Time evolution of the photospheric properties and the opacity calculated using the HFR method presented in this paper for the NS merger model sym-n1-a6 and assuming a uniform composition corresponding to the full ejecta at t = 3.5 d. Temperature (dotted blue line), density (dotted orange line), and velocity (dotted green line) are scaled by the left y axis and normalized by their values at 1 day. The values at 1 day for these quantities are T_ph (t = 1d) = 2750 K, ρ_ph(t = 1d) = 7.4 × 10⁻¹⁶ g cm³, and υ_ph(t = 1d) = 1.2 × 10¹⁰ cm s⁻¹, respectively. The Planck-averaged opacity for the HFR data (red, dashed line) is plotted on the right y axis. The solid red curve shows the opacity calculated using the parametric opacity function defined by Just et al. (2022), for comparison.