Estimating edge detection uncertainties through artificial star tests. Left panel (a): input (solid) and output (dashed) AGB+RGB artificial star luminosity functions. The input TRGBs for NGC 1448 and NGC 1316 27.3 mag and 27.5 mag, respectively. Middle panel (b): statistical/random (plus signs), systematic (squares), and combined measurement uncertainties (points and lines) associated with the [−1, 0, +1] Sobel edge-detection kernel as a function of GLOESS smoothing scale for each galaxy. Dotted vertical lines mark the chosen level of smoothing for each galaxy. Right panel (c): the distribution of measured TRGB values at the optimal/chosen level of GLOESS smoothing.