Three steps in construction of the ODF. Left: schematic representation of monochromatic opacities in an interval of wavelengths divided into steps of λ_i. The red vertical lines mark one ODF step with λ ∈ [λ₂, λ₃]. Middle: opacities of that step sorted by magnitude. The distribution is mapped onto the unit interval w ∈ [0, 1] and the wavelength dependence is lost within the step. Right: sorted opacities discretised in ODF substeps.