## 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 NumberLeft Interval Lies Between Peak andRight Interval Lies Between Peak andLowest Point on the Left IntervalLowest Point on the Right IntervalReference Level (Highest Minimum)
1Left endCrossing due to peak 2Left endpointaa
2Left endRight endLeft endpointhLeft endpoint
3Crossing due to peak 2Crossing due to peak 4bcc
4Crossing due to peak 2Crossing due to peak 6bdb
5Crossing due to peak 4Crossing due to peak 6dee
6Crossing due to peak 2Right enddhd
7Crossing due to peak 6Crossing due to peak 8fgg
8Crossing due to peak 6Right endfhf
9Crossing due to peak 8Crossing due to right endpointhii