Rescaled (multiplied by PS(PSF)_r/(PS(PSF)⊗PS(Mask))_r) logarithm of the radial power spectrum profiles: the masked instrumental noise term ($PS{(R_{\mathrm{approx}}·\mathrm{Mask}/\sqrt{{\mathrm{Gal}}_{\mathrm{mean}}\otimes \mathrm{PSF}})}_{\mathrm{r}}=PS{(R_{\mathrm{approx}}^{\mathrm{norm}})}_{\mathrm{r}}$) is the cyan line; the observed masked fluctuation (PS(Gal_{mock fluc mask})_r) is the blue line; the right part of Eq. (21) with the real input value of the SBF (${\overline{N}}_{\mathrm{real}}$) is the red line, and with the fitted fluctuation (${\overline{N}}_{\mathrm{fit}}$) is the dashed green line. The selected range of frequencies where the fitting is performed happens between k_fit, i = 75 px⁻¹ and k_fit, f = 400 px⁻¹, marked with a pale yellow vertical region. In this example, the input SBF value is ${\overline{N}}_{\mathrm{real}}={\overline{N}}_{\mathrm{ref}}=22.59$ and the fitted SBF is ${\overline{N}}_{\mathrm{fit}}=22.47$. The embed image is the observed fluctuation Gal_{mock fluc mask} with a circular mask of r₁ ≈ 80 px and r₂ ≈ 332 px applied.