Logarithm of the contributions to the Rosseland mean opacities (see text) in the (T, N_e) plane, plotted according to the same scale. Its lower limit is set to −2.5, and the smallest scattering contributions are upper limits. κ_tot is the RMO considering all the absorption processes, κ_{tot − P} is the RMO without process P, P being one of the opacity sources (lines b-b, photoionisation b-f, reverse bremsstrahlung f-f, or scattering, scatt).