Estimate of HD 189733b’s global brightness distribution in the IRAC 8-μm channel using the Γ_SH,1 brightness model. Left: relative brightness distribution at HD 189733b’s dayside. Right: dayside standard deviation. Because of its fixed and large structure, the Γ_SH,1 brightness model is well-constrained in amplitude (by the occultation depth) and in longitudinal localization (by the phase curve). However, it is less constrained in latitude (by the secondary-eclipse scanning) than more confined model (schematic description in Fig. 3), e.g., Γ₂ (see Fig. 8). These model-induced constraints are observable on the dayside standard deviation; which is significantly lower than for more complex brightness models (see Figs. 8, 11a and b) and is related to its gradient, because the BDs accepted along the MCMC simulations differ from each other mainly in latitudinal orientation (see Fig. A.1a).