Color - SpeedyLook encyclopedia

Definition

The whole of the colors is defined, currently, very often by its three characteristics of color, value and saturation. The LaB system tends to replace it in the advanced colorimetric systems. On the chromatic circle, one finds: complementary colors, let us tons hot and cold, of the colors known as secondary, the primary colors, and the values (white and black)

The whole of the frequencies of the light waves forms the spectrum colors (often called spectrum of the colors) energy of the Infrarouge S with the Ultraviolet S.

It has only two values there. The white and black. The gray, which is colors of the white and black, are however colors, and not values.
One names “dyes” the frequencies generating the chromatic impression. In nonexperimental situation, several frequencies always coexist, but they have as a resultant dominant chromatics.
One names “value” the luminous amplitude defining the color; the closer it is to the Noir, the more the value is low.
One names “saturation” the promptness (purity) of a color, and by opposition, one calls desaturation, his mixture, more or less important, with a Gris of the same value.

The “Gris” are particular values on the axis black-white. It is always about a mixture (in additive Synthèse) of equal proportion and with the same value of the three primary colors Rouge, Vert and Blue. In subtractive Synthèse the three colors would be the Cyan, the Jaune and the Magenta.

Each one of the gray can be regarded as a color deprived of color; the black and the white are gray extremes. The black is a gray of zero value and corresponds to the absence of any light (no light is received by the eye). The white is a gray of maximum value and can be regarded as a plenitude of colors (the whole of the frequencies of light wave is received the eye with a maximum value). Let us note that in any rigor, there does not exist a white, but an infinity of white, of which each one is characterized by its temperature of color : photography-colors and in video, one usually distinguishes the white with approximately: 2800 K (Kelvins) of a traditional Lamp incandescent, it: 3200 K of a lamp Photoflood with tungsten, it: 5200 K of a Arc lamp and it: 6000 K of a electronic Flash or Sun.

Additive synthesis

The principle of the additive synthesis of the colors consists in endeavouring to reconstitute, for a human eye, the equivalent (appearance) of any visible color, by the addition, according to quite selected proportions, lights coming from three monochromatic sources (for example of the spots) of which the wavelengths are selected once and for all to meet this aim as well as possible.

By observing the rainbow, one can see that the droplets of rain, in the distance, break up the light six colors, as prisms would do it.

Newton reproduced this phenomenon by breaking up solar light thanks to an optical prism (a right prism out of glass at triangular base). It succeeds in breaking up the white light all the various colors of the spectrum.

The physicist Young made the opposite of Newton. He recomposed the light. He made converge the six colors of the spectrum and obtained the white light. He was even further showing than the six colors of the spectrum could be reduced to three. I.e. it could recompose the white light with these three colors. It also showed that by mixing them two by two, it could obtain the others.

And thus one differentiated the primary colors from the secondaries.

This system of mixture of lights means that more one adds colors more one obtains clearness. For example, the green and the red give the yellow unquestionably more clearly. One speaks in this case about additive system.

In theory, these three optimal wavelengths, that one calls primary colors, are those, completely saturated, whose colors correspond to the maximum of sensitivity of the three types of cells in the shape of cone which paper the retina of a normal human eye (thus unfulfilled Daltonisme or another dyschromatopsie).

The three primary colors are the following ones:

red primary;
Green primary;
Blue primary.

All this corresponds to what is called in French the system Rouge blue green (RVB) or in English Red Green Blue (RGB).

There exists many other systems related to the RVB which results from work of the International commission of Lighting. The basic system is Co XYZ, from where one deduces the Co xyY which separates brightness and the chrominance. This last gave rise to many practical systems of which more used is undoubtedly the Co Lab which comprises the yellow in addition to the red, the green and blue.

System RVB also can, in an equivalent way, being expressed according to three other components which are the color, the value and saturation and correspond in French to the system TSL ( T einte, S aturation and L uminosity or value) and in English with system HSL (according to the three English words Hue , Saturation and Lightness ).

There exist mathematical formulas making it possible to pass from three components RVB to three components TSL (and conversely).

One names lights of primary colors (sometimes called secondary colors) the lights of colors saturated obtained by mixing two to two and with equal shares the lights with primary colors.

The complementary colors are the colors which, combined, contain all the colors of the spectrum and no jointly.

