Row y = 148 of the demodulated Quiet Sun frame corrected with different algorithms after wavelength calibration on the central row y = 600. The orange line shows the dataset without any smile or flat-field correction applied. For the Wöhl representative dataset (green) the smile was detected using the Fe I line at 5250.6 A (at x = 1150 px) only. The spectroflat method (blue) uses all strong lines in the FOV simultaneously. While both methods agree on the 5250 A lines, they already start to notably diverge on the 5247 A lines (350 pixels apart).