Specifications

Submitted to Studies in Conservation, March 2006
12
sources (nominal CCT of 5000 K) and the image rendered on a color-managed CRT display [3].
Their digital master image files included these visual adjustments.
The colorimetric accuracy of Pot of Geraniums is summarized in Table 5. The Quantix-
LCTF system had the best colorimetric performance on average, likely a result of using diffuse
rather than directional illumination. This underscores how lighting for aesthetic purposes may
not result in optimal images for scientific purposes. The MCSL-Sinar system had slightly lower
average accuracy than the Quantix-LCTF system. Given the aesthetic-oriented lighting, this was
an excellent result. The color-managed NGA-Sinar system image before visual editing also had
good performance given its intrinsic limitations as a three-channel RGB device. Statistically,
these three systems were not significantly different from one another. The uncertainty in
comparing in-situ measurements with spectral imaging increased variability [2] compared with
color targets; consequently, the performance differences were not statistically significant.
A disappointing, although common [21, 22], result was that the visual editing decreased
accuracy dramatically. Average ∆E
00
increased by over 50%. This digital master was statistically
significantly worse than the other three images at an α of 0.01. Some of the possible reasons for
the increased error might have been a poorly color-managed display, unmatched white points in
terms of chromaticity and luminance resulting in light and chromatic adaptation differences
between the viewing illuminant and display, differences in lighting geometry between the
imaging system (directional Xenon strobe) and the viewing environment (overhead fluorescent
daylight), differences in image size, and observer metamerism. The color changes were
reductions in chroma and lightness.
The spectral performance is shown in Table 6 and Figures 7 and 8. The MCSL-Sinar
system had reasonable performance, well capturing the spectral characteristics of the painting
throughout the majority of the sampled spectrum. Similar to the ColorChecker results, both
systems had poor performance at short wavelengths, as seen in Figure 8. The average RMS
difference as a function of wavelength was centered about zero for the MCSL-Sinar systen
whereas for the Quantix-LCTF system, there was a systematic under-prediction in spectral
reflectance factor. This was a result of geometric differences between the camera taking