The three secondary colors in the additive system are:

Cyan (lights green and blue, complementary to the red);
magenta (lights red and blue, complementary to green);
Yellow (lights green and red, complementary to blue).

who are in fact the primary education colors of the subtractive system and gives the system CMJ (in English CMY or YMC).

When one mixes more than two primary educations, one désature the color. It thus loses in saturation and gains in value, to approach the white.

Subtractive synthesis

In Printing works - colors, Painting and in the art of the Stained glass, there cannot be some discussion about adding with the colors by mixture of light, but rather of colors pigments.

All the opaque bodies, when they are lit, reflect a part or all the light which they receive and absorb the remainder. One can thus obtain the colors of the spectrum either by mixing pigments or by filtering part of the spectrum which lights the object.

The pigments which mix absorb light more and more and become increasingly dark. For example the yellow and the magenta give the orange red one.

One speaks in this case about subtractive Synthèse. And in this case the primary colors, also called primary colors associated to differentiate them from the primary education colors from the additive system because they correspond to the secondary colors of the additive system.

Cyan fundamental;
magenta fundamental;
Yellow fundamental.

give the system CMJ (in English CMY or YMC).

In theory, and if we have perfect pigments, the use of the three fundamental ones would make it possible to obtain:

the Blue by mixing the Cyan and the magenta ;
the Green by mixing the Cyan and the Yellow ;
the red by mixing the magenta and the Yellow .

In practice, the subtractive synthesis starting from the current dyes does not make it possible to obtain the whole of the visible colors by the human eye. Moreover, even of the perfect dyes would continue to pose problem because they are often added in a chemical reaction which deteriorates the final color.

Indeed, when two coloured materials are mixed, one obtains the wished color well from it, but this one loses in promptness, and the addition of white to compensate for this loss is not satisfactory because the white désature dyes it and thus does not allow to obtain the required value. For this reason several ink jet printers of ink add two colors pastel to the three fundamental ones in order to obtain the best returned.

Lastly, a black obtained by the mixture of the three fundamental ones would be at the same time expensive (mixture of three expensive inks) and of doubtful quality (because the superposition is never perfect, nor opacity). In printing works, one thus uses always at least the black like fourth color , which corresponds to the Quadrichromie, used for all that is printed color.

Let us add that in impression of large surfaces (posters, for example), the technique of the screens of impression makes it possible to circumvent the question: indeed, if one examines a poster of close, one realizes that the colors are juxtaposed there much more often than they are not superimposed on it. One then finds something of very similar… to additive synthesis. However, this process is generally not usable for current illustrations like that of a magazine.

Problems in painting

In painting, one will prefer to take more basic colors, because even if the cyans, magentas and yellows used are very sharp (very important value), they lose of their promptness while mixing, which could limit the pallet of the artist.

Let us retain that in subtractive synthesis (using Pigment S), contrary to the additive synthesis, the mixture of more than two colors does not denature those, and mixes it several colors systematically makes him lose in value.

Another problem which can emerge is that of the chemical stability of the pigments. Sometimes, the mixture of a pigment and another product a compound of a different color, deteriorating the result. The kinetic of the chemical reaction can prevent from realizing of the problem immediately: for example, one can mix white and red to obtain a pink agreeing with the skin, and the two pigments react in a few months to form a black compound which wastes the table. From where importance of chemistry in the choice of the colors.

Physiological principle of the color

The decomposition of the color by the human systems red, green and blue, is especially due to the fact that it is the 3 colors to which the 3 types of cones are best adapted which are used for the reception of the color in the human eye (the Bâtonnet S are rather sensitive to the intensity of the light):

the cones L, sensitive to the long waves (700 Nm), therefore the reds
the cones M, sensitive to the medium waves (546 Nm), therefore the greens
the cones S, sensitive to the short waves (436 Nm), therefore blue the

Methods subtractive and additive

The subtractive calculation of the colors (or subtractive Synthèse) is the calculation made by withdrawal of some wavelengths of the light, and thus on what is not source of light.

For example, the grass or the sheets of the trees appears green to us, because they absorb complementary to green, i.e. purple and ultraviolet ones. These are these waves that they use in the Photosynthèse.

The additive calculation of the colors (or additive Synthesis) is the calculation made by addition wavelengths of sources of light.

