Color measurements primary colors

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. 

A strict definition of color includes (1) the object appearance that depends on light, object, and observer, and (2) the visual perception described with color names. Color is a primary attribute of appearance and it can be quantified. The measurement of color is known as colorimetry. The colorimetric principles associated with the response of the normal eye are important when reviewing color analysis. The eye-brain combination is sensitive, flexible. 

A third measure uses the three-color theory to establish that all colors Z can be decomposed from at least three primary colors, which we can arbitrarily choose as R = red (4 = 700 nm), G = green (1 = 546.1 nm), B = blue (4 = 435.8 nm) ... 

Color is a significant feature of visual images. The quality of color can be characterized in terms of the decomposition of a color signal into three primary components. Usually these components will be red, green, and blue, the primary colors, measured by their luminance. Alternatively, color components could include the hue, luminance, and value components. 

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. 

Primary and secondary amines Reaction with 1-fluoro-2,4-dinitrobenzene Reaction with 1,2-naphthoquinone-4-sulfonate lO- -iQ- moir A fluoride-selective electrode is used. Measurement of color formation in the presence of Triton X-100... 

A block copolymer consisting of three AnB ,An blocks. The instrument for color measurement based on spectral tristimulus values. The color is expressed in terms of three primary colors red, green, and blue. 

The tristimulus filter colorimeter was apparently developed in order to retain some of the advantages of the spectrophotometer and at the same time to decrease the labor needed to calculate the numerical specifications of color. They are generally more portable than the spectrophotometers, cost less, and require much less interpretation of the results. All of the data of the tristimulus colorimeters can be interconverted to any of the standard systems of color measurement. Their accuracy depends upon the fit between the theoretical response of the C.I.E. primaries and the response achieved by the combination of light source, filter, and photocell. The fit is in no case perfect, and is usually worst in the small lobe of the X primary. 

In all apphcations of color measurement, the primary objective is to produce a color data history close to the originally perceived color situation (1-3). Practicing this idea is key to successful color measurements. Human color perception varies with individuals but is second nature to all of us in every conceivable situation. Most of this section is devoted to some of the practical problems and solutions of color measurements based on this circumstance. 

In this study, color measurement (delta E) has been chosen as the method to evaluate extent of scorch. This method of evaluation should be carefully considered as color development can result from several very different sources. Actual degradation of the PUR foam is the primary concern and probably contributes the majority of measured discoloration. Discoloration can also result from the highly colored transformation products of phenolic antioxidants. Discoloration from BHT transformation to quinones has been widely studied. 

The primary instrument used to measure color is the human eye. This is a very subjective method for evaluating color, as each person differs in sensitivity to the various colors of the visible spectrum. Some 8% of the population, mostly male, have a color deficiency or color blindness. In addition to color deficiencies in the viewer, other variables can cause variation in the perceived color. These were mentioned previously and include the illumination source and the surroimd color (i.e., the color of the background against which the specimen is viewed). 

To summarize, let us look at some of these terms again. Spectroscopy means to look at the spectmm, but not necessarily the visible, nor even the electromagnetic, spectrum. There are emission, absorption, visible, ultraviolet, infrared, nuclear magnetic resonance, and mass spectroscopies—this is the broadest term of all and this is not an exhaustive list Spectrometry means HteraUy to measure the spectrum, and we can apply the word to all the types of spectroscopies named above. Spectrophotometry means literally to measure the spectrum with photons, and so can only include those types of spectrometries thatutiUze photons in this term. Even more particular is colorimetry, which means literally to measure color, a term that can be ambiguous because it includes (1) a form of spectrophotometry and (2) a color measurement system based on color primaries for color-matching. 

From the above discussion, it is clear that given a CIE standard source, object, and spectral tristimulus values, one can easily measure color. The instrument developed for such color measurement is called a tristimulus colorimeter. A tristimulus colorimeter measures color in terms of three primary colors red, green and blue, or more properly stated, in terms of three tristimulus values. Many different color scales have been developed to describe the color numerically in terms of lightness and hue. One of the most widely accepted systems is known as the L, a, b tristimulus system. Figure 6-10 illustrates L, a, b color space. The coordinate L is in the vertical direction and corresponds to lightness. A perfect white has an L value of 100 and a perfect black a zero. The variables at and bt identify the hue... 

Color plays a special role in the foods we eat. For example, when confronted with a food of an unattractive color, the consumer assumes the food is of poor quality or is spoiled. Similarly, a product with an atypical color, e.g., a green cheese or a blue drink, in most cases would be rejected by the consumer. Typically, one associates certain colors with certain food items such as cherry with red, lemon with yellow, and orange with carrot. Therefore, color can serve as a primary identification of food and also as a protective measure to prevent the consumption of spoiled food. Food colors create physiological and psychological expectations and attitudes that are developed by experience, tradition, education, and environment we inevitably eat with our eyes. ... 

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. 

Figure 7.7 Peptide spot color intensity as a function of doubling dilutions of primary (PR) antibody. PR peptides and PR+ tissue sections were both placed on the same slides and stained with various dilutions of the PR mAb. Color intensity of the peptide spots (square symbols) or tumor cells (triangle symbols) was measured and plotted on the y-axis. The figure shows a linear decline in intensity with decreasing antibody concentrations for both the peptide spots and the tissue sections. Tissue color intensity is measured as optical density on a 0-2 scale. Peptide spot color is measured as mean pixel intensity on a 1-256 scale. Copied with permission from Sompuram et al.6...

Figure 13.2. TOF-SIMS images of blue (m = 413 u) and green (m = 641 u) pigments of color filter array. Above each image the primary ion gun and the measurement time is displayed. Corresponding signal intensity of emitted secondary ions from an analyzed surface is given under suitable image. (Reprinted from Kollmer, F. 2004. Appl. Surf. Sci., 231-232 153-158. With permission from Elsevier.) (See color insert.)...

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