Information on the individual plots:
All the plots use fake sources inserted during the processing. Fakes can be inserted either into the coadds or at the visit level which was done here. The input magnitudes are the magnitudes that were given to the insertion code in the catalogue of fakes and the output magnitudes are those recovered during the processing.
Magnitude vs Magnitude Difference
This shows how the magnitude difference (between input and recovered) changes with input magnitude, unsurprisingly it gets larger for fainter sources. There is a small offset, I do not know if this is important. The long term plan is to track it and see if it changes.
Blendedness vs Magnitude Difference
Similar to above but with log10(blendedness) on the x axis, again mostly unsurprising more blended things are less well recovered. Possibly a hint that really close pairs are more likely to have their magnitudes over estimated.
Distance to Nearest Neighbour vs Magnitude Difference
The distance to the nearest neighbour is calculated by matching back to the catalogue and taking the second nearest match, based on the assumption that the nearest match is the object itself, this matched object could be anything not just the stars used in the plot. This is plotted against magnitude difference again and also shows nothing particularly surprising.