “complementary” or opposing hues that are produced by color afterimages and in the contrasting shadows in colored light.
You: These ideas and many personal color observations were summarized in two founding documents in color theory: the Theory of Colors (1810) by the German poet and government minister Johann Wolfgang von Goethe, and The Law of Simultaneous Color Contrast (1839) by the French industrial chemist Michel-Eugène Chevreul.
You: Subsequently, German and English scientists established in the late 19th century that color perception is best described in terms of a different set of primary colors — red, green and blue violet (RGB) — modeled through the additive mixture of three monochromatic lights.
You: Subsequent research anchored these primary colors in the differing responses to light by three types of color receptors or cones in the retina.
You: On this basis the quantitative description of color mixture or colorimetry developed in the early 20th century, along with a series of increasingly sophisticated models of color space and color perception.
You: Across the same period, industrial chemistry radically expanded the color range of lightfast synthetic pigments, allowing for substantially improved saturation in color mixtures of dyes, paints and inks.
You: It also created the dyes and chemical processes necessary for color photography.
You: As a result three-color printing became aesthetically and economically feasible in mass printed media, and the artists’ color theory was adapted to primary colors most effective in inks or photographic dyes: cyan, magenta, and yellow (CMY).
You: (In printing, dark colors are supplemented by a black ink, known as the CMYK system; in both printing and photography, white is provided by the color of the paper.)
You: These CMY primary colors were reconciled with the RGB primaries, and subtractive color mixing with additive color mixing, by defining the CMY primaries as substances that absorbed only one of the retinal primary colors: cyan absorbs only red (-R+G+B), magenta only green (+R-G+B), and yellow only blue violet (+R+G-B).
You: So in other words applying RGB system cyan is expressed as <0,1,1>
You: Magenta as <1,0,1>
You: and yellow as <1,1,0>
You: It is important to add that the CMYK, or process, color printing is meant as an economical way of producing a wide range of colors for printing, but is deficient in reproducing certain colors, notably orange and slightly deficient in reproducing purples.
You: A wider range of color can be obtained with the addition of other colors to the printing process, such as in Pantone’s Hexachrome printing ink system (six colors), among others.
You: For much of the 19th century artistic color theory either lagged behind scientific understanding or was augmented by science books written for the lay public, in particular Modern Chromatics (1879) by the American physicist Ogden Rood, and early color atlases developed by Albert Munsell (Munsell Book of Color, 1915
You: and Wilhelm Ostwald (Color Atlas, 1919).
http://webexhibits.org/causesofcolor/1B.html
You: Major advances were made in the early 20th century by artists teaching or associated with the German Bauhaus, in particular Wassily Kandinsky, Johannes Itten, Faber Birren and Josef Albers, whose writings mix speculation with an empirical or demonstration-based study of color design principles.
You: Contemporary color theory must address the expanded range of media created by digital media and print management systems, which substantially expand the range of imaging systems and viewing contexts in which color can be used.
You: These applications are areas of intensive research, much of it proprietary; artistic color theory has little to say about these complex new opportunities.
You: So let’s have a bit closer look at modern scientific basics of light and color perception.
You: What is light and what is its origin?
You: The nuclear fusion occuring within the sun produces a massive flow of radiation into space.
You: Scientists describe this radiation both as cycles or waves in an electromagnetic field and as tiny quantum packets of energy (photons).
You: The distance between the peaks in one cycle of an electromagnetic wave is its wavelength (symbol λ) and measured in nanometers (billionths of a meter).
You: The number of wave peaks within a standard distance is the wavenumber, the reciprocal of wavelength (1/λ), which must be multiplied by 10 million to yield waves per centimeter.
You: Light waves increase in frequency (number of cycles per second) as the radiation increases in energy; “short” wavelength, high frequency light has roughly twice the energy of “long” wavelength, low frequency light.
You: Frequency is a constant property of light at a given energy.
You: Both wavelength and wavenumber depend on the refractive index of the medium that the light is passing through.
You: As the refractive index increases, light slows down (travels less distance in unit time), which decreases wavelength.
You: Wavelength numbers are usually standardized on the speed of light in air at the earth’s surface.
You: So for our puposes we can define Light as the electromagnetic radiation that stimulates the eye.
