Step size in the Munsell color-order system by pair comparisons near 5Y 7.5/1 and bisections near 10R 7/8.

Pair comparisons were used to assess the perceptual uniformity of the Munsell value (V) and chroma (C) scales near 5Y 7.5/1 for both small (0.25-0.75) and larger (1-2) increments in V and C. We conclude that in this region perceptual linearity is retained down to steps of 0.25 V and C. Bisection experiments showed that around 10R 7/8 perceptual linearity in Munsell hue (H), V, and C was retained down to step sizes of 0.25 H, 0.10 V, and 0.25 C.

Comparative performance of color-measuring instruments; second report.

The comparative performance of twelve different late-model color-measuring instruments was studied for precision (short-term repeatability) and conformance of color measurement and color-difference measurement.The instruments tested included four true and two abridged spectrophotometers and six colorimeters, all being integrating-sphere instruments except three 45 degrees /0 degrees colorimeters. All the colorimeters were individually calibrated for close conformance to CIE coordinates. Forty-four samples taken from the group studied in the previous paper were measured three times on each instrument, by three different well-trained operators. Again, a GE spectrophotometer was considered the reference instrument for conformance studies. Overall, the GE spectrophotometer, the Hunterlab D25D colorimeter, and the Kollmorgen KCS-18 and KCS-40 abridged spectrophotometers demonstrated the best performance. Statistical treatment of the data has been improved vastly since the earlier paper, and some recalculated results are included.

Statistical study of color-measurement instrumentation.

In a statistical study of the variability of instrumental color-measurement data, two instruments (a Kollmorgen KCS-40 colorimeter-abridged spectrophotometer and a General Electric Recording Spectrophotometer equipped with a Davidson and Hemmendinger digital tristimulus integrator) provided three modes of measurement. Ten samples were measured 48 times in each mode. Frequency distributions were constructed for several colorimetric quantities, including tristimulus values, chromaticity coordinates, and color differences from the mean. To allow study of the error involved in the measurement of color-difference pairs, three such pairs were included in the ten samples. The beneficial effects of averaging were quantified.

Current american practice in color measurement.

Current Aimerienn practice in color measurement is reviewed from the standpoint of instrumentation practice, measurement concepts, and computational methods. Instrumentation practice is described for spectrophotometers, abridged spectrophotometers, and tristimulus colorimeters. Measurement variables discussed include photometric and wavelength scales, standards and standardization, illuminating and viewing geometry, and instrument sources simulating standard illuminants. Computation-methods practiced for obtaining color coordinates and color differences are discussed. Topics indirectly related to the measurement step, such as the basis of colorimetry, color mixing laws, and computer color matching, are specifically excluded from this paper.

Effect of illuminating and viewing geometry on the color coordinates of samples with various surface textures.

Color measurements with several different illuminating/viewing geometries were carried out for samples with four different surface textures in four different colors: matte papers, glossy papers, ceramic or porcelain enamel tiles, and polished opaque glasses, with ISCC-NBS color designations moderate pink, pale orange-yellow, dark bluish-green, and dark gray. On a single instrument (Cary 14 spectrophotometer), three geometries were used: normal/diffuse (N/D), diffuse/normal (D/N) and normal/45 degrees (N/45). For comparison, measurements were also made on a GE spectrophotometer (GERS) using near-normal/diffuse geometry. All integrating sphere (diffuse) measurements were made with specular component both included and excluded. Specular gloss and goniophotometric reflectance measurements were made. For these samples, the Cary 14 N/D and GERS results are in good agreement, and the results with N/D and D/N geometries are essentially equivalent, but there is strong evidence of the serious problem of incomplete exclusion of the specular component with all of the integrating sphere geometries when operated in the specular-excluded mode, even with samples normally considered to be highly glossy or highly matte.

Precision of Color Measurement with the GE Spectrophotometer. II: Photometric Accuracy.

The supplementary light method of Reule was applied to calibrate a simple phototube photometer to an absolute accuracy of +/-0.006% (95% confidence limits). The photometer was then used to determine the photometric accuracy of a General Electric recording spectrophotometer. The photometric scale of this instrument was shown to be accurate to within 0.1% over its entire range.

Comparative performance of color-measuring instruments.

The comparative performance of fifteen different color-measuring instruments was studied for precision (short-term repeatability) and accuracy of color measurement and of color difference measurement. For estimates of accuracy, a GE spectrophotometer was considered the referee instrument. The instruments tested included two integrating sphere spectrophotometers, six integrating sphere colorimeters (four of which were individually calibrated for close conformance to CIE coordinates), and seven 45 degrees / normal calorimeters (four of which were individually calibrated for close conformance to CIE coordinates). Up to fifty-three samples were measured, most of them several times, on each instrument. Paint panels, plastics, porcelain enamels, and ceramic tiles were among the samples used. Overall, the well-established IDL D-1 Signature Color-Eye colorimeter-abridged spectrophotometer and the Hunter D25 Color and Color Difference Meter demonstrated the best and next best performance, respectively, in all categories. Several other instruments, both well established and new, were outstanding in one or more respects. All production instruments tested gave generally satisfactory results.