Hello Barry, Wheeler, Barry wrote:
4. The colors of the cultural heritage materials are not very similar to the colors of the ColorChecker. 5. The more numerous colors of the ColorChecker SG are more similar and might provide a better calibration set.
What do you mean by "similar colors"? similar in terms of spectral properties or just in terms of tristimulus values? I set up a database with approx. 60000 spectral measurements (amongst others many drawdowns of hand-grinded oil pains prepared with ancient pigments after historic recipes in the context of a research project) and found that neither the ColorChecker 24 nor the ColorChecker SG can adequately represent the spectral properties and "metameric challenges" of typical cultural heritage objects to be scanned -- at least not with the sensors and light sources I was confronted with. I chross-checked and confirmed my finding by means of relevant sub-sets of the SOCS Database (ISO/TR 16066: Standard object colour spectra database for colour reproduction evaluation) as well as additional spectral data from paint manufacturers. My research took more than two years and resulted in a tailor-made scanner calibration and profiling target exclusively for Cruse Scanners (with 809 patches). Tests with prototypes are successfully finished and we are starting to manufacture the target right now. Klaus Karcher