You: This stimulation depends on both energy (frequency, expressed as wavelength) and quantity of light (number of photons).
You: Here you can see the whole spectrum expressed as wavelength
You: The figure shows the visible spectrum on a wavelength scale, roughly as it appears in sunlight reflected from a diffraction grating (such as a compact disc), which produces an equal spacing of light wavelengths.
You: (A rainbow or glass prism produces an equal spacing of wavenumbers, which compresses the “blue” end of the spectrum.)
You: Outside the visible range, electromagnetic radiation at higher energies (wavelengths shorter than 380 nanometers) is called ultraviolet and includes xrays and gamma rays.
You: Lower energy radiation (at wavelengths longer than about 800 nm) is called infrared or heat; at still lower frequencies (longer wavelengths) are microwaves, television waves and radio waves.
You: Notice the very gradual falloff in luminosity at the near infrared (IR) end of the spectrum, and the relatively sharper falloff toward ultraviolet (UV).
You: Please don’t mix that up with UV vectors of divisional surfaces
You: At the earth’s surface, the absorbing effects of the the ozone layer and lower atmosphere significantly filter short wavelength radiation below 450 nm and block all radiation below 320 nm.
You: In addition, most wavelengths below 500 nm are blocked from reaching the retina by a transparent yellow color in the adult lens and a pigment layer on the retina.
You: But in noon daylight there is as much energy in long wavelength (heat) radiation as there is in light, so the gradual falloff in perceptible “red” light is due to weaker visual sensitivity in longer wavelengths.
You: Thus, the range of light wavelengths is somewhat arbitrary.
You: Within the spectrum, the spectral hues do not have clear boundaries, but appear to shade continuously from one hue to the next across color bands of unequal width.
You: This is a very interesting table translating hues into wavelengths expresses in nanometers
You: light itself has no color.
You: Color is fundamentally a complex judgment experienced as a sensation.
You: It is not an objective feature of the physical world — but it is not an illusion, either.
You: A single wavelength of the spectrum or monochromatic light, seen as an isolated, bright light in a dark surround, creates the perception of a recognizable hue; but the same light wavelength can change color if it is viewed in a different context.
You: For example, long wavelength or “red” light can, in the right setting, appear red, scarlet, crimson, pink, maroon, brown, gray or even black!
You: Similarly, in all the diagrams or illustrations of color vision , spectrum colors are only symbols for the different wavelengths of light.
You: One of the most important aspects of color psychology emerges when we’re asked to make judgments of color similarity.
You: If we think in terms of the visible spectrum, it seems obvious that yellow and green are more similar than red and green: “yellow” light is closer to “green” light in the spectrum band.
You: Spectral closeness seems a reasonable way to judge the similarity among colors.
You: But ask yourself, which hue is more similar to red: green, or purple?
You: Although purple is at the opposite end of the spectrum from red, most people would answer that purple and red are more similar.
You: Why?
You: Because of the way color information is coded by the eye.
You: The extreme “blue violet” end of the spectrum seems also to contain some “red” light.
You: However, magenta and red violet, the bridging hues between red and blue violet, are not spectral lights.
You: They CAN NOT BE FOUND ANYWHERE IN THE SPECTRUM created by a prism or rainbow, even though “red” and “blue” light, when combined, produce those colors.
You: Vision and color are at the heart of painting.
You: All visual art for that matter
You: and surely our work when we design for displaying images on computer monitor
You: And we have just seen how impossible it is to discuss color and light without relating them to vision.
You: I have mentions color receptors a few times already, and so please, forgive me if i am going to get a bit too scientific now and digress into biochemistry and neurophysiology, but you will see for yourselves how some concepts from these sciences can help you to understand and see color perception much clearer
Aiyanna Sodwind: Katya, question, as you just said we relate color to vision, as an artist I also relate color to what I can feel from it, is the research in that area?
