The effect of the type of background fluctuations on photometric accuracy, for two different surface brightness, μ_V = 21 (upper panel) and μ_V = 17 (lower panel). In each panel three cases are considered for the same stars detected: individually, the theoretical value; on a uniform background; and those detected on a fluctuating background. They are labeled, respectively, individual (red); uniform brightness (green); fluctuations (blue).