Exposures including both the positive flux cases (“point” markers) and the negative flux cases (“cross” markers) on the difference images for DC21bwbfe/SN2021bnv (Type Ia SN; r band). Since we include the negative flux cases, we skip the SDSS-style shape and centroid flags and quantities, and the top six features in Table 3 remain. This example illustrates what happens when the features from the SDSS algorithm are unavailable. Here, feature Nos. 4 and 5 are less effective than the others. In both positive and negative flux cases, when the source is sufficiently bright (high S/N in absolute value), the PSF flux S/N itself is sufficient for the candidate selection. However, when it is faint in the positive flux cases, using more features can give better candidate selection (see also Figure 15).