Low-resolution (30′′ × 30′′) LOFAR image of the cluster A478 at 144 MHz. The contour levels are (1, 2, 4)  ×  3σ, where σ = 620 μJy beam⁻¹. No mock mini halo is injected in the data set in the top left panel. A mock mini halo with I₀ = 1 μJy arcsec⁻² is injected at the cluster centre with r_e = 100 kpc in the top right panel. A mock mini halo with I₀ = 13 μJy arcsec⁻² is injected at the cluster centre with r_e = 25 kpc at the cluster centre in the bottom right panel, and in a close-by void region in the bottom left panel. The values for r_e and I₀ are chosen accordingly to the top panel of Fig. 7 in Murgia et al. (2009) and are referred to measurements at 1.4 GHz.