You: es, Aiyanna. This is the whole science of its own and not just one aspect of science
Aiyanna Sodwind: TY
You: these things are studied both by philosophy, Psychology and psychometrics
You: and this is a very big subject on its own
Aiyanna Sodwind: Great I will be doing lots of research than. TY so much
You: it is interesting how the wavelengths of combination of colors and SHAPES can have a very strong effect on human psyche
You: Well, for example yantras (http://www.sanatansociety.org/yoga_and_meditation/yantra_meditation.htm) in eastern philosophy are supposed to be such calculated shapes with particular color combinations aimed at awakening certain areas of higher mind
You: But yes, one can talk for hours on that topic alone 
You: I didn’t include it in this seminar though
Aiyanna Sodwind: Sorry 
You: np, it was a very good question
You: Sight is the sense organ of radiant power
You: It evolved in relation to solar radiation and the materials that absorb, reflect or refract it.
You: Its sense domain is light, but its capabilities radically influence our forms of awareness, our concepts about the world, and our behavior.
You: Since ancient times the eye has been an icon for our consciousness and seeing the metaphor for intelligence — and with good biological justification.
You: The order Primates, which includes humans, have in common binocular vision and a greatly expanded visual cortex for the processing of visual information.
You: Vision is a primate’s dominant sensory domain.
You: lol, i tried to stuff a lot of info into this slide ;p
You: But you will begin to understand all this more or less as i go
You: The eye is an attractive study for two reasons.
You: It is self contained, which means that all the pieces of the puzzle are found within a single organ.
You: It is also essentially a mechanism, with parts that resemble a camera lens, a daylight filter, an aperture control, and an image sensor.
You: However the true organ of vision is not the eye but the brain.
You: The tissue encapsulated by the eye is an outpost of brain neurons that scans the world and interprets the basic luminance, color, contrast and movement in an optical image.
You: The visual cortex at the back of the brain, in tandem with many other brain areas, does the work of conceptualizing and visualizing the world that seems transparently present before us.
You: The eye is a marvel of biological adaptation to a specific function.
You: In large part this adaptation is successful because it separates visual tasks into four levels of structure: the optical eye, the retina, the photoreceptor cells, and the photopigment molecules.
You: Several parts of the eye act as filters to block short wavelength “violet” light from reaching the retina.
You: The most important of these are the cornea, lens, and macular pigment
You: The lens is the principal source of prereceptoral filtering.
You: Colorless at birth, it gradually yellows and darkens with age: the lens of an 80 year old filters out approximately twice as much short wavelength light as the lens of a 20 year old.
You: The optics of the eye serve one purpose: to focus an image on the light sensitive retina, a paper thin layer of nerve tissue covering most of the inner surface of the eye
You: Cornea is the outer shell protecting the eye
You: and fovea is it’s internal surface
You: the fovea is veiled by a small patch of yellow macular pigment, which appears as a slight darkening of healthy retinal tissue.
You: The macular pigment filters out 25% or more of light between 430 nm to 500 nm.
You: In the average adult, the combined ocular media screen out half or more of incident light at wavelengths below 490 nm and nearly all light below 400 nm.
You: However, prereceptoral filtering varies significantly across age or ethnic groups and across individuals within any group.
You: It has the largest effect under intense light (small pupil size and high photopigment bleaching).
You: Neighboring photoreceptors throughout the retina, but especially in the fovea, interact with each other to interpret color and contrast in the optical image, via the secondary cells with “colorful” names such as midget ganglion and parasol cell.
You: These connector cells group cones and rods into center/surround receptive fields that sharpen edges and contrast based on the relative proportions of stimulation received by all the cells in a group.
You: Finally, the secondary cells transform outputs from the three classes of cone into contrasting opponent channels of color and luminance information.
You: These processing steps occur in the retina, rather than in the brain, because the transformed opponent signals can be transmitted through the optic nerve with much less “noise” or error than the individual cone outputs.
You: Signals from the secondary cells are transmitted through individual nerve tracts that are bundled together as the optic nerve, which exits the eye (along with internal blood vessels) through a hole in the retina and sclera.
You: This creates the optic disc or blind spot, a point in the visual field where there are no photoreceptors.
You: The blind spot occurs in the peripheral visual field, where visual acuity is very poor.
You: (but there are some certain eye excersizes which can expand peripheral vision field)
You: It is not normally noticeable because the mind fills in and completes forms we glimpse in peripheral vision, and in this process fills in the vacant area: outside the foveal field, vision is more of a cognitive construction than an optical report.
