in a given observational block, there are only small seeing variations among all bands for each tile (mean standard deviation among bands of 0.14). We conclude that there is no need to homogenize the seeing across the images for our photometry.

For each UDG, we perform aperture photometry in each of the 12 bands from S-PLUS using the <span style="font-variant:small-caps;">photutils</span> package [@Bradley_2019_2533376]. To ensure consistent photometry, for each UDG we define an elliptical aperture with a semi-major axis length of $R_e$, and location, position angle and ellipticity determined from the <span style="font-variant:small-caps;">GALFIT</span> Sérsic profile fitting from the SMUDGes analysis. We subtract local sky using an elliptical annulus with inner and outer radii of $2.5R_e$ and $4R_e$, respectively. Presuming that the Sérsic profile is a good approximation to the surface brightness profile of the UDGs, this annulus is large enough to avoid contamination of the sky region by the galaxy itself [see @2005PASA...22..118G]. We use sigma-clipping to remove the contribution of other sources when we estimate the median background. All observed magnitudes are corrected for the foreground Galactic extinction using the dust maps from @1998ApJ...500..525S recalibrated by @2011ApJ...737..103S assuming that $R_V=3.1$ for the Milky Way .

The aperture photometry method described 