Comparison between the PPI4 P maps in absence (only CIB, left side) and in presence (right side) of a strong foreground (1000 MJy/sr; see Sect. 5.5) illustrating the different behavior of the CIB confusion noise depending on the foreground strength. Since P is much higher on the right side, we subtracted the mean of each side to obtain a better visualization. The yellow circle in the top left corner shows the instrumental beam size.