Detecting points is fairly simple with the help of standard high pass mask.

By setting a threshold value, this mask detects only points and not lines. Hence point has been detected at the location on which the mask is centered only if

$|R| ≥ T$

where R is derived from the standard convolution formula

$R=w_{1} z_{1}+w_{2} z_{2}+⋯+w_{9} z_{9}$

where R is derived from the standard convolution formula T is a non-negative threshold which is defined by the user. We take |R| because we want to detect both the kinds of points i.e. white points on a black background as well as black points on a white background.

Figure 17