This calculation requires determining two key parameters: the temperature of the ejecta's photosphere and its expansion velocity.
The temperature is typically found by fitting a blackbody curve to the continuum spectrum.
[3] Because the method relies on intrinsic luminosity of supernova, it is independent from the cosmic distance ladder, and doesn't require external calibration.
These account for electron scattering in the supernova's atmosphere causing it to deviate from a perfect blackbody.
Different sets of dilution factors have been published, notably by Eastman et al. (1996) and Dessart & Hillier (2005).