Color Analysis – CIE94 (ASTM E with ASTM D). Color Analysis – Hunter (ASTM E & ASTM D). Scope: Hunter Lab and XYZ are standard . This standard is issued under the fixed designation D ; the number 1 This practice is under the jurisdiction of ASTM Committee E12 on Color and. ASTM D Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates.
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ASTM D von A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision asym reapproval.
Adtm standard has been approved for use by agencies of the Department of Defense. As revised init included four color spaces in which color-scale values could be measured by instruments, many of which were obsolete, and the color differences calculated by ten equations for different color scales.
The sections on apparatus, calibration standards and methods, and measurement procedures served little purpose in the light of modern color-measurement technology. The revision published in omitted these sections, and limited the color spaces and color-difference awtm considered, to the three most widely used zstm the paint and related coatings industry.
A previous revision added two new color tolerance equations and put two of the color difference equations from the version in an informative appendix for historical purposes.
It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
ASTM D – COLOR DETERMINATION
Where it is suspected that the specimens may be metameric, that is, possess different spectral curves though visually alike aztm color, Practice D should be used to verify instrumental results.
Each material and condition of use may require speci? Current edition approved May 1, Originally approved in Last previous edition approved in as D — Additionally, the colorimetric spectrometer may also be able to report the underlying spectral data from which the colorimetric data were derived.
Today, while instruments intended for use in color measurements share many common components, UV-VIS analytical spectrophotometers are designed to optimize their use in chemometric quantitative analysis, which requires very precise spectral position and very narrow bandpass and moderate baseline stability.
Colorimetric spectrometers satm designed to optimize their use as digital simulations of the visual colorimeter or as the source of spectral and colorimetric information for computer-assisted color matching systems.
Digital colorimetry allows more tolerance on the spectral scale and spectral bandwidth but demand much more stability in the radiometric scale.
A color difference equation quanti?
Inter-changing the reference and test specimens does not change either the perceived or predicted color differences. Summary of Practice 4.
Color-difference units are computed, from these color-scale values, and approximate the perceived color differences between the reference and the test specimen. Each subsequent color scale based on CIE values has 2 6.
On the other hand, color differences obtained for the same specimens evaluated in different color-scale systems are not likely to be identical. To avoid confusion, color differences among specimens or the associated tolerances should be compared only when they are obtained for the same color-scale system.
There is no simple factor that can be used to convert accurately color differences or color tolerances in one system to difference or tolerance units in another system for all colors of specimens. The CIELAB metric, with its associated color-difference equation, has found wide acceptance in the coatings, plastics, textiles and related industries.
While the CIELAB equation has not completely replaced the use of Hunter LH, aH, bH, this older scale is no longer recommended for other than legacy users, and e2244 therefore included in an Appendix for historical purposes. The CIELAB color-difference equation is also not recommended in asmt practice for use in describing small and moderate color differences differences with magnitude less than 5.
The four more recently de? However, for control of color in production, it may be necessary to know not only the magnitude of the departure from standard but also the direction of this departure. It is possible to include information on the direction of a small color difference by listing the three instrumentally d2244 components of the color difference. The three tolerance equations given here d224 been tested d244 against such data for textiles and plastics and have been shown to agree with the visual evaluations to within the experimental uncertainty of the visual judgments.
That implies that the equations themselves misclassify a color difference with a frequency no greater than that of the most experienced visual color matcher.
Color Analysis – CIE94 (ASTM E1347 with ASTM D2244)
Good correlation with the visual judgments may not be obtained when the d224 are made with other illuminants. Use of a tolerance equation for other than daylight conditions will require visual con? These scales do not provide a perceptually uniform color space. Consequently, color differences are seldom if ever computed directly from differences in x, y, and Y. The tristimulus values Xn, Yn, Zn de?
Usually, the white object-color stimulus is given by the spectral radiant power of one of the CIE standard illuminants, for example, C, D65 or another phase of daylight, re? Under these conditions, Xn, Yn, Zn are the tristimulus values of the standard illuminant atm Yn equal to This method of computing a metric hue difference loses the information about the sign of the hue difference positive or negative and can be unstable for pairs of colors near the neutral axis.
An alternative method has been proposed 14 that corrects both problems: It is intended to be used as a single-number shade-passing equation. There should not be a need to break the equation down into perceptual components—the CIELAB components of the model do that already. The CMC components and single number tolerances are computed as follows: The most common values are aatm For specimens that are matte, randomly rough, or mildly textured, values intermediate between 1: The color dependent d2424 are de?
It was derived primarily from visual observations of automotive paints on steel panels. Its weighting functions are much simpler than those of the CMC equation. CIE94 tolerances are computed as follows: Those conditions are given in Table 1. The parameters kL, kC, kH, are the parametric factors that can be used to compensate for texture and other specimen presentation effects while kV is used to adjust the size of the tolerance volume for industrial bias.
All the k values default to 1 in the absence of speci? The are computed using the following equations: The equations derived and documented astn standard DIN provides an axes rotation and the logarithmic expansion astk the new axes to match that of the spacing of the CIE94 color tolerance formula aastm the need to make the specimen identi?
Thus computed color differences are based only d2424 the Euclidean distance in the DIN99 space. The v2244 for computing the DIN99 d22244 are: In the process, the researchers came to the conclusion that neither formula was truly optimum. This is contrary to what is observed. Visually, there is no change in the magnitude of the difference between the specimens simply by asgm roles. By using the position of the arithmetic average color between the two specimens to asym the local distortions to CIELAB color space, the roles of the two specimens may be switched without changing the magnitude of the computed colordifference, in full agreement with the visual assessments.
Lightness L99 5 For textiles the following equivalence relations holds: The four color space terms are computed as follows: Precision and Bias The next section, uses data from a commercial collaborative testing program to illustrate precision for one material.
Because of the many trigonometric functions and power functions involved in computing the color space parameters, all computations should be carried out in IEEE? D22244 a typical recent survey Report No. Table 2 gives the mean color differences and their standard deviations for the groups of instruments considered While not obvious from this listing, all displayed angles are assumed to be given in degrees, including Du and thus must generally be converted into radians for trigonometric analysis on digital computers.
Current color tolerance difference equations which base the distortion of CIELAB space on the position of the standard allows a user to prede?
This is convenient for certain textile sorting applications and for graphical quality control charting. Nor is it possible or reasonable to plot groups of colors in terms of the modi?
Thus the equation is highly optimized for pairwise comparison of a product standard to a production test specimen but not for statistical process control.
See Practice E Record the location where these measurements were made on the specimen. Specular component included for integrating-sphere measurements. Examples of Ka and Kb are tabulated in Table X1. Approved May 1, ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such d22244 rights, and the risk of infringement of such rights, are entirely their own responsibility.
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