Total area occupied by pixels with maximum amplitude greater than given amplitudes for the scans on the 5 May (solid lines) and 6 May (dashed lines). A pixel has an LP above a given amplitude if its maximum Stokes Q or U value exceeds that amplitude across the 15648.52 Å line (green lines) and likewise for CP and Stokes V (blue lines). Upper: original level 1 data. Middle: data after PCA filtering. Lower: data after PCA filtering, reconstruction by the RVM and with any Stokes vector with maximum amplitude < σ_t (vertical, red, dashed line) set to zero. The vertical dashed lines indicate the 1, 2, 3, 4 and 5σ (left to right) levels averaged across all frames as measured in the original data. The σ level is averaged for all pixels in a given frame and is specific to a given Stokes vector.