There are 2 types of noises, continuous noise, and coincidence noise. The continuous noise is a pixel fired mostly in an event. It can be removed easily by maksing the pixel. But coincidence noise occurs randomly on any pixel in ALPIDE. If masking all pixels when they are fired at pedestal, it makes contamination of data. Some of this can be removed by increasing threshold. Although changing threshold, the few coincidence noise can be survived. So masking and unmasking cases are drawn simulatneously.
Criteria of hot pixel
Pixels that fired one more time onto pedestal hitmaps
Hitmap of A4W975R7 chip