Top left panel: synthetic stellar disk image in the FLUOR filter for the simulation with [Fe/H ]  = −3.0 and log g = 1.6 tiled using only one intensity map at different μ-angles (see text for details). The granulation pattern is continuous. The intensity range is [5000, 0.11 × 10⁶] erg cm^-2 s^-1 Å^-1. Top right panel: synthetic stellar disk image in the same filter and using the same intensity map but flipping the y-axis every second tile to remove the periodicity at the side of each box. Bottom panel: ratio of the fluctuations of the synthetic visibility curves derived from the above images: σ_ref/vis_ref refers to top left panel and σ_shuffle/vis_shuffle to top right panel.