Stages of the CAAPR aperture-fitting process, using SPIRE 250 μm data for DustPedia galaxy NGC 5364 as an example. Panel 1: central 1000″ × 1000″ portion of map. Panel 2: all of the pixels with S/N> 3. Panel 3: contiguous set of significant pixels isolated as being associated with target source. Panel 4: isolated pixels after being subjected to binary opening. Panel 5: vertices of convex hull of isolated pixels (red dots). Panel 6: best-fit ellipse to convex hull of isolated pixels (solid line). Panel 7: smoothed copy of map, with coarse radial profiling (dashed lines) to find interval within which S/N = 2 (solid lines). Panel 8: region that undergoes detailed radial profiling (dotted shading) to find exact semi-major axis at which S/N = 2 (solid line). Panel 9: resulting elliptical aperture, before (dashed line) and after (solid line) being multiplied by 1.25 expansion factor. Panel 10: final photometric aperture (solid line), found by combining aperture fitted in this band (dotted line) with those fitted in all other bands; final background annulus is also shown (dashed lines).