2D non-LTE vs. 1D non-LTE (upper panels) and 2D non-LTE vs. 1D LTE (lower panels) abundance corrections for the O I 777 nm triplet integrated over all components as functions of effective temperature for the nine-day (left panels) and three-day (right panels) Cepheid model. The photometric phase ϕ_ph is indicated by colour. Solid and dashed black lines depict the temperature dependence for M9 and M3, respectively, when fittingthe numerical data by a parabola.