above has the advantage of allowing the detection of most in individual bands despite their low . However, in most cases (87 galaxies), at least one band was not detected, as the measured flux inside the galaxy is smaller than the flux in the sky annulus. In these cases, we are only able to set an upper limit on the source flux. There are missing detections in most of the bands, but the blue bands are the most affected, in particular the narrow bands F378 and F395, for which there are flux detections in only $\sim 60$% of the galaxies. Nevertheless, in the majority of the cases (97 galaxies), we have flux detections in at least 6 bands, which already provides better spectral coverage in the optical than do the SDSS bands, and 80% of the galaxies have detected flux in at least 9 bands.

In Figure \[fig:detection\_images\], we show a sample of detection images of SMUDGes UDGs, produced by stacking all 12 S-PLUS bands, ordered in decreasing central surface brightness in the $g$ band, $\mu_{0,g}$, and highlight the photometric apertures.

Stellar populations from multi-band observations {#sec:sedfitting}
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We quantify the properties of the stellar populations of our sample by 