A visible-reflectance portable spectrophotometer was used to
measure various colors of this painting. A thin transparent
plastic was used to protect the painting and along with a digital
camera enabled us to determine the approximate measurement position.
Our spectral imaging system was used to estimate the painting's
spectral reflectance. We calculated the average reflectance
for the same area measured by the spectrophotometer.
By moving the spectrophotometer around the painting, you can
see the accuracy of spectral imaging compared with direct measurements.
If you want to know all the details, download our technical
Imai, L.A. Taplin, D.C. Day, E.A. Day, and R.S. Berns, Imaging
at the National Gallery of Art, Washington D.C., MCSL Technical
Report, December 2002. (Download
11.7MB PDF, Download
Lo-Res 2.8MB PDF)