that the number of detected points would decrease slowly, as darker kernel points would fall below the increasing threshold. On the other hand, for the thresholds smaller than optimal, the number of false-positive (noise) points would increase rapidly, because they were caused by random fluctuations ($p$-modes for instance) and their location in the field-of-view was not confined to flare kernels.

2.  The spread of the location of the points around their gravity centre evaluated by standard deviation of the positions in both directions independently. The idea behind was that when only flare kernels were detected, they would be sort of confined, whereas when also random noise was detected as false positives, they would be located again all over the field-of-view and the spread would increase.

It turned out that the proposed tests returned an unambiguous value of the optimal threshold value. As it can be seen from Fig. \[fig:sigma\_number\] and \[fig:sigma\_spread\], the behaviour of both selected quantities was as we expected and the optimal value for the threshold was thus 1.88.

![Dependence of the total number of points detected as pixels of WLF kernels in all flares on the the value of $\sigma_M$.[]{data-label="fig:sigma_number"}](sucetbodov.pdf){width="50.00000%"}

![Dependence of a characteristic spread of points 