IMcProfileEdgesThresholdForEdge Property

Property Value

Type: Double

The ThresholdForEdge is a given value from zero to 100, where lower values will find more edges than higher values. To mark an edge, the weighted profile (available from the WeightedProfiles property) must transition to above threshold and then transition again to below threshold (with some hysteresis). When the mcpeofAbsoluteThresholding bit of OptionFlags is off (this is the default state), then ThresholdForEdge is a percentage of the difference between the mean and peak weighted values along a profile. However, the actual weighted profile threshold is not allowed to be smaller than a minimum percentage of the AbsoluteMaxWeightValue. This minimum percentage is made smaller as a non-linear function of ThresholdForEdge. The effect is that very bad profiles will yield no edges, but by setting ThresholdForEdge lower you will accept very much poorer edges as the minimum acceptable. To avoid this "minimum edge quality" effect, you could set MinEdgesPerProfile to 1 (or whatever number you are expecting), in which case all but virtually flat weighted profiles will yield the minimum number of "egdes". However, when looking for an unknown number of "edges" based on subtle or small patterns in weighted profiles, it is often best to turn the mcpeofAbsoluteThresholding bit of OptionFlags on, so that ThresholdForEdge represents a fixed percentage of the theoretically maximum weighted value, given by the AbsoluteMaxWeightValue property. When this flag is set, appropriate values for the McProfilesEdges.ThresholdForEdge property can be very low (that is interesting "edges" often result in a weighted profile peak that is a small percentage of the best possible peak). ThresholdForEdge values of 5 to 10 are typical when the mcpeofAbsoluteThresholding bit is set, while ThresholdForEdge values of 25 to 75 are typical when the bit is clear. After a FindEdges call, the actual weighted profile value used for the threshold of each profile is available in the McProfileEdgesEx.WeightedThresholds property.