Correcting Measured Colorimetric Data for Differences in Backing Material

The question of which backing to use when making spectral reflectance measurements has many answers depending on the application and perspective of those using the data. The densitometry standards all call for a black backing to minimize the impact of back printing and to minimize variability due to translucency effects and local variations in opacity and backing uniformity. The color management world finds more consistent results, between visual comparisons of proof and print, when using profiles based on white or self backing. There have been no significant proposals of methods to convert colorimetric data measured with one backing to the values that would have been measured with a different backing. In a CGATS meeting in 2003, the late Hans Ott proposed a method using the ratio of the spectral reflectance of the substrate with the two backing materials of interest (the one used for data collection and the one for which data conversion was desired). In that same CGATS meeting, a method based on the use of the tristimulus values of the substrate over each backing was also proposed. This paper summarizes both methods. It also compares the results of each using measurements of the IT8.7/3 basic data set data printed on coated paper, digital print paper, and newsprint.