Gray-scale plots showing examples of the effectiveness of two morphological techniques on the data from Fig. 1. The pink samples have been set by the SumThreshold algorithm and the yellow samples have additionally been detected with the morphological techniques. Panels a)–c) show results of the SIR operator with η = 0.2 in the time direction and/or η = 0.3 in frequency direction. Panels d)–f) show an ordinary dilation with a horizontal kernel of five pixels and/or a vertical kernel of three pixels.