Comparison of three different reconstruction thresholds for a single observation, overlaid on the Mg II slit-jaw image. The light blue pixels are the spectra reconstructed with an error lower than the chosen reconstruction threshold. The pixels in orange are the spectra reconstructed with an error above the threshold. In the left panel a too low threshold was selected, most pixels are kept. The right panel shows how only areas around the bright ribbon like structure are selected and in the centre panel the bright structure and some areas extending around it are kept.