Ca II K contrast plotted against the unsigned LOS magnetic flux density divided by μ (|B_LOS|/μ) for all pixel pairs (excluding sunspots) in all available images. The pixels are colour-coded denoting the logarithm of the number density within bins of 1 G and 0.01 in contrast. The contour lines give the logarithm of the pixel number density in intervals of 0.5. Curves show 5000-point running means (over |B_LOS|/μ in yellow, over contrast in light blue, and their bisector in purple), as well as PF (red), PFL (blue), and LFL (green) fits on the binned curve over |B_LOS|/μ (yellow curve). The vertical grey dashed line denotes the 20 G threshold in |B_LOS|/μ. A magnified section for low |B_LOS|/μ is shown at the lower right corner of the figure to illustrate the differences of the different fits over that region. Also shown are histograms of |B_LOS|/μ within 3 ranges of contrast values (right) and histograms of Ca II K contrast for 4 ranges of |B_LOS|/μ (top). The ranges used for the histograms are shown on the upper part of the corresponding sub-plot.