Galaxy counts in the g′ (left) and r′ (right) bands for magnitudes r′ > 22 where the background must be subtracted statistically, in logarithmic scale. The counts in Abell 1758 North and South are drawn in red and green respectively. The magenta dashed lines show the galaxy counts from the “local” background extracted in the annulus shown in Fig. 2. Error bars are Poissonian and are not plotted for clarity.