Example of our aperture photometry approach applied to the stellar stream detected around NGC 3451. Top panel: input image in g-band, with subtracted sky, showing the stream around it. Middle panel: the detection contour of the galaxy and its stream are highlighted (black line) on a pixel grid 8 × 8 courser than the input image to highlight the low surface brightness signal. Bottom panel: the apertures used to measured the surface brightness, magnitude and colours are placed along the stream (red circles). The foreground stars and background sources are masked (white areas).