Scatter plot with pixel values of Planck TYPE 1 map as abscissa and pixel values of xGNILC map as ordinate. Top: CO J = 1 → 0; middle: J = 2 → 1; bottom: J = 3 → 2. Planck TYPE 1 maps are smoothed to 10′ resolution, and the HEALPix pixel size is increased to N_side = 256 for this figure. In the inset windows in the upper left corner we show the scatter for low-brightness pixels. In the inset windows located in the bottom right corner, we show the scatter plot in log scale. The orange line indicates y = x in all plots.