Example of the cleaning procedure on a 0.36 deg² region containing 4 signal peaks, indicated as a, b, c and d. Each circle is centred on the pixel with the maximum amplitude. The corresponding S/N is also reported, as ‘SNR’. Top panel: Amplitude map before cleaning. Smaller bottom panels: Amplitude map after each of the sequential cleaning steps. The algorithm detects and removes each peak in descending S/N order: first peak a (top-left), then peak b (top-right), peak c (bottom-left), and finally peak d (bottom-right), leaving at the end a map without any significant signal.