Color measurement instrumental

Instrumental color measurements eliminate subjectivity, are more precise, take less time, and are simpler to perform. However, to evaluate instrumental results properly, the physics of the measurement processes must be considered. Three types of color measurement instruments are used for food the monochromatic colorimeter, the tristimulus colorimeter, and the colorimetric spectrophotometer. 

Color measuring instruments, 7 323-326 Color-order systems, 7 308-311, 325-326 Color perception, 7 303-304 Color photographic products, 19 197 Color photography, 19 231-272. See also Chromogenic materials additive, 19 284 additive mixing in, 19 240-241 dye stability in, 19 263... 

F.W. Billmeyer, Jr., and P.J.Alessi, Assessment of Color-Measuring Instruments for Objective Textile Acceptability Judgement, Natick Technical Report TR-79/044, U.S. Army Natick Research and Development Command, Natick, MAs, 1979. 

The American Public Health Association (APHA) also developed a method for evaluating the color of wastewater. Initially, this method was used as an indication of water purity and involved making comparisons of test samples with dilutions of a 500-ppm Pt-Co stock solution. In the APHA index system, distilled water is assigned a value of 0 (zero) and the stock Pt-Co solution has a value of 500. Details pertaining to the preparation of solutions and sample measurements are provided in ASTM D1209-93. In addition, ASTM D1209 describes how to correlate data from color measurement instruments with data from physical APHA and Pt-Co color standards. 

Color measuring instruments are superior to the human eye as regards the ability to differentiate between chroma and hue. The trained eye is, however, superior to color measuring instruments in the evaluation of differences between full shade colors and dark colors. If paint has to satisfy stringent color limits, final pass-fail decisions are made on the basis of visual inspection instrumental color measurement serves only as an aid [9.28]. 

A color measurement instrument can be used as a tool to record the lifecycle of any color. The goal is to maintain the integrity of a color from design through implementation to production to final assembly and delivery. In the automotive field a color begins life at the design table, where a color or concept of colors is determined that will enhance a specific car or line. This would be an excellent point to capture a color measurement, because chances are the color may never be the same again. 

Color measurement requires the determination of the spectral distribution of the light reflected from the surface. In continuous color measurement, usually a limited number (e.g., three) of spectral regions are determined by measurement across a filter. Various commercial color-measuring instruments, colorimeters and spectrophotometers, are available today [33], including systems for monitoring continuous webs. These systems automatically provide data on color, opacity, and yellowing at one or several user-selected web locations. 

Another route to stable high-reflectance standards is the use of ceramic tiles or white glass materials. Such materials are usually used only in the visible region of the spectrum due to absorbances shown by the pigments in the UV and NIR. Typically, the tiles are a ceramic baked onto a metallic substrate, with the white pigment usually being titanium dioxide. Such standard materials are provided by Erie Ceramics and the OMH. These standards are used heavily in the color measurement instrumentation in which durability is the key factor in their selection. A similar standard, under the appellation of SRM-2019, has been provided by NIST for use in the... 

VIS-NIR region of the spectrum (Fig. 5). White glass materials, commonly known as opal glass —the most familiar of these are the so-called Russian Opal (also known as MS-20 milk glass) and Japanese opal glass—are also frequently used by manufacturers of color measurement instrumentation (Fig. 6). 

Fig. 4. Lrft) Schematic of the MCS 2 x 512 VIS color-measuring instrument, consisting of two identical spectrometer modules and the movable measuring head with integrating sphere and flash tube. Right) Measuring setup for the thickness measurement of films and layers, consisting of light source, diode array spectrometer, and fiber bundles (38).

Evaluation of Color - The color of a finished coating may be qualitatively evaluated by visual comparison to an established standard using appropriate test panels. Most color comparisons, however, are being made quantatively by measurement of the test panels on color measurement instruments which calculate color coordinates and determine the color difference. 

ASTM D2244, Methodfor Calculation of Color Differencesfrom Instrumentally Measured Color Coordinates, Vol. 6.01, ASTM, Philadelphia, Pa., 1989. 

With the best observing conditions, it is possible for the trained observer to compete with photoelectric colorimeters for detection of small color differences in samples which can be observed simultaneously. However, the human observer cannot ordinarily make accurate color comparisons over a period of time if memory of sample color is involved. This factor and others, such as variability among observers and color blindness, make it important to control or eliminate the subjective factor in color grading. In this respect, objective methods, which make use of instruments such as spectrophotometers or carefully calibrated colorimeters with conditions of observation carefully standardized, provide the most reliable means of obtaining precise color measurements. 

The science of color measurement has been explored by various authors (127,128). AATCC evaluation procedure no. 6 describes a method for instrumental measurement of color of a textile fabric. AATCC evaluation procedure no. 7 may be used to determine the color difference between two fabrics of a similar shade. Instrumentation may be either a spectrophotometer for measuring reflectance versus wavelength, or a colorimeter for measuring tristimulus values under specified illumination. If a spectrophotometer is used, however, the instrument must be equipped with tristimulus integrators capable of producing data in terms of CIE X, Y, and Z tristimulus values. 

The instrument used in colorimetry is called colorin eter it determines and specifies colors by referring to other colors. This process will permit,by the proper selection of suitable reagents, the identification of principle ingredients in the sample tested when it is in solution. The depth of color, measured by the colorimeter, gives the quantity of material present in a solution. This is known as colorimetric analysis (See also Color... 

The development of the observer response functions is the foundation for color measured by an instrument. The Standard Observer established a recognized method for converting... 

Color scientists continue to propose newer color-difference equations. New models of color instruments are being introduced almost every year. The world of color analysis is adapting to the scientific advances that shape food technology and many other areas. Color measurement is still founded on basic principles that confirm the important relationship between the human eye and the instrument. Spectrophotometers and colorimeters assist the eye rather than replace the eye. A properly maintained color instrument is a great asset to a colorist with a trained eye. 

The science and methods of colorimetry have been reviewed as a system of color analysis. The color measurement concludes successfully when the instrument data agree with the visual evaluation. The color data from the instrument provide a consistent, objective, and documented way to evaluate color. However, the final color analysis is the judgment made... 

In the direct competitive ELISA, the analyte specific antibodies are first coated on a solid phase. The sample or standard solution of analyte is generally incubated simultaneously with the analyte enzyme conjugate or incubated separately in two steps. The amount of enzyme bound to the plate is then determined by incubation with a chromogenic substrate solution. The resulting color/fluorescence, which is inversely proportional to the analyte concentration present in the sample, is then measured instrumentally or by visual comparison with the standards. 

Wirth M. Instrumental color measurement a method for judging the appearance of tablets. J Pharm Sci 1991 80(12) 1177—1179. 

Initial inspection of the dyed carpet suggested that good color reproducibility and uniformity had been achieved. Ten samples were cut from each of the dyed samples and the color measured on the Diano Colorimeter. Each sample was measured three times to average variations due to instrument changes and sample texture differences. Tristimulus values (X,Y,Z) were calculated from the average of the three measurements. 

In addition to instrumental color measurements, the dyed carpets have been examined visually by four experienced carpet dyehouse supervisors. All four agreed that both the nylon and polyester carpet dyeings were acceptable as first-quality in both color uniformity and color reproducibility. 

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