Histograms of temperature in the upper photospheric layers of the surface convection simulations at three different Rosseland optical depths and for the three different treatments of scattering in the radiative transfer solution. Left panel: results for the red giant at  [Fe/H]  =  −3; central panel: turnoff star at  [Fe/H]  =  −3; right panel: red giant at  [Fe/H]  =  −2. The histograms are constructed from snapshots taken at the end of the simulation sequences, for the coherent scattering case (grey bars), Planckian source function and no scattering extinction in optically thin layers (blue curves), and Planckian source function with scattering treated as true absorption (red curves).