Histograms of Ca II K line profile features per brightness bin. Blue: low brightness; green: intermediate brightness; red: high brightness. Upper left: intensity of the K_1v feature. Upper right: intensity of the K_2v features. Lower left: λ_K1r − λ_K1v, the wavelength separation between the K₁ minima. The three-peaked structure of the green and red distributions are caused by the sparse wavelength sampling furthest away from the line core. Lower right: the full-width at half maximum of the emission peak between the K₁ minima. The histograms are normalised so that the sum of all bins times the bin width adds up to one.