ASTM 2244-2022 “Calculation of Color Allowable Limits and Color Differences Using Instrumental Color Coordinates”

Meaning and Purpose
5.1 The original CIE color scale based on the three stimulus values X, Y, Z and chromaticity coordinates x, y is not visually uniform. Each subsequent color scale based on CIE values applies a weighting factor to provide a degree of uniformity so that the color differences across regions of the color space will be more comparable. On the other hand, it is unlikely that the same color differences obtained for the same samples evaluated in different color scale systems. To avoid confusion, comparisons should be made only when color differences or associated tolerances between samples are obtained for the same color scale system. For all colors of the specimen, there is no simple factor that can be used to precisely convert the color difference or color tolerance in one system into units of difference or tolerance in another system.

5.2 Color Difference E00 in Δ is highly recommended to use units (6) E* blood group units in the range of 0.0 to 5.0Δ. This color difference equation is applicable and widely used in industrial and commercial applications, including but not limited to automotive, coatings, cosmetics, inks, packaging, paints, plastics, printing, security and textiles.

5.3 Users of the color tolerance equation have found the addition of the three vector color difference components into a single scalar value in each system to be very useful in determining whether the sample color is within the tolerance specified by the standard. However, in order to control for color in production, it may be necessary to know not only the magnitude of the deviation from the standard, but also the direction of this deviation. Information about the direction of small color differences can be included by listing the components determined by the three instruments for color differences.

5.4 Color tolerance selection based on instrument values should be carefully related to a visual assessment of the acceptability of hue, brightness and saturation differences obtained using practice D1729. The three tolerance equations presented here have been extensively tested against such data for textiles and plastics, and have been shown to be consistent with visual assessments, within the experimental uncertainty of visual judgments. This means that the equation itself misclassifies color differences whose frequencies are no greater than those of very experienced visual color matchers.

5.5 Although color difference and color tolerance equations are commonly applied to a variety of light sources, they have been derived or optimized, or both, for daylight illumination. A good correlation with visual judgment may not be obtained when calculations are performed using other light sources. The use of tolerance equations in conditions other than daylight conditions requires visual confirmation of homochromic levels according to practice D4086.

ASTM 2244-2022 “Calculation of Color Allowable Limits and Color Differences Using Instrumental Color Coordinates”

Scope of
1.1 This practice includes the calculation of color tolerances and small color differences between opaque specimens, such as painted panels, plastic patches or textile samples, based on color coordinates measured by an instrument based on daylight illumination. Practice D4086 should be used to verify instrumental results if it is suspected that specimens may be metamorphic, that is, have different spectral curves despite visually similar colors. The tolerances and differences determined by these procedures are expressed in CIE 1976 CIELAB manual color space (1), 2 CMC tolerance units (2), CIE94 tolerance units (3), DIN99o color difference formula given in DIN 6176 (4), or approximately uniform visual color vision in CIEDE2000 color difference units (5).

1.2 For the Product specifications, the Buyer and the Seller shall agree on the allowable color tolerance between the specimen and the reference and the procedure for calculating the color tolerance. Specific color tolerances may be required for each material and use condition, as other appearance factors (e.g., sample proximity, gloss, and texture) may affect the correlation between the size of the measured color difference and its commercial acceptability.

1.3 This standard is not intended to address all safety issues, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.4 This international Standard has been developed in accordance with the internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the Committee on Technical Barriers to Trade of the World Trade Organization.

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