The sensitivity of the eye to small colour differences

The paper records the measurement of small colour steps for various lines across the C.I.E. colour chart. The whole area of the chart has been covered by the author in a series of observations on 35 lines in various directions on the chart, and six of the more important lines have also been tested by three other observers. The results are illustrated graphically by a series of short lines of the appropriate length drawn on the colour diagram and they are also tabulated. The very wide variation in size of step in different parts of the C.I.E. chart is demonstrated. The results have been transformed to the rectangular uniform-chromaticity system of Breckenridge and Schaub, and a much closer approximation to equality in the length of step is apparent, although a considerable discrepancy still exists in the red corner of the chart. The application of the results to the specification of colour tolerances and to the adoption of an agreed uniform chromaticity scale is discussed.