Distribution of stars (red) and galaxies (blue) in the r-band concentration space for different magnitude ranges (labelled in the panels) in the J-PLUS EDR pointing 00857. The coloured solid lines mark the PDF-weighted histograms estimated with our probabilistic PDF-based classifier. The coloured areas show the histograms estimated with the SDSS classification of J-PLUS sources. The black solid histogram is the total distribution, illustrating the confusion between compact and extended sources at the faintest magnitudes.