Color measurements tristimulus values

The science of color measurement has been explored by various authors (127,128). AATCC evaluation procedure no. 6 describes a method for instmmental 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. Instmmentation 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 instmment must be equipped with tristimulus integrators capable of producing data in terms of CIE X, Y, and Z tristimulus values. 

Fabric Color Change The color of the aged samples was assessed with a General Electric Recording Spectrophotometer which measures tristimulus values X, Y and Z and reflectance. Color difference ae in NBS units (AN 40 units) was calculated using the Adams-Nickerson color difference formula (H) ... 

Objective color measurement is based on tristimulus colorimetry. " This instrumental method measures tristimulus values of light transmitted by a sample and compares the results to the values transmitted by distilled water. The results can be recalculated to the platinum-cobalt scale referred to in the previous standards. The results can also be interpreted by normal methods of color measurement to yellowness index, color, color depth, etc. 

Since many paint layers already exhibit inhomogeneities in such dimensions for the calculation of color data (tristimulus values and chromaticity coordinates), it is necessary to use mean reflectance values derived from three to five individual measurements of different sample areas. For individual measurements, the sample surfaces, especially in the case of paints containing plate-Hke pigments (light interference and/or color variable pigments), should have varying orientations to the adjustable measuring aperture. 

The most successful quantitative expression of color is that known as the CIE (Commission Internationale de l Eclairage) system [13]. This methodology assumes that color may be expressed as the summation of selected spectral components (blue, green, and red hues) in a three-dimensional manner. 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. Detailed summaries of the CIE and other quantitative systems for color measurement are available [14,15],... 

In Eqs. (7)—(10), 5(A) is the spectral power distribution of the illuminant, and R A) is the spectral reflectance factor of the object. Jc(A), y(A), and 5(A) are the color-matching functions of the observer. In the usual practice, k is defined so that the tristimulus value, Y, for a perfect reflecting diffusor (the reference for R A)) equals 100. Using the functions proposed by the CIE in 1931, y(A) was made identical to the spectral photopic luminous efficiency function, and consequently its tristimulus value, Y, is a measure of the brightness of objects. The X and Z values describe aspects of color that permit identification with various spectral regions. 

Colors specified in terms of the tristimulus values X, Y, and Z are fairly hard to visualize. For this and other reasons, a variety of different color systems have been devised. The color coordinates in these systems can be calculated from the X, Y, and Z values, which are of central importance to color measurement because of their close link to measurable quantities. 

They are represented as coordinates in a color plane. The chromaticity coordinates x and y are used to specify the saturation and hue of any color in the CIE chromaticity diagram. See Figure 4 a for illumination D 65. The CIE spectral tristimulus value y (2) corresponds to the lightness sensitivity curve of the human eye. Therefore, a third color variable is specified in addition to x and y, namely the CIE tristimulus value Y, which is a measure of lightness. 

Methods of Determination. Lightness. The white pigment powder is compressed in a suitable powder press to give an even, matt surface. The CIE tristimulus value Y is measured with color measuring equipment. For standards, see Table 1 ( Lightness ). Apparatus spectrophotometer or tristimulus colorimeter, powder press, white standard. 

The measurement of color on tristimulus colorimeters will depend on the type of machine and its operating instructions. It should be noted that orange juice color readings are affected by incorporated air and by variations in temperature. The juice should be deaerated and brought to 80°F i 2° before readings are made. Color value readings will have to be correlated with visual evaluations to be meaningful. 

Color measurements on Parylene-C film were determined with a Minolta Chromameter 221, a colorimeter with output limited to CIE chromaticity or tristimulus values and CIELAB L, a and b color coordinates. Measurements on the films after various exposure times were recorded with the sample mounted over the white calibration plate. 

Reproducibility of the dyeings was determined by calculation of the color differences between dyed lots and a standard dyeing of the same shade. In this calculation the color difference was determined from average tristimulus values of each dyed lot compared to a conventional dyeing, again using the FMC II equation. In addition to instrumental measurements, samples dyed by the reuse procedure were examined visually by expert dyers to further assess the color uniformity and color reproducibility. 

The dyed nylon batches were evaluated by color measurement and color difference calculations using the described procedure. Ten random samples were cut from each of the five nylon carpet sections (3 x 38 ) dyed in the reuse sequence. Color differences between the samples from the four reuse runs and samples for the initial (conventional) dyeings were calculated. The tristimulus values and 1 were obtained on the Diano... 

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. 

By creating scales for hue, lightness, and chroma, we can now measure color numerically. Other methods for expressing color numerically were developed by the Commission Internationale de l Eclairage (CIE), an international organization concerned with light and color. The two most widely known of these methods are the Yxy color space, devised based on tristimulus values XYZ defined by CIE, and... 

Instrumental Color Measurements. When treated samples showed AATCC ratings of 4 or less, they were measured against the untreated samples on the Sargent-Welch SP8-200 UV-vis spectrophotometer with a diffuse reflectance sphere attachment. The instrument is interfaced with a Hewlett-Packard HP-85 computer and run by color measurement software. Spectral reflectance data at 10-nm intervals, tristimulus values, chromaticity coordinates, and CIELAB color difference were determined for these samples (21). 

Color The color of the film can affect the consumer acceptance of coated produce (60). Five different color systems XYZ, Yxy, L a b, L C H° and Hunter Lab are used to express absolute chromaticity. Color system XYZ is measured as tristimulus values of color and forms the basis for most calculations. In the color system Yxy, Y is a lightness factor expressed as a percentage based on a perfect reflection of 100%. x and y are chromaticity coordinates defined by the following equations ... 

We finally arrive at the result we want, since we can now set up Tristimulus Filters" to use in defining colors. We can now define "y as our standard luminosity curve for the human eye (photopic vision). Note that X, the red tristimulus value, has a certain amount of blue in it in order to duplicate the response of the red preceptor in the retina. Note that these colors are the result of the "Standard Observer" measurements that we started in the first place. 

The three different color-response mechanisms in the human eye are the scientific basis for the measurement of color that is standardized in the Cl E Standard Observer (1931). This system specifies color according to X, Y, Z tristimulus values and. v. , z chromaticity coordinates. Several alternative scales were subsequently developed to provide a better adaptation to the color differentiation ability of the human eye [9.26]. 

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. 

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