Density plots of the distribution of log₁₀(Z_⋆/Z_⊙) as a function of log₁₀[Σ_⋆/(M_⊙ pc⁻²)]. Large light-blue points with error bars represent the median, 16^th and 84^th percentile of the values of log₁₀Z_⋆ per each log₁₀Σ_⋆ bin. Left: The entire data set, consisting of 71 120 654 individual pixels. Only areas with ≥1000 pixels are included. Full, dashed, dash-dotted, and dotted lines represent fits from González Delgado et al. (2014), Zibetti et al. (2020), Neumann et al. (2021), and Zibetti & Gallazzi (2022), respectively. Right: The test data set (consisting of 9 035 270 pixels from 150 galaxies), predicted (top) and true (bottom) Z_⋆ as a function of true Σ_⋆. Only areas with ≥10 pixels are included. Black line and the grey area marks the median, 16^th and 84^th percentile of the whole TNG50 data set (the light-blue points with error bars from the plot on the left), while the light-blue points with error bars represent the median, 16^th and 84^th percentile of log₁₀Z_⋆ for each log₁₀Σ_⋆ bin in the test set.