(a)
(b)
(c)
(d)
Figure 2: The time-frequency curve of the ECG fragment when the center frequency is 25hz. (a) The TF-plane WT-based of J wave-positive. (b) The TF-plane WT-based of J wave-negative. (c) The TF-plane SST-based of J wave-positive. (d) The TF-plane SST-based of J wave-negative.