Hunter colorimeter

Change In total color, determined by Hunter Colorimeter, Model D25M-9. d Color value, Hunter Colorimeter, Model D25M-9. 

Solution color refers to the yellowness of the cellulose acetate solution. The most meaningful measurement is the yellowness index (YI) for an 18% solution of cellulose acetate in 9/1 methylene chloride methanol (by weight). Measurement is made by the Hunter colorimeter described above. Hemicelluloses in the pulp affect the color of the solution of cellulose acetate, but there are other factors that relate to solution color including brightness of the wood pulp and cellulose acetate processing conditions. 

Reflectance meters such as tristimulus colorimeters measure colour on the basis of the amount of light reflected from the surface of the fruit (Kader 1985). Several types of tristimulus colorimeters are available that measure the colour of fruit depending on lightness, red to blue tone and yellow to green tones. Two common types are the Hunter Colorimeter system and the various Minolta Chroma Meters (CR-300 series), both types use the L, a, b coordinates (Brown and Walker 1990 McGuire 1992). 

In addition to fiber length, strength, and fineness, two other properties that have significant bearing on fiber and yam properties are color and trash measurements, which are measured by instmmentation such as the Nickerson-Hunter Colorimeter (64) and the Shirley Non-Lint Analyzer (65). 

Rockwell and Rao show data comparing C12 SME and Cl3.6 SME to LAS and SLS via detergency testing [30]. hi the article they explain that these are commercial products and not pure SME samples. They do contain some sulfonated fatty acid as an active surfactant. The testing was accomplished in a Terg-O-Tometer with 1 L of wash liquor and the delta reflectance represents the difference in reflectance units of the L reading of the Lab scale via a Hunter Colorimeter. Rockwell demonstrated poorer performance of the C12 SME in... 

Measurement of Whiteness. The Ciba-Geigy Plastic White Scale is effective in the visual assessment of white effects (79), but the availabihty of this scale is limited. Most evaluations are carried out (ca 1993) by instmmental measurements, utilising the GIF chromaticity coordinates or the Hunter Uniform Color System (see Color). Spectrophotometers and colorimeters designed to measure fluorescent samples must have reversed optics, ie, the sample is illuminated by a polychromatic source and the reflected light passes through the analy2er to the detector. 

Colorimeters. Also known as tristimulus colorimeters, these are instniments that do not measure spectral data but typically use four broad-band filters to approximate the jy, and the two peaks of the x color-matching functions of the standard observer curves of Figure 7. They may have lower accuracy and be less expensive, but they can serve adequately for most industrial color control functions. Examples of colorimeters are the BYK-Gardner Co. XL-835 the Hunter Lab D25 series the Minolta CA, CL, CS, CT, and CR series (the last of these is portable with an interface) and the portable X-Rite 918. 

The R,G,B values of the Berger formula measured by tristimulus colorimeters are linearly related to the X,Y,Z tristimulus values of the CIE system. The Stensby formula incorporates the L,a,b tristimulus values of the Hunter system. In the CIE 1982 formula, x and yn are the chromaticity coordinates of the D65 (2° or 10° observer) light source. 

For most other purposes, both before and after processing, color is measured using a colorimeter such as a Minolta Chroma Meter (Minolta Corp., Ramsey, NJ). The instrument is calibrated against a standard-white (Minolta) reference plate. Hunter L (whiteness), a (greenness) and b (yellowness) values were determined for each sample and made directly from the potato surface (Nourian et al., 2003). 

Huggart (17) using a Hunter Citrus Colorimeter developed an equation containing CR and CY values which established a high correlation between instrument color values and U. S. Department of Agriculture visual color scores. The State of Florida... 

Photoelectric colom measuring instruments can be divided into two classes, trichromatic colorimeters and spectrophotometers. The most successful of the early trichromatic colorimeters was developed in the 1940s by Hunter (1958). It comprised a light somce and three wideband red, green and blue filters to approximate CIE standard illuminant C and the 2° observer. The tristimulus values obtained were transformed into Hunter L, a, b colom space. Until the advent of the computer and the photodiode such... 

In a tristimulus colorimeter, three or four filters duplicate the response of the standard observer. The filters, which correspond to the three primary colours in the spectrum (red, green and blue), can be combined to match most colours. The more sophisticated instruments carry a fourth filter to simulate the blue part of the CIE [[X bar]] function shown in Fig. 5.1. The other essential parts of a tristimulus colorimeter are a white light source, an array of photometers and, nowadays, a computer or an interface to one, as shown in Fig. 5.2a. The computer can collect responses as well as carry out data transformations between CIE and other colour scale systems or between different standard white light sources or white diffusers. Hunter and Harold (1987) give a good summary of the transformation formulae employed. Data from a colorimeter is given as a three-point output, commonly CIELAB, HunterLab or 7, x, y. 

A section of 10 g of bacterial cellulose was cut into 1 cm sections to measure color appearance. The values of L, a, and b were measured by a Hunter Lab Color Quest (Memmert, Germany) colorimeter with the CIELAB color system. These values were then used to calculate chroma (C ) and hue angle (/lab) values. L indicates lightness, with a scale ranging from 0 (black) to 100 (white). Positives and negatives in a represent red and green, whereas positives and negatives in b represent yellow and blue, respectively. 

Many commercial colorimeters utilize variants of the Hunter 1958 (Lab) space. The coordinates are ... 

NIST total color difference n. The total color difference, AE, calculated by means of the NIST color difference equation, sometimes referred to as a Judd or a Judd unit. The term is frequently erroneously used to refer to the color difference calculated by other equations normalized to agree in magnitude on the average to an NBS unit, or to the AE measured on tristimulus colorimeters with electrical circuits designed to give an approximation of the NIST color difference equation, frequently one of the Hunter E a, b equations. Such incorrect use of the term is to be discouraged. Description of the exact equation and method of measurement used will avoid confusion (NIST, www.nist.gov). 

The Hunter tristimulus colorimeter represents a departure from the usual colorimeters, as it presents its data in a form closely akin in spacing to the Munsell system. By resistance networks between a series of barrier-layer photocells which view the reflected light from a specimen through tristimulus filters and a compensating cell which views the light source, a reading is obtained which is related to perceptible differences. 

If the Hunter colour difference meter (Model D25A-2, F,STH,H, Hunter Associates Laboratory) is used, it employs 45° diametrically opposed illumination and a 6.4-mm viewing aperture. Due to the directional nature of the colorimeter illumination and small colour variation within the designated surface area, each fruit should be rotated 90° on axia, and a second within the same area should be averaged with the first (Delwiche and Baumgardner 1985). 

The method relies on the instrumental measurement of the degree of yellowness under daylight illumination of close to colorless or close to white translucent or opaque plastics. The measurement is made on pellets and is based on the tristimulus values that are obtained with a colorimeter. Methods are provided to determine the color measurements, such as yellowness index, CIE X, Y, Z, and Hunter L, a, b, or CIE L, a, b. A series of specimens that is compared should have similar gloss, texture, etc. 

Once washed, the swatches are read on a Hunter Lab Colorimeter for reflectance (L), redness/greenness (a), and yeUowness/blueness (b) values. The reflectance is used to calculate percent soil removed (% SR) which ranges from 0 to 100. Whiteness index (Wl) [17] and yellowness index (Y2) can also be determined. The whiteness scale ranges from 0 (black) to 100 (white). The yellowness index ranges from positive (yellow) to negative (blue). To determine how much soil is removed from the fabric, see Figure 2. 

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