Color transformation

Abstract

The color transformation is a crucial step in the analysis of photometric data. Once the data have been reduced to outside the Earth’s atmosphere they have to be compared with standard data obtained at other sites with other telescopes, other filters and other detectors. Even when one works in a well-established system, such as the Johnson- Morgan UBV system (see Chapter 16), the instrumental responses of various equipments are seldom identical, i.e., the ratio of the functions s(λ) is not a constant (this ratio is rarely unity because of differences in the collecting areas, in the filter transparency, and in the detector efficiency, but this is of secondary importance, since it translates directly into a scaling factor or a magnitude zero-point).