Estimate of HD 189733b’s global brightness distribution in the IRAC 8-μm channel using the Γ₂ brightness model. Left: relative brightness distribution at HD 189733b’s dayside. Right: dayside standard deviation. Because of its increased complexity, the Γ₂ brightness model enable more localized structure that are less constrained in amplitude (by the occultation depth) and in longitudinal localization (by the phase curve) than large-and-fixed-structure model, e.g., the Γ_SH,1 model (see Fig. 7). However, it is well-constrained in latitude by the secondary-eclipse scanning that is sensitive to confined brightness structure. These model-induced constraints are observable on the dayside standard deviation that shows a maximum at the brightness peak localization and extended wings towards west and east along the planetary equator, because the BDs accepted along the MCMC simulations mainly affect the former by their amplitude change and the latter by their structure change (see Fig. A.1b).