Page:Journal of the Optical Society of America, volume 33, number 7.pdf/14



IV. COLORIMETRIC DATA

Values of X, Y, Z, x, and y for all of the samples and for the four illuminants, as explained above, together with the. Munsell notations, H V/C (hue, value, and chroma), and the Munsell painting number for each sample, are given in Table II. Values for the neutrals are at the end of the table. Values of z are omitted, since z=1-x-y.

Values of the trilinear coordinates, x and y, for ICI Illuminant C, are plotted in Figs. 2 to 8 for Munsell values 2 to 8, respectively. The x and y values for ICI Illuminant C, and therefore for magnesium oxide and for any other spectrally non-selective sample, are given in each diagram at x=0.3101, y=0.3163. Values of x and y for the Munsell samples obtained at the National Bureau of Standards are plotted as circled points. The data obtained by Glenn and Killian (8) at the Massachusetts Institute of Technology in 1935 are plotted as uncircled points for comparison with the present data. When the two points for a sample coincide, the combination is plotted as a circled point with a short line attached; in many cases, to avoid confusion, the two points are joined by a fine line. Lines are drawn connecting all of the NBS points of constant chroma on each diagram, resulting in the spiderweb-like figures shown. Graphs similar to Figs. 2 to 8 could of course be plotted for the other illuminants using the data given in Table II. While this has not been done for the present paper it has seemed of interest to show the effect of the illuminant on the location and shape of the network. This is done in Fig. 9, where the values of x and y for Munsell value 5 are plotted to the same scale for the four illuminants.

V. COMPARISON WITH GLENN-KILLIAN DATA

Differences between the methods used by Glenn and Killian and those used at the National Bureau of Standards are understood to be as follows: 1. The Glenn-Killian spectrophotometric data were obtained with samples backed by “a standard white substance,” the National Bureau of Standards data with samples backed with black paper. 2. The calibration curves (see above) run on each sheet at the National Bureau of Standards were not used by Glenn and Killian. 3. The Glenn-Killian colorimetric computations were made by the selected-ordinate method, the NBS data by the weighted ordinate method. Spectrophotometric differences caused by the backing are illustrated in Fig. 10, in which are