Histograms of the ratio of the intrinsic half light radius in the 100 μm (160 μm) band to the half light radius in the 70 μm band, for sources with significant measurements in either band. The numbers of sources with a measurement at 70 μm but only a limit at the longer wavelength are listed in the top left, these will typically have size ratios ~1–2. The case of NGC 1097 (insets) visualizes how a warm central starburst superposed on a cold large disk can cause large ratios R_e,160/R_e,70 from fitting single Gaussians. Overplotted to the inset for each band are the ellipses at half maximum of the elongated Gaussian fit (black) and the beam (red, bottom right).