Color primary colors

Color cannot be measured because it is perceived in the brain. However, it can be specified instrumen-tally using additive or subtractive mixing to produce a color that matches the object color. In the former, a match to most colors can be made by the additive mixing of light of the three primary colors. A measure of the intensity of the three primaries provides a specification of the color. Primary colors are defined such that none can be matched by mixtures of the other two. The principle of additive mixing is the basis of the common tristimulus and spectrophoto-metric methods of measurement. 

The diisobutyrate ester of trimethylpentanediol is an economical, low color primary plasticizer for use ia surface coatings, vinyl flooring, moldings, and other vinyl products. This diester is commercially available from Eastman as Kodaflex TXIB plasticizer (49). 

In colored cathode ray tubes (CRTs), such as those used in televisions and computer terminals, three electron gun beams are focused on three different sets of phosphor dots on the front face of the tube. The dots are produced by using a compHcated photoHthography process. The phosphor dots are produced by settling the three different phosphors, each of which emits one of the primary saturated colors, red, green, or blue. Each phosphor is deposited separately and the three dots in each set are closely spaced so that the three primary colors are not resolved at normal viewing distances. Instead the viewer has the impression that there is only one color, the color achieved when the three primary colors are added together. 

Olfactory receptors have been a subject of great interest (9). Much that has been postulated was done by analogy to the sense of sight in which there are a limited number of receptor types and, as a consequence, only three primary colors. Thus attempts have been made to recognize primary odors that can combine to produce all of the odors that can be perceived. Evidence for this includes rough correlations of odors with chemical stmctural types and the existence in some individuals having specific anosmias. Cross-adaptation studies, in which exposure to one odorant temporarily reduces the perception of a chemically related one, also fit into this hypothetical framework. Implicit in this theory is the idea that there is a small number of well-defined odor receptors, so that eventually the shape and charge distribution of a specific receptor can be learned and the kinds of molecular stmctures for a specified odor can be deduced. 

Color and Color Separation. In 1860,James Clerk MaxweU discovered that all visible colors could be matched by appropriate combinations of three primary colors, red, green, and blue (RGB). His experiment involved mixtures of colored lights added together to produce other colors or white light. This additive color is weU represented by the primaries RGB. Indeed, human color vision is trichromatic, ie, human visual response approximates receptors for the colors recognized as red, green, and blue (see Color). 

Color Mixing. The various types of dye powders used to make dye stains are blended to achieve the desired color. Most finishers purchase wood stains premixed to specified colors. In the wood-finishing industry, various shades of brown are the most common. These colors are usually blended from primary colors. Color-matching skills can be acquired only by practice, but the basic theory of color matching is relatively simple and easily understood. The basic theory of color matching can be demonstrated by using the color circle shown in Figure 1 (see Color). 

In color technology and measurement, both types of approaches are used. Color printing, for example, generally employs three colors (usually plus black), and the ever useful CIE system was founded on experiments in which colors were matched by mixtures of three primary colors, often blue, green, and red. Yet transmitted television signals are based on the opponent system, with one intensity and two color-balance signals, as are the modern representations of color, such as the CIELAB and related color spaces based on red-green and yeUow-blue opponent axes. 

The GIE Standard Observer. The CIE standard observer is a set of curves giving the tristimulus responses of an imaginary observer representing an average population for three primary colors arbitrarily chosen for convenience. The 1931 CIE standard observer was deterrnined for 2° foveal vision, while the later 1964 CIE supplementary standard observer appHes to a 10° vision a subscript 10 is usually used for the latter. The curves for both are given in Eigure 7 and the differences between the two observers can be seen in Table 2. The standard observers were defined in such a way that of the three primary responses x(X),jy(X), and X), the value ofjy(X) corresponds to the spectral photopic luminous efficiency, ie, to the perceived overall lightness of an object. 

The dyes used in the ink sheet must satisfy various requirements (/) optimum color characteristics of the three primary colors (hue, color density, shape of absorption spectmm) (2) sensitivity, ie, sublimabiHty from ink sheet to acceptor sheet (3) fastness for light and migration and (4) compatibiHty with the resin in the ink sheet. With respect to these characteristics, a large number of anthraquinone dyes have been proposed particularly for magenta and cyan colors. Typical examples are given in Table 8 and Table 9. 

