Let there be light: and there was light.

Color representation of narrowband emitters

Why color calibration?

Color calibration of astronomical targets is an essential step in getting reproducable results. The most often used methodology is the so called „photometric color calibration“. Based on star colors, which are obtained from a database after a platesolving process, the image is corrected in a way, that the colors of known stars have a best fit to reality. This process is based on white point calibration and therefore only makes sense for desaturated colors, i.e. continuum emitters like stars, star clusters or galaxies. This method will strongly fail for narrowband emiiters. Why this is the case, and how colors of narrowband emitters are best approximated on common imaging devices (monitors, printers), is deduced in the following paper: A numerical solution for correct color rendering of narrowbandemitters in applied astrophotography. (download as pdf)
The image below shows a comparison of conventional color rendering (left side) and the physically correct color rendering (right side). If you have ever oibserved M42 in a larger aperture instrument under good skies, you will remeber the grey-blue greenish tint of the outer regions of the Orion nebula, as you can see them in this image.