Distribution of H-values for D_w = 40 pixels (∼1′). The red histogram represents the distribution of the real image. The green histogram represents the distribution of the real background, clearly overlapping with the blue histogram, obtained from the simulated background, as expected. We highlight three different H-values with vertical lines, from left to right: 3σ (green), 3.5σ (cyan), and 4σ (violet), representing the chance probability of a spurious detection, as obtained from the simulations. The tail in the real image is apparent.