You: Vision begins at the third level of scale, the photoreceptor cells.
You: These light receptors are easily the most complex sensory cells we have.
You: There are two basic types :
You: the roughly 100 million rods adapted for dim light and night vision, and the 6 million or so cones that perceive daylight luminance, contrast and color.
You: In the outer segment of the photoreceptor cells is the fourth and smallest level of scale, the photopigment molecules.
You: These are the actual transducers of light, the mechanism that translates light energy into biological response.
You: Each photopigment molecule consists of two parts: a short chromophore (light sensitive) molecule derived from vitamin A (retinal) and a gangly protein backbone (opsin) consisting of seven helical structures joined as a long string.
You: This complex of retinal and opsin molecules is generically called rhodopsin
You: On my board you can see a 3D model of rhodopsin – the dark pic in the middle bottom
You: Each photoreceptor generates a baseline signal through the continuous transport of sodium ions (Na+) out of the inner segment of the cell and the import of potassium ions (K+) from outside.
You: At the same time, sodium ions can enter the outer segment via small pores.
You: The resulting ion imbalance produces a small, steady electric current of about –40 millivolts across the cell body when it is not exposed to light.
You: As a result, the rods and cones produce a continuous signal (the dark current) even when they are not stimulated.
You: To create a nerve impulse, light reduces this baseline photoreceptor current.
You: When the chromophore is struck by a photon of the right quantum energy or wavelength, it instantly changes shape (a photoisomerization to all-trans retinal) which detaches it from the backbone.
You: As a result the opsin molecule also changes shape and in its new form acts as a catalyst to other enzymes in the outer segment, which briefly close the nearby sodium ion (Na+) pores of the cone outer membrane.
You: This changes the baseline electrical current across the cell body, which alters the concentration of a neurotransmitter (glutamate) between the cone synaptic body and the retinal secondary cells.
You: As the number of absorbed photons increases, the secretion of neurotransmitter decreases.
You: Rhodopsins strongly absorb light, which gives them a characteristic dark, opaque color called visual purple.
You: The photoisomerization causes a bleaching from purple to transparent yellow, which allows light to pass deeper into the outer segment and strike photopigment molecules below.
You: After photoisomerization, the pigment is regenerated or reassembled from the bleached components.
You: Less than 1% of the total amount of bleached photopigment in a cone is regenerated each second; yet even during daylight, only about 50% of the photopigment is bleached at any time.
You: This is the transduction process by which the retina translates light energy into nerve impulses: light strikes the chromophore, which detaches from the photopigment, which transforms the backbone, which causes an enzyme chemical cascade, which changes the ion permeability of the cell walls, which alters the electric charge of the cell, which alters its baseline synaptic activity, which changes the pattern of activity among secondary cells in the retina.
You: The entire sequence, from photon absorption to nerve output, is completed within 50 microseconds (millionths of a second).
You: Color appearance is not usually defined by the physical attributes of the stimulus alone, but depends on the surroundings in which the stimulus appears, the adaptation of our eyes, and our recent visual experience.
You: We encounter examples of this every day, and habitually ignore them, because the purpose of our visual experience is not to identify colors but to understand the world.
You: The visual context actually shapes or moulds the color, in the sense that the color must fit into an interpretation of the world.
You: The color is part of a whole.
You: So here we come to color models
You: A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components (e.g. RGB and CMYK are color models).
You: When this model is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), the resulting set of colors is called a color space.
You: However, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with little connection to the requirements of any given application.
You: A color model represents the logical or perceptual relationships among colors of lights or surfaces.
You: From the modern perspective, a color model must meet the following four requirements:
You: (1) a color specification that analyzes every light or surface color into a mixture of fundamental attributes (such as “primary” colors, trichromatic cone responses or tristimulus values, or unique hues);
You: (2) a geometrical framework that locates all the possible colors in relation to each other and to the fundamental attributes;
You: (3) a unique color identifier or color notation (now usually the numerical value of the three colormaking attributes — brightness/lightness, hue and hue purity) for every possible color;
You: and (4) a definition of physical exemplars, specific mixtures of lights or paints, that recreate the measured color perception when viewed within a standard surround under standard lighting conditions.
