Algorithm flow chart for the Source Extraction Code (SEC) which details the selection of the positions and channels of maser candidates based on the signal-to-noise ratio S/N (top panel; for details, see Sect. 3). Illustration of the process used by the SEC (bottom panel). A 50 × 50 pixel box that starts from the bottom left corner (BLC) iterates first through channels to detect sources until it reaches the top right corner (TRC).