Several basic chromophore stmctures have been proposed for this purpose. Anthraquinone dyes appear to be predominant since they have a wider color range, excellent photostabiHty, good solubiHty in Hquid crystal media, and very high order parameters. Typical basic stmctures of the three primary colors are illustrated in Figure 11. Some examples are given in Table 10. The appropriate combination of three primary colors gives a black display. 

Fig. 11. Basic stmctural concepts for the three primary color anthraquinone Hquid crystal dyes.

Dyes for Color Filters. Colorhquid crystal display systems consist of LSI drivers, glass plates, polarizers, electrodes (indium—tin oxide), and microcolor filters. The iadependent microcolor filter containing dyes is placed on each Hquid crystal pixel addressed electrically and acts as an iadividual light switch. All colors can be expressed by the light transmitted through each filter layer of the three primary colors, ie, red, green, and blue (Fig. 12). 

Stamm-farbe, /, primary color = Stamman-satz, -flotte, /. (Dyeing) stock liquor, stock solution. 

Colorimeter Also called color comparator or photoelectric color comparator. An instrument for matching colors with results about the same as those of visual inspection, but more consistent. Basically the sample is illuminated by light from the three primary color filters and scanned by an electronic detecting system. It is sometimes used in conjunction with a spectrophotometer, which is used for close control of color in production. 

If we wish to match colors, the primary colors are quite different, as shown in the following ... 

The difficulty in setting up the initial system for color comparisons cannot be underestimated. The problem was enormous. Questions as to the suitability of various lamp sources, the nature of the filters to be used, and the exact nature of the primary colors to be defined occupied many years before the first attempts to specify color in terms of the standard observer were started. As we said previously, the Sun is a black-body radiator having a spectral temperature of about 10,000 °K (as viewed directly from space). Scattering and reflection... 

Once we have done this, we now have our three primary colors in the form of standard lamps, and can proceed to determine Items 1,2 3, given above on page 421. To do this, we vary the wavelength of the monochromatic light, and determine relative amounts of red, green and blue light required to match the monochromatic color. This is done, as stated before, for about 5000 observers. 

When we mix these primary colors, their reflectances remove more of the ineident light, and we see the part where the reflectances are reinforced. Ihus,... 

Synthetic food colorants offer the primary colors (red, green, bine) and others offer yellow and orange. The food, textile, and cosmetic indnstries continne to need wider ranges of shades and hnes. These can be obtained by the process of colorant blending. 

Primary clay is also known as residual clay, indicating that they are either the in situ residue of one type of weathered rock or the transported residue of many types of rocks most primary clay deposits occur, however, in situ, at the location where the clay particles were formed. The clay is usually quite pure and colorless or white, but very small relative amounts of minerals mixed with the clay, such as quartz and/or iron oxides, may impart to it a yellow, brown, or green color. Primary clay is also characterized by the extreme fineness of its particles, which usually measure below 2 micrometers (0.002 mm) in diameter. The more than 20 different types of primary clay minerals can be distinguished by their chemical composition, which varies widely, and by their physical properties. Primary clays that have been used for making ceramic objects are listed in Table 55. 

Primary clay, for example kaolin, is colorless, and when such clay is heated to a high temperature it produces white ceramic materials. Most pottery, however, is colored its color is due to the fact that most of it was, and still is, made not from primary but from secondary clay. Secondary clay contains minerals other than clay, and colored metal ions in them endow the pottery with their color. Iron ions (in iron oxides), for example, tend to make pottery yellow, brown, or red, and manganese ions (in pyrolusite, a mineral composed of manganese oxide) make it either dark or black. 

Although several schemes have been developed for the quantitative expression of color [38], only the CIE (Commission Internationale de l Eclairage) system has gained general acceptance [39], This system assumes that color may be expressed as the summation of selected spectral components in a three-dimensional manner. The three primary colors normally added for such purposes are blue, green, and red. The CIE system is based on the fact that human sight is trichromatic in its color perception, and that two stimuli will produce the same color if each of the three tristimulus values (X, Y, and Z) are equal for the two ... 

The A(A), y(A), and z(A) terms were derived by the CIE from data obtained in visual experiments where observers matched colors obtained by the mixing of the blue, green, and red primary colors. The average result for human observers were defined as the CIE 1931 2° standard observer, and the wavelength dependencies of these color-matching functions are illustrated in Fig. 6. 

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