Spectral reconstruction from the synthetic multifrequency imaging example from Sec. 2.5. The top row shows the ground truth spectral index map α(x) (left panels) and spectral deviations log I_δ(x, ν) as defined in Eq. (6). The central panels represent the spectral fluctuations at ν_low and the right ones at ν_hi. The bottom row presents the corresponding posterior mean reconstructions. These highlight the method’s ability to recover both large-scale spectral slopes and localized deviations across the frequency range.