Prominence

The prominence of a peak measures how much the peak stands out due to its intrinsic height and its location relative to other peaks. A low isolated peak can be more prominent than one that is higher but is an otherwise unremarkable member of a tall range.

To measure the prominence of a peak:

1. Place a marker on the peak.

2. Extend a horizontal line from the peak to the left and right until the line does one of the following:

   • Crosses the signal because there is a higher peak

   • Reaches the left or right end of the signal

3. Find the minimum of the signal in each of the two intervals defined in Step 2. This point is either a valley or one of the signal endpoints.

4. The higher of the two interval minima specifies the reference level. The height of the peak above this level is its prominence.

findpeaks makes no assumption about the behavior of the signal beyond its endpoints, whatever their height. As a result, Steps 2 and 4 disregard signal behavior beyond endpoints, which often affects the value of the reference level. Consider for example the peaks of this signal:

Peak Number	Left Interval Lies Between Peak and	Right Interval Lies Between Peak and	Lowest Point on the Left Interval	Lowest Point on the Right Interval	Reference Level (Highest Minimum)
1	Left end	Crossing due to peak 2	Left endpoint	a	a
2	Left end	Right end	Left endpoint	h	Left endpoint
3	Crossing due to peak 2	Crossing due to peak 4	b	c	c
4	Crossing due to peak 2	Crossing due to peak 6	b	d	b
5	Crossing due to peak 4	Crossing due to peak 6	d	e	e
6	Crossing due to peak 2	Right end	d	h	d
7	Crossing due to peak 6	Crossing due to peak 8	f	g	g
8	Crossing due to peak 6	Right end	f	h	f
9	Crossing due to peak 8	Crossing due to right endpoint	h	i	i