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A recent ASTM specification (ASTM E2214-02) was created to standardize the terminology and procedures used to evaluate color measuring instruments. This specification addresses the need for uniformity among the manufacturers of such instruments when quantifying the performance of their products. The scope of E2214 is necessarily large, covering the procedures required to compare instruments for a variety of metrics, all of which are important to their overall performance. In this work, we will focus on one aspect of the instrument evaluation: repeatability performance. We will present repeatability results from a long-term study of twelve commercial spectrophotometers. Comparisons will be made between traditional color difference metrics and the more complex multidimensional methods specified in E2214.

Part I described an experiment in which the repeatability of a number of common, commercially available spectrocolorimeters was compared using ASTM procedures. ASTM E2214-02 Standard Practice for Specifying and Verifying the Performance of Color-Measuring Instruments is intended to standardize the terminology and procedures used to evaluate color measuring instruments. In this article, we develop reproducibility results from a medium-term study of 10 commercial spectrocolorimeters. The comparisons are presented so as to contrast between the traditional color difference based specifications found in the historical literature and in manufacturer's literature and the more complex multidimensional methods specified in E2214. Instrument to instrument contrasts are reported as well as tests of agreement across a set of instruments as a whole. The results confirm common understandings. Hemispherical diffuse instruments exhibit a higher level of inter-instrument agreement than do bidirectional (45:0) instruments. The results also provide support for a surprising conclusion about the statistical significance of the minor differences in both interinstrument agreement and inter-model agreement for a single manufacturer. Some speculations on the impact of these conclusions to the development of future comparisons of spectrocolorimeters are given.

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