Page:Journal of the Optical Society of America, volume 33, number 7.pdf/55



(1) From Table II it is found that for V=2.4, I.C.I. Y=4.28 percent.

(2) Since V=2.4/, x and y will be found by interpolation between the charts for values 3/ and 2/. On Fig. 3 for 5.0R 3.0/9.9, L.C.1. x =0.548 and y=0.303. On Fig. 2 for 5.0R 2.0/9.9, I.C.1. x =0.553 and y =0.264.

(3) Since 2.4 is 0.4 of the distance from 2.0 toward 3.0, the interpolated chromaticity (x, y) will be that of value 2/ plus 0.4 of the difference resulting when the chromaticity read from Fig. 2 is subtracted from that of Fig. 3. Since x on Fig. 2 is 0.553 and on Fig. 3 is 0.548, the interpolated x will be 0.553+[0.4 (0.548—0.553) ]=0.551.

Similarly, the interpolated y will be

0.264+[0.4 (0.303 —0.264) ]=0.280.

(4) The complete notation for the sample is Y=0.043 (or 4.3 percent); x=0.551, y =0.280.

Still another illustration of the use of the above data is shown in Table III. This table shows the effect of the revision on the notation of the Munsell samples by presenting revised designations for them. The entries for this table were obtained as follows: (a) Given the Munsell sample, the I.C.I. data for them were taken from reports of the National Bureau of Standards (21), Glenn-Killian (9), and Granville-Nickerson-Foss (10); (b) then the value was read from the subcommittee’s Table II and the hue and chroma were interpolated by use of the large originals of Figs. 1-9. There are larger irregularities in the chroma series than in the hue or value series, presumably because of the special difficulties in recognizing chroma and in producing a painted series to represent it.

Color samples are often evaluated by direct reference to charts of the Munsell Book of Color. This evaluation may be sufficient; if not, conversion to the recommended notation may be made directly by use of Table III or, when interpolations are necessary, by use of Figs. 1-9 on which points representing the Book of Color samples have first been spotted (21), (9), (10).

REVISION PROCEDURES

Details of the various procedures employed in arriving at the recommendations above may now be summarized conveniently in relation to each of the Munsell attributes taken separately.

Chroma Adjustments

The chromaticity surface provided by the I.C.I. coordinates themselves is far from perceptual equi-spacing, as several investigators (16), (23), (30) have shown. Even when Nickerson published the first smoothed chroma loci for Munsell colors, the smoothing of averaged visual estimates directly in such a system was recognized as a difficult task. The present smoothing operations demand more guidance for they involve the added complication of extrapolating beyond the published samples.

While an ideal system for psychological smoothing is not available, Adams’ coordinates of chromatic-value afford some of the needed guidance. Plots of Munsell chroma loci on his charts at values 2/ to 8/, inclusive (2), evince sufficient approximation to circularity to facilitate considerably the actual smoothing operation. Once the smooth loci of chroma are located in the Adams’ coordinates they remain smooth when converted to the (x, y)-coordinates. A given point in chromatic-value is defined by