Page:Colorimetry104nime.djvu/50

Table 20. Spectral tristimulus values and between-observer variances and covariances

Wave­length nm	${\overline {x}}_{1}0$	${\overline {y}}_{1}0$	${\overline {z}}_{1}0$	$V({\overline {x}})\times 10^{4}$	$V({\overline {y}})\times 10^{4}$	$V({\overline {z}})\times 10^{4}$	$C({\overline {xy}})\times 10^{4}$	$C({\overline {xz}})\times 10^{4}$	$C({\overline {yz}})\times 10^{4}$
400	0.0191097	0.0020044	0.0860109	1.26	0.012	25.58	0.10	0.68	0.47
410	.84736	.008756	.389366	6.61	.11	132.11	.71	29.38	3.21
420	.204492	.021391	.972542	9.36	.26	193.19	.73	42.06	3.50
430	.314679	.038676	1.55348	7.37	.67	154.07	1.06	32.93	5.09
440	.383734	.062077	1.96728	3.85	.45	97.76	.82	18.93	3.55
450	.370702	.089456	1.99480	3.53	.56	81.53	.41	16.14	1.85
460	.302273	.128201	1.75437	10.93	1.00	206.07	.15	45.40	1.36
470	.195618	.185190	1.31756	11.04	2.72	180.40	1.01	42.31	1.32
480	.080507	.253589	.772125	7.16	6.02	60.63	1.08	18.24	.08
490	.016172	.339133	.415254	6.74	10.45	23.38	.63	9.73	.76
500	.003816	.460777	.218502	4.14	12.87	5.93	.006	2.79	2.45
510	.037465	.606741	.112044	3.25	8.29	1.91	.88	1.12	1.00
520	.117749	.761757	.060709	1.82	4.57	.65	1.09	.32	.18
530	.236491	.875211	.030451	1.43	2.53	.27	1.00	.055	.020
540	.376772	.961988	.014676	6.22	5.90	.43	3.01	.13	.28
550	.529826	.991761	.003988	14.31	6.68	1.05	5.28	.53	.70
560	.705224	.997340	.000000	28.28	8.47	1.00	9.60	1.02	.51
570	.878655	.955552		43.72	9.98	.94	14.20	1.48	.11
580	1.01416	.868934		56.88	11.25	.78	18.12	1.84	.38
590	1.11852	.777405		58.85	9.47	.65	19.41	1.94	.81
600	1.12399	.658341		49.31	7.31	.38	16.98	1.48	.72
610	1.12399	.658341		32.43	4.75	.25	11.63	1.02	.52
620	.856297	.398057		15.87	2.40	.12	6.01	.45	.22
630	.647467	.283493		5.75	.92	.059	2.26	.12	.059
640	.431567	1.79828		.75	.13	.003	.30	.001	.0007
650	.268329	.107633		.47	.079	.0005	.19	.001	.0003
660	.152568	.060281		.46	.071	.0004	.18	.002	.0009
670	.0812606	.0318004		.13	.019	.0002	.049	.001	.0004
680	.0408508	.0159051		.043	.006	.00002	.016	.0001	.0001
690	.0199413	.0077488		.009	.001	.000004	.003	.00003	.00002
700	.00957688	.00371774		.004	.0005	.000002	.001	9 × 10−6	5 × 10−6
710	.00455263	.00176847		.001	.0002	4 × 10−7	.0004	1 × 10−6	9 × 10−7
720	.00217496	.00084619		.0002	.00003	4 × 10−8	7 × 10−5	3 × 10−8	5 × 10−8

Fig. 30.Uncertainty ellipses compared with MacAdam perceptibility ellipses.Correlated uncertainty, solid line ellipses; MacAdam perceptibility, dotted line ellipses. (All ellipses are plotted on a times-ten scale.)

b. Source

Most photoelectric colorimeters are designed for one standard source, usually CIE source C. Such colorimeters do not indicate how closely specimen and standard match for other sources, which depend on the degree of metamerism. Several colorimeters now have provision for inserting an auxiliary filter to approximate a source other than the one supplied.

c. Filter-detector combinations

Most photoelectric tristimulus colorimeters use three filter-detector combinations and approximate the short-wave lobe of the $x$-function by a suitable fraction of the $z$-function. Errors encountered in this type of colorimeter have been treated by Van den Akker [152].

There is some degree of failure to duplicate the CIE color-matching functions even in colorimeters with four filters, one for $y$, one for $z$, and two for the two-lobed $x$. This failure restricts utility of these colorimeters to measurement of the color of specimens of spectral characteristics similar to that of the standard.

If the limitations are appreciated, methods using photoelectric tristimulus colorimeters are useful in product-control colorimetry of nonfluores cent specimens. The National Bureau of Standards has developed three sets of color standards, Non selective standards, KB-Chromatic standards, and S-Chromatic standards, for use with these methods. These standards are now available, either in dividually or in sets, from the Gardner Laboratory. Inc., Bethesda, Md. 20014, and Hunter, Associates Laboratory, Inc., Fairfax, Va. 22030.