You: There are two kinds of modern color models.
You: A COLOR ORDER SYSTEM is based on a geometrical or enumerative framework that provides the color notation.
You: The fundamental attributes used in the color specification are “pure” pigments or ideal colors; exemplars are manufactured as pigment recipes in specific media.
You: These systems are common in manufacturing applications based on visual color comparisons under fixed (standard) viewing conditions.
You: A COLOR APPEARANCE MODEL is based on a geometrical framework whose dimensions can be adjusted to represent the color changes caused by different illuminants, illuminance levels and surround contrasts.
You: The color specification is based on color matching functions measured by spectrophotometer; these measurements produce the color notation and identify matching physical exemplars.
You: Contemporary artists’ color wheels are color order systems that show only the hue/chroma relationships as defined in a more comprehensive color model.
You: Now have a look at these pic of color spaces
You: One can picture this space as a region in three-dimensional Euclidean space if one identifies the x, y, and z axes with the stimuli for the long-wavelength (L), medium-wavelength (M), and short-wavelength (S) receptors.
You: The origin, (S,M,L) = (0,0,0), corresponds to black.
You: White has no definite position in this diagram; rather it is defined according to the color temperature or white balance as desired or as available from ambient lighting.
You: The human color space is a horse-shoe-shaped cone , extending from the origin to, in principle, infinity.
You: In practice, the human color receptors will be saturated or even be damaged at extremely-high light intensities, but such behavior is not part of the CIE color space and neither is the changing color perception at low light levels
You: ok, CIE color space, original lab color space
You: In the study of the perception of color, one of the first mathematically defined color spaces was the CIE 1931 XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931.
You: I already explained to you earlier that the human eye has receptors (cone cells) for short (S), middle (M), and long (L) wavelengths.
You: Thus in principle, three parameters describe a color sensation.
You: Any specific method for associating three numbers (or tristimulus values) with each color is called a color space; the CIE 1931 color space is one of many such spaces.
You: The CIE XYZ color space is special, however, because it is based on direct measurements of human visual perception, and serves as the basis from which many other color spaces are defined.
You: Adding a certain mapping function between the color model and a certain reference color space results in a definite “footprint” within the reference color space.
You: This “footprint” is known as a gamut, and, in combination with the color model, defines a new color space.
You: For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model.
You: In the most generic sense of the definition above, color spaces can be defined without the use of a color model.
You: These spaces, such as Pantone, are in effect a given set of names or numbers which are defined by the existence of a corresponding set of physical color swatches.
You: Most people have heard that a wide range of colors can be created by the primary colors red, blue, and yellow, if working with paints.
You: Those colors then define a color space.
You: We can specify the amount of red color as the X axis, the amount of blue as the Y axis, and the amount of yellow as the Z axis, giving us a three-dimensional space, wherein every possible color has a unique position.
You: However, this is not the only color space.
You: For instance, when colors are displayed on a computer monitor, they are usually defined in the RGB (red, green and blue) color space.
You: This is another way of making the same colors, and red, green and blue can be considered as the X, Y and Z axes.
You: And btw this color space model was used for creating sculpited prims in SL
You: Another way of making the same colors is to use their hue (X axis), their saturation (Y axis), and their brightness (Z axis).
You: This is called the HSV color space.
Aiyanna Sodwind: So what is referred to as a color map is really color space?
You: Well, yes and no, it depends on how you define color map, Aiyanna
You: because we can look at color wheels also as a type of color mapping
You: Many color spaces can be represented as three-dimensional (X,Y,Z) values in this manner, but some have more, or fewer dimensions, and some cannot be represented in this way at all.
Aiyanna Sodwind: Ok that makes a lot more sense. TY
You: in the direct sense of word, yes, color spaces are the way of mapping colors, but you know that color maps often are defines as color reference tables etc
You: When formally defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see.
You: This is the most accurate color space but is too complex for everyday uses.
You: Since “color space” is a more specific term for a certain combination of a color model plus a color mapping function, the term “color space” tends to be used to also identify color models, since identifying a color space automatically identifies the associated color model.
You: Informally, the two terms are often used interchangeably, though this is strictly incorrect.
You: For example, although several specific color spaces are based on the RGB model, there is no such thing as the RGB color space.
