A time–frequency image of FAST data for 0.05 s in the frequency range from 1000 to 1500 MHz with an SED curve on the right, a frequency-integral curve in the lower panel, and a zoomed view of the RFI region as the main panel. A narrow-band RFI and a broad-band RFI can be identified from the peaks on the SED curve. The blob RFI contaminates only a small ratio of pixels and cannot be identified based on the SED curve. The colour bar of the image is shown at the top of the time–frequency image.