pix_drum outputs the (x, y) pixel coordinates of the primary peak. That is, the (x, y) pixel coordinates of the peak that is pressed deeper.

Every other peak is considered a secondary peak. Secondary peaks are detected through changes in concavity.

Secondary peaks are calculated in the following way:

1) a first vector d is the line from the corner to the primary peak.

2) a second vector s is the line from the primary peak to the secondary peak.

3) a third vector p is the projection of s onto d.

4) a fourth vector e is the line from s to p.

Each secondary peak outputs an intensity (length of e) in pixels, the distance or scale (length of p / length of d) and its (x, y) position in pixels.

Lateral intensity is calculated in the following way:

1) the total area T of the two rectangles on each side of the primary peak is calculated.

2) the % of black pixels is substracted from T to get the total black area.

3) to the result of that substraction, we substract the estimate of what % of black pixels would there be with no secondary peaks, where intensity should be zero.