Covariance (upper right triangle) and correlation (lower left triangle) matrices of the MATISSE spectrum of β Pic b. In order to highlight the off-diagonal correlations in the L band, the covariance values are clipped between 3 × 10⁻³⁵ and 3 × 10⁻³³ W² m⁻⁴ μm⁻² and the correlation values between 0.01 and 1. Two lines of off-diagonal correlations are further highlighted with arrows for readability.