Fourier spectrum of the observation 0720540401 (top-left panel) and the spectrum of the matrix resulting from the difference between 0720540401 and 0720540601 after being properly rotated according to their PAs (top-right panel). The top-left panel shows particular features associated with the stray light with weak counterparts in the right panel. These arc-shaped features were reproduced by applying the Fourier transform to a simulated matrix with uniformly distributed tilt parameters (bottom-left panel), producing the plot shown in the bottom-right panel. ω_x and ω_y represent the frequencies along the two axes.