You: Since any color space defines colors as a function of the absolute reference frame, color spaces, along with device profiling, allow reproducible representations of color, in both analogue and digital representations.
Andre Dix is Online
You: The RGB color model is implemented in different ways, depending on the capabilities of the system used.
You: By far the most common general-use incarnation as of 2006 is the 24-bit implementation, with 8 bits, or 256 discrete levels of color per channel.
You: Any color space based on such a 24-bit RGB model is thus limited to a gamut of 256×256×256 ≈ 16.7 million colors.
You: Some implementations use 16 bits per component, resulting in the same range with a greater density of distinct colors.
You: This is especially important when working with wide-gamut color spaces (where most of the more common colors are located relatively close together), or when a large number of digital filtering algorithms are used consecutively.
You: The same principle applies for any color spaces based on the same color model, but implemented in different bit depths.
You: CIE 1931 XYZ color space was one of the first attempts to produce a color space based on measurements of human color perception and it is the basis for almost all other color spaces.
You: Derivatives of the CIE XYZ space include:
You: CIELUV color space – a modification to display color differences more conveniently, replacing: CIE 1964 U*V*W* Uniform color space
You: CIELAB color space
You: Also related is the CIE 1964 supplementary standard observer, which was based on measurements over a larger field of view (10 degrees) than the 1931 XYZ color space, producing slightly different results.
You: Generic color models
You: RGB, CMYK, HSV, HSL, HSB, YBR and some other
You: i will elaborate on this a bit
You: RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color.
You: Light is added together to create form from out of the darkness.
You: RGB stores individual values for red, green and blue.
You: RGBA is RGB with an additional channel, alpha, to indicate transparency.
You: Media that transmit light (such as television) use additive color mixing with primary colors of red, green, and blue, each of which stimulates one of the three types of the eye’s color receptors with as little stimulation as possible of the other two.
You: This is called “RGB” color space—see also RGB color model. Even though, in reality RGB color space does not exist, but this is the term which is frequently used
You: Mixtures of light of these primary colors cover a large part of the human color space and thus produce a large part of human color experiences.
You: This is why color television sets or color computer monitors need only produce mixtures of red, green and blue light.
You: Other primary colors could in principle be used, but with red, green and blue the largest portion of the human color space can be captured.
You: Unfortunately there is no exact consensus as to what loci in the chromaticity diagram the red, green, and blue colors should have, so the same RGB values can give rise to slightly different colors on different screens.
You: Here i would like to make a little digression which seems relevant at this point.
You: But in reality I just feel that by this point you are ready to fully understand what i am going to say
You: When we work on SL CLOTHING we deal with additive color mixing, but at the same time for reproducing fabric we, in a way, simulate SUBSTRACTIVE color mixing and this notion is important, because the method of using a grayscale layer i teach you was originally borrowed by me from the old artist’s technique of UNDERPAINTING.
You: Aiyanna, and if we have other artists among us today will understand what i mean. But i will explain a bit further about underpainting
You: Underpainting, also called dead coloring, is a lost art.
You: What was once one of the most commonly used techniques in oil painting has fallen into almost total disuse among contemporary painters.
Aiyanna Sodwind: Underpainting is important for the definition of the color placed on top.
You: yep
You: From the beginnings of oil painting, underpainting was an essential stepping stone which permitted the painter to rapidly define composition, lighting and the atmosphere of his work.
You: It was the painter’s guide through an often long and laborious process that allowed him to have a clear vision of the overall sense of the painting although it was usually entirely covered by successive paint layers.
Aiyanna Sodwind: I see why that would work in a computer.
Lizziey Whittenton is Online
You: Technically speaking, it is a relatively simple procedure that consists in painting a monochrome version of the final painting with tempera (used primarily by the Italians ) or oils.
You: The degree of finish varied from school to school and was often also a matter of individual taste.
You: Underpainting was a part of a step by step method that was common practice among European painters.
You: This method subdivides work into distinct stages allowing the artist to concentrate on one aspect of technique at a time.
Aiyanna Sodwind: Very efficient way of painting with oils I might say.
