Colorimetry for the stain technologist. II. The specification of chromaticity difference.

This paper describes the calculation of chromaticity difference. The text has been written specifically for the stain technologist and is largely self-contained. The concept of a uniform chromaticity scale (UCS) is described. A UCS is a diagram in which equal perceived differences in chromaticity are represented by equal distances anywhere on the diagram. UCSs are developed by transformations of the CIE 1931 chromaticity diagram, and may be linear (projective) or nonlinear. The effectiveness of the various transformations has been assessed using published data on discrimination of chromaticity. The usefulness of chromaticity difference calculations is illustrated by histological examples, including Romanowsky stained blood cells and Papanicolaou stained cells from the uterine cervix. Six UCSs are used in these examples, two projective and four nonlinear.