Algorithm 2:

Require: 1 × 9 VRF signal array, $x\left[1\dots 9\right]$. Set center value in the region as $c$, with the number of adjacent points $n$. Evaluate the threshold value by implementing (3), and consider it the new comparison constant, since further comparisons are performed between the threshold value and the difference between the magnitude and value of $c$. Compute the absolute difference, the gradient $g$, between $x\left[i\right]$ and $c$, where $g=\left|x\left[i\right]-c\right|$. Compare the gradient and the threshold value, $g \ge threshold$ and, if the result is true, represent by 1, if not indicate as 0. The resultant binary code is converted into a decimal code.