Maps of a fBm with β = 2.4 (top left), of a decaying exponential with a decay length scale of 100 pixels (top mid), and of a mixed model with the same decaying exponential overlaid onto the fBm with β = 2.4. The maps have a resolution of 1000 × 1000 pixels. All fBms used here are shifted to positive values by adding an arbitrary constant and normalized by their mean values. The bottom panels display the corresponding Δ-variance spectra. An additional spectrum corresponding to an fBm with β = 3.4 is shown in the bottom left subpanel (corresponding map not shown). The values of α = 0.4, 1.4, and 3 are not fits to the spectra, but are shown as a reference to guide the eye.