IMaX continuum (panel a) and line-core (panel b) contrasts vs. B_LOS. The red curves are the binned contrasts of quiet-Sun areas extracted from the 2013 ARs scans, and the blue curves are taken from Paper I for quiet-Sun observations in 2009. The yellow curves are the result of non-parametric smoothing applied to the scattered data points of quiet-Sun pixels of 2013. The black dashed line is the quiet-Sun level where contrast is equal to unity.