For example, If the two components green and red of a monitor of computer are lit, the colors of associated phosphorus (juxtaposed) superimpose because of the bad resolution of the eye, and a yellow color is obtained, which is solved again in green and red if one looks at this zone of the screen through a Compte-fils or by reflection on a cédérom. It is easy to try out that with the adjustments of the colors of the office of your computer (if it is not monochromic). The synthesis of chestnut requires appreciably more tests (council: test on the basis of purple, as against-intuitive one as that appears).

Table of colors

Colors métamères, a function of the eye

How can one reconcile the two phenomena exposed higher? On a side, the study of the decomposition of the light teaches us that the pure colors are monochromatic, that the green has its characteristic wavelength, blue has another characteristic wavelength, and yellow, another still. On another side, the additive mixture of two colors such as the green and the red produce a third, the yellow of it. Are the wavelengths modified? Not, at all.

To explain the feeling produced by the mixture, it is necessary to call upon the physiology of the eye. The sensitive cells of the retina, the cones, transform any radiation of visible light into three nervous impulses of variable values which are forwarded to the brain. Even a monochromatic light like the green is in this way coded by its 3 values.

However it is that the retina is unable to make the difference between the yellow monochromatic light and the sum of the two lights green and red, because its cones are in the same way excited, and send the 3 same nervous impulses in both cases.

In other words, physically the two lights are different, because their spectral composition is different. On the other hand, the impression for the eye is the same one.

Luminous whole of different composition spectral which produces the same impression coloured on the eye is called colors métamères .

Difference in colors

Generally

The difference between two colors for the human eye, can vary according to people, and sometimes even very slightly between the two eyes of the same person (one can then realize by blinking it). A difference, which does not appear obvious for the majority of people will be able to appear null for somebody reached of Daltonisme or on the contrary enormous for somebody who is accustomed to compose of the colors the every day, like a painter or a printer. As an indication, the tapestry makers distinguish five hundred nuances from red.

In subtractive synthesis, colors appearing identical to two people under a white of a given temperature (for example light of day) will be able to appear different to them under a white from another temperature. For this reason, the system that one hoped for universal Cube of Hicketier, and which would have associated with each color a single number, did not have a continuation.

Bizarrery

One of the 500 patents deposited by the doctor Edwin H. Land, creator of instantaneous photography (Polaroïd) relates to a process reduced of restitution of all the spectrum, starting from only two basic colors, which goes against our current knowledge on the mechanism of the vision. It should be noted that this patent, unlike much of other inventions of Land, led in practice to no realization.

Solution suggested

That thus poses problems of reference, which would be used to check a certain equivalence, between two colors differentiated by their support and medium. The Colorimétrie thus tries to solve these various problems. One finds in particular in the system Co L*a*b* the concept of Delta E the difference between two colors (Lab 1 and Lab 2).

The language of the colors

To each color of the characteristics were allotted, even of the properties. The language of the colors is however not universal and changes according to the times.

In some langues example? )-->, several names can be given to the same color according to the context, in others, one usually symbolizes a whole of colors by a generic name: for example, Inuits have 17 words to indicate the white whereas the Icelanders use the same word for the green and blue while at the same time the Breton ones adjectives to indicate the various colors of the sea and sky have (dyed gray-blue with the green-lichen, with various intensities).

Examples:

the red , is red orange, Vermillon, magenta Carmin or ? (the tapestry makers have 500 distinct references of red)
the Bleu is Navy blue, overseas, cobalt , clearly or Cyan?

In addition, the Symbolique of the colors seems to carry major invariants at the same time as it varies at the surface level according to the Cultures. For example, the white represents the Pureté in Occident and the Deuil in Asia. But what seems contradictory is actually identical, indeed mourning in Asia is lived like a stage of access to the purity, which returns the white to the same requirement for purity as well in the East as to occident.

In France, the color of mourning is often associated with the black. However, the white was also a color of mourning, in particular that of the queens of France (cf e.g. Marie Stuart).

To marry in white to evoke a so-called virginal purity goes back only to the end of the 18th century: previously, married was to wear its more beautiful dress and during several centuries, for the European country class, this dress was red, color of the joy, the festival and the pleasure.

The color is one of the important subjects of concern of the visual Sémiotique.

See too

References

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