Temporal and spatial evolution of the WL emissions in the X2.2 flare on September 6, 2017. (a) and (b): HMI continuum intensity map and LOS magnetogram, respectively. The orange contours mark the flare region. The marked points represent the qualified WL pixels identified by our method, and the colour of the points indicates the different peak times of the WL flux at each point. (c): Histogram of the WL pixels with different peak times. The blue light curve is GOES SXR 1−8 Å flux.