You: So availability of such thing as BLEND modes allows us to approximate our grayscale bumpmaps to underpainting
You: and i find very striking similarity with what we do to underpainting, and also, when in advanced classes we will discuss grayscale and color histograms in relation to blend modes, i will remind you of the controversy of “primary colors” which can have very visible effect and DISADVANTAGE in some cases for the usage of grayscale alone
You: luckily, PS gives us sufficient tools to deal with that
You: So, ok, let’s go back to color spaces
You: Common color spaces based on the RGB model include sRGB, Adobe RGB and Adobe Wide Gamut RGB.
You: CMYK uses subtractive color mixing used in the printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color.
You: One starts with a white substrate(canvas, page, etc), and uses ink to subtract color from white to create an image.
You: CMYK stores ink values for cyan, magenta, yellow and black.
You: There are many CMYK colorspaces for different sets of inks, substrates, and press characteristics (which change the dot gain or transfer function for each ink and thus change the appearance).
You: YIQ was formerly used in NTSC (North America, Japan and elsewhere) television broadcasts for historical reasons.
You: This system stores a luminance value with two chrominance values, corresponding approximately to the amounts of blue and red in the color.
You: It corresponds closely to the YUV scheme used in PAL (Australia, Europe, except France, which uses SECAM) television except that the YIQ color space is rotated 33° with respect to the YUV color space.
You: The YDbDr scheme used by SECAM television is rotated in another way.
You: YPbPr is a scaled version of YUV. It is most commonly seen in its digital form, YCbCr, used widely in video and image compression schemes such as MPEG and JPEG.
You: xvYCC is a new international digital video color space standard published by the IEC (IEC 61966-2-4).
You: It is based on the ITU BT.601 and BT.709 standards but extends the gamut beyond the R/G/B primaries specified in those standards.
You: Recognizing that the geometry of the RGB model is poorly aligned with the color-making attributes recognized by human vision, computer graphics researchers developed two alternate representations of RGB, HSV and HSL (hue, saturation, value and hue, saturation, lightness), in the late 1970s, formally defined and described in Alvy Ray Smith’s 1978 paper “Color Gamut Transform Pairs”.
You: HSV and HSL improve on the color cube representation of RGB by arranging colors of each hue in a radial slice, around a central axis of neutral colors which ranges from black at the bottom to white at the top.
You: The fully saturated colors of each hue then lie in a circle, a color wheel.
You: HSV models itself on paint mixture, with its saturation and value dimensions resembling mixtures of a brightly colored paint with, respectively, white and black.
You: HSL tries to resemble more perceptual color models such as NCS or Munsell.
You: It places the fully saturated colors in a circle of lightness ½, so that lightness 1 always implies white, and lightness 0 always implies black.
You: HSV and HSL are both widely used in computer graphics, particularly as color pickers in image editing software.
You: They are present in PS color picker
You: The mathematical transformation from RGB to HSV or HSL could be computed in real time, even on computers of the 1970s, and there is an easy-to-understand mapping between colors in either of these spaces and their manifestation on a physical RGB device.
You: HSV (hue, saturation, value), also known as HSB (hue, saturation, brightness) is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components.
You: HSV is a transformation of an RGB colorspace, and its components and colorimetry are relative to the RGB colorspace from which it was derived.
You: HSL (hue, saturation, lightness/luminance), also known as HLS or HSI (hue, saturation, intensity) is quite similar to HSV, with “lightness” replacing “brightness”.
You: The difference is that the brightness of a pure color is equal to the brightness of white, while the lightness of a pure color is equal to the lightness of a medium gray.
You: And YBR stands for luminance, normalized red and normalized blue
You: In PS you will encounter many of the color spaces i have mentioned
You: So to summarize all this for our practical purposes: color spaces are not to be confused with color models, and color models are not the same as color MODES we deal with in different file types
You: And if you were wondering what color models mean when you encounter their mention in PS, for example in the gradient editor for noise gradient, i hope your questions were answered
Aiyanna Sodwind: Yes TY, the trouble is remember it all.
You: well, it’s not important to remember as much as to understand
Aiyanna Sodwind: True
You: and in the view of everything i spoke of today, i hope it will be much easier for you to understand many technical aspects of PS
You: But well, i still haven’t been able to find out which exactly color space is used by SL >.>
