Upper panel: empirical pixel correlation matrices estimated from the reference dataset, the input dataset, the emulated dataset, and the Gaussian dataset in the N_input = 10 case. The color scale runs between −0.1 and 0.1 to highlight the structures and allow for a visual comparison. See Section 5 for details. Bottom panels: zoom-in between pixel 760–840 of the corresponding covariance matrix in the upper panel. Note that here the color scale runs between −1 and 1. See Section 5.3 for further details.