Determination of the TRGB. i′-band luminosity function (a) and smoothed luminosity function (b) are shown in the top panels before and after completeness correction (dashed and solid lines, respectively). Outputs of the edge-detection filter are shown in the bottom two panels, calculated using the photometric error as determined from artificial star tests (c), and calculated using a photometric error four times larger than calculated from artificial star tests (d); line types are the same as in the top panels.