Influence of the various degradation steps on the histogram of the BP circular polarization degree. The degradation was applied to the 30 G MHD simulations. The black line corresponds to the data that were only spectrally degraded. An additional spatial degradation results in the blue histogram. The green line also includes the effect of stray light contamination, while the fully degraded BP signals, i.e., including noise, give the histogram colored in red.