The evaluation of the noticeability of chromaticity differences between very small areas is needed in studies of color graininess. In the present work, color-discrimination data for eleven well-selected chromaticities were determined by a single observer using a matching method for fields subtending (a) 3′ and (b) 4.4°. The data for the large field agree fairly well with those previously published. The comparable results for the 3′ field have been summarized for convenience in the form of a plane uniform chromaticity diagram in which the standard CIE coordinate network is curvilinear. The diagram represents a simplified approximation to the actual results, which would require a curved surface for accurate representation. Nevertheless, the present diagram is suitable for evaluating the large chromaticity differences that are encountered in color graininess and in most other applications of small-field color-discrimination data.
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